| Message ID | 164021479106.640689.17404516570194656552.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| Headers | show |
| Series | fscache, cachefiles: Rewrite | expand |
On Wed, 2021-12-22 at 23:13 +0000, David Howells wrote: > Here's a set of patches implements a rewrite of the fscache driver and a > matching rewrite of the cachefiles driver, significantly simplifying the > code compared to what's upstream, removing the complex operation scheduling > and object state machine in favour of something much smaller and simpler. > > The patchset is structured such that the first few patches disable fscache > use by the network filesystems using it, remove the cachefiles driver > entirely and as much of the fscache driver as can be got away with without > causing build failures in the network filesystems. The patches after that > recreate fscache and then cachefiles, attempting to add the pieces in a > logical order. Finally, the filesystems are reenabled and then the very > last patch changes the documentation. > > > WHY REWRITE? > ============ > > Fscache's operation scheduling API was intended to handle sequencing of > cache operations, which were all required (where possible) to run > asynchronously in parallel with the operations being done by the network > filesystem, whilst allowing the cache to be brought online and offline and > to interrupt service for invalidation. > > With the advent of the tmpfile capacity in the VFS, however, an opportunity > arises to do invalidation much more simply, without having to wait for I/O > that's actually in progress: Cachefiles can simply create a tmpfile, cut > over the file pointer for the backing object attached to a cookie and > abandon the in-progress I/O, dismissing it upon completion. > > Future work here would involve using Omar Sandoval's vfs_link() with > AT_LINK_REPLACE[1] to allow an extant file to be displaced by a new hard > link from a tmpfile as currently I have to unlink the old file first. > > These patches can also simplify the object state handling as I/O operations > to the cache don't all have to be brought to a stop in order to invalidate > a file. To that end, and with an eye on to writing a new backing cache > model in the future, I've taken the opportunity to simplify the indexing > structure. > > I've separated the index cookie concept from the file cookie concept by C > type now. The former is now called a "volume cookie" (struct > fscache_volume) and there is a container of file cookies. There are then > just the two levels. All the index cookie levels are collapsed into a > single volume cookie, and this has a single printable string as a key. For > instance, an AFS volume would have a key of something like > "afs,example.com,1000555", combining the filesystem name, cell name and > volume ID. This is freeform, but must not have '/' chars in it. > > I've also eliminated all pointers back from fscache into the network > filesystem. This required the duplication of a little bit of data in the > cookie (cookie key, coherency data and file size), but it's not actually > that much. This gets rid of problems with making sure we keep netfs data > structures around so that the cache can access them. > > These patches mean that most of the code that was in the drivers before is > simply gone and those drivers are now almost entirely new code. That being > the case, there doesn't seem any particular reason to try and maintain > bisectability across it. Further, there has to be a point in the middle > where things are cut over as there's a single point everything has to go > through (ie. /dev/cachefiles) and it can't be in use by two drivers at > once. > > > ISSUES YET OUTSTANDING > ====================== > > There are some issues still outstanding, unaddressed by this patchset, that > will need fixing in future patchsets, but that don't stop this series from > being usable: > > (1) The cachefiles driver needs to stop using the backing filesystem's > metadata to store information about what parts of the cache are > populated. This is not reliable with modern extent-based filesystems. > > Fixing this is deferred to a separate patchset as it involves > negotiation with the network filesystem and the VM as to how much data > to download to fulfil a read - which brings me on to (2)... > > (2) NFS and CIFS do not take account of how the cache would like I/O to be > structured to meet its granularity requirements. Previously, the > cache used page granularity, which was fine as the network filesystems > also dealt in page granularity, and the backing filesystem (ext4, xfs > or whatever) did whatever it did out of sight. However, we now have > folios to deal with and the cache will now have to store its own > metadata to track its contents. > > The change I'm looking at making for cachefiles is to store content > bitmaps in one or more xattrs and making a bit in the map correspond > to something like a 256KiB block. However, the size of an xattr and > the fact that they have to be read/updated in one go means that I'm > looking at covering 1GiB of data per 512-byte map and storing each map > in an xattr. Cachefiles has the potential to grow into a fully > fledged filesystem of its very own if I'm not careful. > > However, I'm also looking at changing things even more radically and > going to a different model of how the cache is arranged and managed - > one that's more akin to the way, say, openafs does things - which > brings me on to (3)... > > (3) The way cachefilesd does culling is very inefficient for large caches > and it would be better to move it into the kernel if I can as > cachefilesd has to keep asking the kernel if it can cull a file. > Changing the way the backend works would allow this to be addressed. > > > BITS THAT MAY BE CONTROVERSIAL > ============================== > > There are some bits I've added that may be controversial: > > (1) I've provided a flag, S_KERNEL_FILE, that cachefiles uses to check if > a files is already being used by some other kernel service (e.g. a > duplicate cachefiles cache in the same directory) and reject it if it > is. This isn't entirely necessary, but it helps prevent accidental > data corruption. > > I don't want to use S_SWAPFILE as that has other effects, but quite > possibly swapon() should set S_KERNEL_FILE too. > > Note that it doesn't prevent userspace from interfering, though > perhaps it should. (I have made it prevent a marked directory from > being rmdir-able). > > (2) Cachefiles wants to keep the backing file for a cookie open whilst we > might need to write to it from network filesystem writeback. The > problem is that the network filesystem unuses its cookie when its file > is closed, and so we have nothing pinning the cachefiles file open and > it will get closed automatically after a short time to avoid > EMFILE/ENFILE problems. > > Reopening the cache file, however, is a problem if this is being done > due to writeback triggered by exit(). Some filesystems will oops if > we try to open a file in that context because they want to access > current->fs or suchlike. > > To get around this, I added the following: > > (A) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network > filesystem inode to indicate that we have a usage count on the > cookie caching that inode. > > (B) A flag in struct writeback_control, unpinned_fscache_wb, that is > set when __writeback_single_inode() clears the last dirty page > from i_pages - at which point it clears I_PINNING_FSCACHE_WB and > sets this flag. > > This has to be done here so that clearing I_PINNING_FSCACHE_WB can > be done atomically with the check of PAGECACHE_TAG_DIRTY that > clears I_DIRTY_PAGES. > > (C) A function, fscache_set_page_dirty(), which if it is not set, sets > I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to pin the > cache resources. > > (D) A function, fscache_unpin_writeback(), to be called by > ->write_inode() to unuse the cookie. > > (E) A function, fscache_clear_inode_writeback(), to be called when the > inode is evicted, before clear_inode() is called. This cleans up > any lingering I_PINNING_FSCACHE_WB. > > The network filesystem can then use these tools to make sure that > fscache_write_to_cache() can write locally modified data to the cache > as well as to the server. > > For the future, I'm working on write helpers for netfs lib that should > allow this facility to be removed by keeping track of the dirty > regions separately - but that's incomplete at the moment and is also > going to be affected by folios, one way or another, since it deals > with pages. > > > These patches can be found also on: > > https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-rewrite > > David > > > Changes > ======= > ver #4: > - Dropped a pair of patches to try and cope with multipage folios in > afs_write_begin/end() - it should really be done in the caller[7]. > - Fixed the use of sizeof with memset in cifs. > - Removed an extraneous kdoc param. > - Added a patch to add a tracepoint for fscache_use/unuse_cookie(). > - In cifs, tcon->vol_create_time is __le64 so doesn't need cpu_to_le64(). > - Add an expanded version of a patch to use current_is_kswapd() instead of > !gfpflags_allow_blocking()[8]. > - Removed a couple of debugging print statements. > > ver #3: > - Fixed a race in the cookie state machine between LRU discard and > relinquishment[4]. > - Fixed up the hashing to make it portable[5]. > - Fixed up some netfs coherency data to make it portable. > - Fixed some missing NFS_FSCACHE=n fallback functions in nfs[6]. > - Added a patch to store volume coherency data in an xattr. > - Added a check that the cookie is unhashed before being freed. > - Fixed fscache to use remove_proc_subtree() to remove /proc/fs/fscache/. > > ver #2: > - Fix an unused-var warning due to CONFIG_9P_FSCACHE=n. > - Use gfpflags_allow_blocking() rather than using flag directly. > - Fixed some error logging in a couple of cachefiles functions. > - Fixed an error check in the fscache volume allocation. > - Need to unmark an inode we've moved to the graveyard before unlocking. > - Upgraded to -rc4 to allow for upstream changes to cifs. > - Should only change to inval state if can get access to cache. > - Don't hold n_accesses elevated whilst cache is bound to a cookie, but > rather add a flag that prevents the state machine from being queued when > n_accesses reaches 0. > - Remove the unused cookie pointer field from the fscache_acquire > tracepoint. > - Added missing transition to LRU_DISCARDING state. > - Added two ceph patches from Jeff Layton[2]. > - Remove NFS_INO_FSCACHE as it's no longer used. > - In NFS, need to unuse a cookie on file-release, not inode-clear. > - Filled in the NFS cache I/O routines, borrowing from the previously posted > fallback I/O code[3]. > > > Link: https://lore.kernel.org/r/cover.1580251857.git.osandov@fb.com/ [1] > Link: https://lore.kernel.org/r/20211207134451.66296-1-jlayton@kernel.org/ [2] > Link: https://lore.kernel.org/r/163189108292.2509237.12615909591150927232.stgit@warthog.procyon.org.uk/ [3] > Link: https://lore.kernel.org/r/599331.1639410068@warthog.procyon.org.uk/ [4] > Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com [5] > Link: https://lore.kernel.org/r/61b90f3d.H1IkoeQfEsGNhvq9%lkp@intel.com/ [6] > Link: https://lore.kernel.org/r/CAHk-=wh2dr=NgVSVj0sw-gSuzhxhLRV5FymfPS146zGgF4kBjA@mail.gmail.com/ [7] > Link: https://lore.kernel.org/r/1638952658-20285-1-git-send-email-huangzhaoyang@gmail.com/ [8] > > > References > ========== > > These patches have been published for review before, firstly as part of a > larger set: > > Link: https://lore.kernel.org/r/158861203563.340223.7585359869938129395.stgit@warthog.procyon.org.uk/ > > Link: https://lore.kernel.org/r/159465766378.1376105.11619976251039287525.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/159465784033.1376674.18106463693989811037.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/159465821598.1377938.2046362270225008168.stgit@warthog.procyon.org.uk/ > > Link: https://lore.kernel.org/r/160588455242.3465195.3214733858273019178.stgit@warthog.procyon.org.uk/ > > Then as a cut-down set: > > Link: https://lore.kernel.org/r/161118128472.1232039.11746799833066425131.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/161161025063.2537118.2009249444682241405.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/161340385320.1303470.2392622971006879777.stgit@warthog.procyon.org.uk/ # v3 > Link: https://lore.kernel.org/r/161539526152.286939.8589700175877370401.stgit@warthog.procyon.org.uk/ # v4 > Link: https://lore.kernel.org/r/161653784755.2770958.11820491619308713741.stgit@warthog.procyon.org.uk/ # v5 > > I split out a set to just restructure the I/O, which got merged back in to > this one: > > Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/163189104510.2509237.10805032055807259087.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ # v3 > Link: https://lore.kernel.org/r/163551653404.1877519.12363794970541005441.stgit@warthog.procyon.org.uk/ # v4 > > ... and a larger set to do the conversion, also merged back into this one: > > Link: https://lore.kernel.org/r/163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/163492911924.1038219.13107463173777870713.stgit@warthog.procyon.org.uk/ # v2 > > Older versions of this one: > > Link: https://lore.kernel.org/r/163819575444.215744.318477214576928110.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/163906878733.143852.5604115678965006622.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/163967073889.1823006.12237147297060239168.stgit@warthog.procyon.org.uk/ # v3 > > Proposals/information about the design have been published here: > > Link: https://lore.kernel.org/r/24942.1573667720@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/2758811.1610621106@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/1441311.1598547738@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/160655.1611012999@warthog.procyon.org.uk/ > > And requests for information: > > Link: https://lore.kernel.org/r/3326.1579019665@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/4467.1579020509@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/3577430.1579705075@warthog.procyon.org.uk/ > > I've posted partial patches to try and help 9p and cifs along: > > Link: https://lore.kernel.org/r/1514086.1605697347@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/1794123.1605713481@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/241017.1612263863@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/270998.1612265397@warthog.procyon.org.uk/ > > --- > Dave Wysochanski (1): > nfs: Convert to new fscache volume/cookie API > > David Howells (65): > fscache, cachefiles: Disable configuration > cachefiles: Delete the cachefiles driver pending rewrite > fscache: Remove the contents of the fscache driver, pending rewrite > netfs: Display the netfs inode number in the netfs_read tracepoint > netfs: Pass a flag to ->prepare_write() to say if there's no alloc'd space > fscache: Introduce new driver > fscache: Implement a hash function > fscache: Implement cache registration > fscache: Implement volume registration > fscache: Implement cookie registration > fscache: Implement cache-level access helpers > fscache: Implement volume-level access helpers > fscache: Implement cookie-level access helpers > fscache: Implement functions add/remove a cache > fscache: Provide and use cache methods to lookup/create/free a volume > fscache: Add a function for a cache backend to note an I/O error > fscache: Implement simple cookie state machine > fscache: Implement cookie user counting and resource pinning > fscache: Implement cookie invalidation > fscache: Provide a means to begin an operation > fscache: Count data storage objects in a cache > fscache: Provide read/write stat counters for the cache > fscache: Provide a function to let the netfs update its coherency data > netfs: Pass more information on how to deal with a hole in the cache > fscache: Implement raw I/O interface > fscache: Implement higher-level write I/O interface > vfs, fscache: Implement pinning of cache usage for writeback > fscache: Provide a function to note the release of a page > fscache: Provide a function to resize a cookie > cachefiles: Introduce rewritten driver > cachefiles: Define structs > cachefiles: Add some error injection support > cachefiles: Add a couple of tracepoints for logging errors > cachefiles: Add cache error reporting macro > cachefiles: Add security derivation > cachefiles: Register a miscdev and parse commands over it > cachefiles: Provide a function to check how much space there is > vfs, cachefiles: Mark a backing file in use with an inode flag > cachefiles: Implement a function to get/create a directory in the cache > cachefiles: Implement cache registration and withdrawal > cachefiles: Implement volume support > cachefiles: Add tracepoints for calls to the VFS > cachefiles: Implement object lifecycle funcs > cachefiles: Implement key to filename encoding > cachefiles: Implement metadata/coherency data storage in xattrs > cachefiles: Mark a backing file in use with an inode flag > cachefiles: Implement culling daemon commands > cachefiles: Implement backing file wrangling > cachefiles: Implement begin and end I/O operation > cachefiles: Implement cookie resize for truncate > cachefiles: Implement the I/O routines > fscache, cachefiles: Store the volume coherency data > cachefiles: Allow cachefiles to actually function > fscache, cachefiles: Display stats of no-space events > fscache, cachefiles: Display stat of culling events > afs: Convert afs to use the new fscache API > afs: Copy local writes to the cache when writing to the server > afs: Skip truncation on the server of data we haven't written yet > 9p: Use fscache indexing rewrite and reenable caching > 9p: Copy local writes to the cache when writing to the server > nfs: Implement cache I/O by accessing the cache directly > cifs: Support fscache indexing rewrite (untested) > fscache: Rewrite documentation > fscache: Add a tracepoint for cookie use/unuse > 9p, afs, ceph, cifs, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking() > > Jeff Layton (2): > ceph: conversion to new fscache API > ceph: add fscache writeback support > > > .../filesystems/caching/backend-api.rst | 850 ++++------ > .../filesystems/caching/cachefiles.rst | 6 +- > Documentation/filesystems/caching/fscache.rst | 525 ++---- > Documentation/filesystems/caching/index.rst | 4 +- > .../filesystems/caching/netfs-api.rst | 1136 ++++--------- > Documentation/filesystems/caching/object.rst | 313 ---- > .../filesystems/caching/operations.rst | 210 --- > Documentation/filesystems/netfs_library.rst | 16 +- > fs/9p/Kconfig | 2 +- > fs/9p/cache.c | 195 +-- > fs/9p/cache.h | 25 +- > fs/9p/v9fs.c | 17 +- > fs/9p/v9fs.h | 13 +- > fs/9p/vfs_addr.c | 57 +- > fs/9p/vfs_dir.c | 13 + > fs/9p/vfs_file.c | 3 +- > fs/9p/vfs_inode.c | 26 +- > fs/9p/vfs_inode_dotl.c | 3 +- > fs/9p/vfs_super.c | 3 + > fs/afs/Kconfig | 2 +- > fs/afs/Makefile | 3 - > fs/afs/cache.c | 68 - > fs/afs/cell.c | 12 - > fs/afs/file.c | 38 +- > fs/afs/inode.c | 101 +- > fs/afs/internal.h | 37 +- > fs/afs/main.c | 14 - > fs/afs/super.c | 1 + > fs/afs/volume.c | 29 +- > fs/afs/write.c | 88 +- > fs/cachefiles/Kconfig | 7 + > fs/cachefiles/Makefile | 6 +- > fs/cachefiles/bind.c | 278 ---- > fs/cachefiles/cache.c | 378 +++++ > fs/cachefiles/daemon.c | 180 +- > fs/cachefiles/error_inject.c | 46 + > fs/cachefiles/interface.c | 747 ++++----- > fs/cachefiles/internal.h | 270 +-- > fs/cachefiles/io.c | 330 +++- > fs/cachefiles/key.c | 201 ++- > fs/cachefiles/main.c | 22 +- > fs/cachefiles/namei.c | 1223 ++++++-------- > fs/cachefiles/rdwr.c | 972 ----------- > fs/cachefiles/security.c | 2 +- > fs/cachefiles/volume.c | 139 ++ > fs/cachefiles/xattr.c | 421 ++--- > fs/ceph/Kconfig | 2 +- > fs/ceph/addr.c | 102 +- > fs/ceph/cache.c | 218 +-- > fs/ceph/cache.h | 97 +- > fs/ceph/caps.c | 3 +- > fs/ceph/file.c | 13 +- > fs/ceph/inode.c | 22 +- > fs/ceph/super.c | 10 +- > fs/ceph/super.h | 3 +- > fs/cifs/Kconfig | 2 +- > fs/cifs/Makefile | 2 +- > fs/cifs/cache.c | 105 -- > fs/cifs/cifsfs.c | 11 +- > fs/cifs/cifsglob.h | 5 +- > fs/cifs/connect.c | 12 - > fs/cifs/file.c | 64 +- > fs/cifs/fscache.c | 333 +--- > fs/cifs/fscache.h | 126 +- > fs/cifs/inode.c | 36 +- > fs/fs-writeback.c | 8 + > fs/fscache/Makefile | 6 +- > fs/fscache/cache.c | 618 +++---- > fs/fscache/cookie.c | 1448 +++++++++-------- > fs/fscache/fsdef.c | 98 -- > fs/fscache/internal.h | 317 +--- > fs/fscache/io.c | 376 ++++- > fs/fscache/main.c | 147 +- > fs/fscache/netfs.c | 74 - > fs/fscache/object.c | 1125 ------------- > fs/fscache/operation.c | 633 ------- > fs/fscache/page.c | 1242 -------------- > fs/fscache/proc.c | 47 +- > fs/fscache/stats.c | 293 +--- > fs/fscache/volume.c | 517 ++++++ > fs/namei.c | 3 +- > fs/netfs/read_helper.c | 10 +- > fs/nfs/Kconfig | 2 +- > fs/nfs/Makefile | 2 +- > fs/nfs/client.c | 4 - > fs/nfs/direct.c | 2 + > fs/nfs/file.c | 13 +- > fs/nfs/fscache-index.c | 140 -- > fs/nfs/fscache.c | 490 ++---- > fs/nfs/fscache.h | 180 +- > fs/nfs/inode.c | 11 +- > fs/nfs/nfstrace.h | 1 - > fs/nfs/read.c | 25 +- > fs/nfs/super.c | 28 +- > fs/nfs/write.c | 8 +- > include/linux/fs.h | 4 + > include/linux/fscache-cache.h | 614 ++----- > include/linux/fscache.h | 1021 +++++------- > include/linux/netfs.h | 15 +- > include/linux/nfs_fs.h | 1 - > include/linux/nfs_fs_sb.h | 9 +- > include/linux/writeback.h | 1 + > include/trace/events/cachefiles.h | 527 ++++-- > include/trace/events/fscache.h | 642 ++++---- > include/trace/events/netfs.h | 5 +- > 105 files changed, 7396 insertions(+), 13509 deletions(-) > delete mode 100644 Documentation/filesystems/caching/object.rst > delete mode 100644 Documentation/filesystems/caching/operations.rst > delete mode 100644 fs/afs/cache.c > delete mode 100644 fs/cachefiles/bind.c > create mode 100644 fs/cachefiles/cache.c > create mode 100644 fs/cachefiles/error_inject.c > delete mode 100644 fs/cachefiles/rdwr.c > create mode 100644 fs/cachefiles/volume.c > delete mode 100644 fs/cifs/cache.c > delete mode 100644 fs/fscache/fsdef.c > delete mode 100644 fs/fscache/netfs.c > delete mode 100644 fs/fscache/object.c > delete mode 100644 fs/fscache/operation.c > delete mode 100644 fs/fscache/page.c > create mode 100644 fs/fscache/volume.c > delete mode 100644 fs/nfs/fscache-index.c > > I tested these on ceph with the caches both enabled and disabled and everything looks good. Tested-by: Jeff Layton <jlayton@kernel.org>
On Wed, Dec 22, 2021 at 7:13 PM David Howells <dhowells@redhat.com> wrote: > > > Here's a set of patches implements a rewrite of the fscache driver and a > matching rewrite of the cachefiles driver, significantly simplifying the > code compared to what's upstream, removing the complex operation scheduling > and object state machine in favour of something much smaller and simpler. > > The patchset is structured such that the first few patches disable fscache > use by the network filesystems using it, remove the cachefiles driver > entirely and as much of the fscache driver as can be got away with without > causing build failures in the network filesystems. The patches after that > recreate fscache and then cachefiles, attempting to add the pieces in a > logical order. Finally, the filesystems are reenabled and then the very > last patch changes the documentation. > > > WHY REWRITE? > ============ > > Fscache's operation scheduling API was intended to handle sequencing of > cache operations, which were all required (where possible) to run > asynchronously in parallel with the operations being done by the network > filesystem, whilst allowing the cache to be brought online and offline and > to interrupt service for invalidation. > > With the advent of the tmpfile capacity in the VFS, however, an opportunity > arises to do invalidation much more simply, without having to wait for I/O > that's actually in progress: Cachefiles can simply create a tmpfile, cut > over the file pointer for the backing object attached to a cookie and > abandon the in-progress I/O, dismissing it upon completion. > > Future work here would involve using Omar Sandoval's vfs_link() with > AT_LINK_REPLACE[1] to allow an extant file to be displaced by a new hard > link from a tmpfile as currently I have to unlink the old file first. > > These patches can also simplify the object state handling as I/O operations > to the cache don't all have to be brought to a stop in order to invalidate > a file. To that end, and with an eye on to writing a new backing cache > model in the future, I've taken the opportunity to simplify the indexing > structure. > > I've separated the index cookie concept from the file cookie concept by C > type now. The former is now called a "volume cookie" (struct > fscache_volume) and there is a container of file cookies. There are then > just the two levels. All the index cookie levels are collapsed into a > single volume cookie, and this has a single printable string as a key. For > instance, an AFS volume would have a key of something like > "afs,example.com,1000555", combining the filesystem name, cell name and > volume ID. This is freeform, but must not have '/' chars in it. > > I've also eliminated all pointers back from fscache into the network > filesystem. This required the duplication of a little bit of data in the > cookie (cookie key, coherency data and file size), but it's not actually > that much. This gets rid of problems with making sure we keep netfs data > structures around so that the cache can access them. > > These patches mean that most of the code that was in the drivers before is > simply gone and those drivers are now almost entirely new code. That being > the case, there doesn't seem any particular reason to try and maintain > bisectability across it. Further, there has to be a point in the middle > where things are cut over as there's a single point everything has to go > through (ie. /dev/cachefiles) and it can't be in use by two drivers at > once. > > > ISSUES YET OUTSTANDING > ====================== > > There are some issues still outstanding, unaddressed by this patchset, that > will need fixing in future patchsets, but that don't stop this series from > being usable: > > (1) The cachefiles driver needs to stop using the backing filesystem's > metadata to store information about what parts of the cache are > populated. This is not reliable with modern extent-based filesystems. > > Fixing this is deferred to a separate patchset as it involves > negotiation with the network filesystem and the VM as to how much data > to download to fulfil a read - which brings me on to (2)... > > (2) NFS and CIFS do not take account of how the cache would like I/O to be > structured to meet its granularity requirements. Previously, the > cache used page granularity, which was fine as the network filesystems > also dealt in page granularity, and the backing filesystem (ext4, xfs > or whatever) did whatever it did out of sight. However, we now have > folios to deal with and the cache will now have to store its own > metadata to track its contents. > > The change I'm looking at making for cachefiles is to store content > bitmaps in one or more xattrs and making a bit in the map correspond > to something like a 256KiB block. However, the size of an xattr and > the fact that they have to be read/updated in one go means that I'm > looking at covering 1GiB of data per 512-byte map and storing each map > in an xattr. Cachefiles has the potential to grow into a fully > fledged filesystem of its very own if I'm not careful. > > However, I'm also looking at changing things even more radically and > going to a different model of how the cache is arranged and managed - > one that's more akin to the way, say, openafs does things - which > brings me on to (3)... > > (3) The way cachefilesd does culling is very inefficient for large caches > and it would be better to move it into the kernel if I can as > cachefilesd has to keep asking the kernel if it can cull a file. > Changing the way the backend works would allow this to be addressed. > > > BITS THAT MAY BE CONTROVERSIAL > ============================== > > There are some bits I've added that may be controversial: > > (1) I've provided a flag, S_KERNEL_FILE, that cachefiles uses to check if > a files is already being used by some other kernel service (e.g. a > duplicate cachefiles cache in the same directory) and reject it if it > is. This isn't entirely necessary, but it helps prevent accidental > data corruption. > > I don't want to use S_SWAPFILE as that has other effects, but quite > possibly swapon() should set S_KERNEL_FILE too. > > Note that it doesn't prevent userspace from interfering, though > perhaps it should. (I have made it prevent a marked directory from > being rmdir-able). > > (2) Cachefiles wants to keep the backing file for a cookie open whilst we > might need to write to it from network filesystem writeback. The > problem is that the network filesystem unuses its cookie when its file > is closed, and so we have nothing pinning the cachefiles file open and > it will get closed automatically after a short time to avoid > EMFILE/ENFILE problems. > > Reopening the cache file, however, is a problem if this is being done > due to writeback triggered by exit(). Some filesystems will oops if > we try to open a file in that context because they want to access > current->fs or suchlike. > > To get around this, I added the following: > > (A) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network > filesystem inode to indicate that we have a usage count on the > cookie caching that inode. > > (B) A flag in struct writeback_control, unpinned_fscache_wb, that is > set when __writeback_single_inode() clears the last dirty page > from i_pages - at which point it clears I_PINNING_FSCACHE_WB and > sets this flag. > > This has to be done here so that clearing I_PINNING_FSCACHE_WB can > be done atomically with the check of PAGECACHE_TAG_DIRTY that > clears I_DIRTY_PAGES. > > (C) A function, fscache_set_page_dirty(), which if it is not set, sets > I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to pin the > cache resources. > > (D) A function, fscache_unpin_writeback(), to be called by > ->write_inode() to unuse the cookie. > > (E) A function, fscache_clear_inode_writeback(), to be called when the > inode is evicted, before clear_inode() is called. This cleans up > any lingering I_PINNING_FSCACHE_WB. > > The network filesystem can then use these tools to make sure that > fscache_write_to_cache() can write locally modified data to the cache > as well as to the server. > > For the future, I'm working on write helpers for netfs lib that should > allow this facility to be removed by keeping track of the dirty > regions separately - but that's incomplete at the moment and is also > going to be affected by folios, one way or another, since it deals > with pages. > > > These patches can be found also on: > > https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-rewrite > > David > > > Changes > ======= > ver #4: > - Dropped a pair of patches to try and cope with multipage folios in > afs_write_begin/end() - it should really be done in the caller[7]. > - Fixed the use of sizeof with memset in cifs. > - Removed an extraneous kdoc param. > - Added a patch to add a tracepoint for fscache_use/unuse_cookie(). > - In cifs, tcon->vol_create_time is __le64 so doesn't need cpu_to_le64(). > - Add an expanded version of a patch to use current_is_kswapd() instead of > !gfpflags_allow_blocking()[8]. > - Removed a couple of debugging print statements. > > ver #3: > - Fixed a race in the cookie state machine between LRU discard and > relinquishment[4]. > - Fixed up the hashing to make it portable[5]. > - Fixed up some netfs coherency data to make it portable. > - Fixed some missing NFS_FSCACHE=n fallback functions in nfs[6]. > - Added a patch to store volume coherency data in an xattr. > - Added a check that the cookie is unhashed before being freed. > - Fixed fscache to use remove_proc_subtree() to remove /proc/fs/fscache/. > > ver #2: > - Fix an unused-var warning due to CONFIG_9P_FSCACHE=n. > - Use gfpflags_allow_blocking() rather than using flag directly. > - Fixed some error logging in a couple of cachefiles functions. > - Fixed an error check in the fscache volume allocation. > - Need to unmark an inode we've moved to the graveyard before unlocking. > - Upgraded to -rc4 to allow for upstream changes to cifs. > - Should only change to inval state if can get access to cache. > - Don't hold n_accesses elevated whilst cache is bound to a cookie, but > rather add a flag that prevents the state machine from being queued when > n_accesses reaches 0. > - Remove the unused cookie pointer field from the fscache_acquire > tracepoint. > - Added missing transition to LRU_DISCARDING state. > - Added two ceph patches from Jeff Layton[2]. > - Remove NFS_INO_FSCACHE as it's no longer used. > - In NFS, need to unuse a cookie on file-release, not inode-clear. > - Filled in the NFS cache I/O routines, borrowing from the previously posted > fallback I/O code[3]. > > > Link: https://lore.kernel.org/r/cover.1580251857.git.osandov@fb.com/ [1] > Link: https://lore.kernel.org/r/20211207134451.66296-1-jlayton@kernel.org/ [2] > Link: https://lore.kernel.org/r/163189108292.2509237.12615909591150927232.stgit@warthog.procyon.org.uk/ [3] > Link: https://lore.kernel.org/r/599331.1639410068@warthog.procyon.org.uk/ [4] > Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com [5] > Link: https://lore.kernel.org/r/61b90f3d.H1IkoeQfEsGNhvq9%lkp@intel.com/ [6] > Link: https://lore.kernel.org/r/CAHk-=wh2dr=NgVSVj0sw-gSuzhxhLRV5FymfPS146zGgF4kBjA@mail.gmail.com/ [7] > Link: https://lore.kernel.org/r/1638952658-20285-1-git-send-email-huangzhaoyang@gmail.com/ [8] > > > References > ========== > > These patches have been published for review before, firstly as part of a > larger set: > > Link: https://lore.kernel.org/r/158861203563.340223.7585359869938129395.stgit@warthog.procyon.org.uk/ > > Link: https://lore.kernel.org/r/159465766378.1376105.11619976251039287525.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/159465784033.1376674.18106463693989811037.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/159465821598.1377938.2046362270225008168.stgit@warthog.procyon.org.uk/ > > Link: https://lore.kernel.org/r/160588455242.3465195.3214733858273019178.stgit@warthog.procyon.org.uk/ > > Then as a cut-down set: > > Link: https://lore.kernel.org/r/161118128472.1232039.11746799833066425131.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/161161025063.2537118.2009249444682241405.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/161340385320.1303470.2392622971006879777.stgit@warthog.procyon.org.uk/ # v3 > Link: https://lore.kernel.org/r/161539526152.286939.8589700175877370401.stgit@warthog.procyon.org.uk/ # v4 > Link: https://lore.kernel.org/r/161653784755.2770958.11820491619308713741.stgit@warthog.procyon.org.uk/ # v5 > > I split out a set to just restructure the I/O, which got merged back in to > this one: > > Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/163189104510.2509237.10805032055807259087.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ # v3 > Link: https://lore.kernel.org/r/163551653404.1877519.12363794970541005441.stgit@warthog.procyon.org.uk/ # v4 > > ... and a larger set to do the conversion, also merged back into this one: > > Link: https://lore.kernel.org/r/163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/163492911924.1038219.13107463173777870713.stgit@warthog.procyon.org.uk/ # v2 > > Older versions of this one: > > Link: https://lore.kernel.org/r/163819575444.215744.318477214576928110.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/163906878733.143852.5604115678965006622.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/163967073889.1823006.12237147297060239168.stgit@warthog.procyon.org.uk/ # v3 > > Proposals/information about the design have been published here: > > Link: https://lore.kernel.org/r/24942.1573667720@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/2758811.1610621106@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/1441311.1598547738@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/160655.1611012999@warthog.procyon.org.uk/ > > And requests for information: > > Link: https://lore.kernel.org/r/3326.1579019665@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/4467.1579020509@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/3577430.1579705075@warthog.procyon.org.uk/ > > I've posted partial patches to try and help 9p and cifs along: > > Link: https://lore.kernel.org/r/1514086.1605697347@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/1794123.1605713481@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/241017.1612263863@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/270998.1612265397@warthog.procyon.org.uk/ > > --- > Dave Wysochanski (1): > nfs: Convert to new fscache volume/cookie API > > David Howells (65): > fscache, cachefiles: Disable configuration > cachefiles: Delete the cachefiles driver pending rewrite > fscache: Remove the contents of the fscache driver, pending rewrite > netfs: Display the netfs inode number in the netfs_read tracepoint > netfs: Pass a flag to ->prepare_write() to say if there's no alloc'd space > fscache: Introduce new driver > fscache: Implement a hash function > fscache: Implement cache registration > fscache: Implement volume registration > fscache: Implement cookie registration > fscache: Implement cache-level access helpers > fscache: Implement volume-level access helpers > fscache: Implement cookie-level access helpers > fscache: Implement functions add/remove a cache > fscache: Provide and use cache methods to lookup/create/free a volume > fscache: Add a function for a cache backend to note an I/O error > fscache: Implement simple cookie state machine > fscache: Implement cookie user counting and resource pinning > fscache: Implement cookie invalidation > fscache: Provide a means to begin an operation > fscache: Count data storage objects in a cache > fscache: Provide read/write stat counters for the cache > fscache: Provide a function to let the netfs update its coherency data > netfs: Pass more information on how to deal with a hole in the cache > fscache: Implement raw I/O interface > fscache: Implement higher-level write I/O interface > vfs, fscache: Implement pinning of cache usage for writeback > fscache: Provide a function to note the release of a page > fscache: Provide a function to resize a cookie > cachefiles: Introduce rewritten driver > cachefiles: Define structs > cachefiles: Add some error injection support > cachefiles: Add a couple of tracepoints for logging errors > cachefiles: Add cache error reporting macro > cachefiles: Add security derivation > cachefiles: Register a miscdev and parse commands over it > cachefiles: Provide a function to check how much space there is > vfs, cachefiles: Mark a backing file in use with an inode flag > cachefiles: Implement a function to get/create a directory in the cache > cachefiles: Implement cache registration and withdrawal > cachefiles: Implement volume support > cachefiles: Add tracepoints for calls to the VFS > cachefiles: Implement object lifecycle funcs > cachefiles: Implement key to filename encoding > cachefiles: Implement metadata/coherency data storage in xattrs > cachefiles: Mark a backing file in use with an inode flag > cachefiles: Implement culling daemon commands > cachefiles: Implement backing file wrangling > cachefiles: Implement begin and end I/O operation > cachefiles: Implement cookie resize for truncate > cachefiles: Implement the I/O routines > fscache, cachefiles: Store the volume coherency data > cachefiles: Allow cachefiles to actually function > fscache, cachefiles: Display stats of no-space events > fscache, cachefiles: Display stat of culling events > afs: Convert afs to use the new fscache API > afs: Copy local writes to the cache when writing to the server > afs: Skip truncation on the server of data we haven't written yet > 9p: Use fscache indexing rewrite and reenable caching > 9p: Copy local writes to the cache when writing to the server > nfs: Implement cache I/O by accessing the cache directly > cifs: Support fscache indexing rewrite (untested) > fscache: Rewrite documentation > fscache: Add a tracepoint for cookie use/unuse > 9p, afs, ceph, cifs, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking() > > Jeff Layton (2): > ceph: conversion to new fscache API > ceph: add fscache writeback support > > > .../filesystems/caching/backend-api.rst | 850 ++++------ > .../filesystems/caching/cachefiles.rst | 6 +- > Documentation/filesystems/caching/fscache.rst | 525 ++---- > Documentation/filesystems/caching/index.rst | 4 +- > .../filesystems/caching/netfs-api.rst | 1136 ++++--------- > Documentation/filesystems/caching/object.rst | 313 ---- > .../filesystems/caching/operations.rst | 210 --- > Documentation/filesystems/netfs_library.rst | 16 +- > fs/9p/Kconfig | 2 +- > fs/9p/cache.c | 195 +-- > fs/9p/cache.h | 25 +- > fs/9p/v9fs.c | 17 +- > fs/9p/v9fs.h | 13 +- > fs/9p/vfs_addr.c | 57 +- > fs/9p/vfs_dir.c | 13 + > fs/9p/vfs_file.c | 3 +- > fs/9p/vfs_inode.c | 26 +- > fs/9p/vfs_inode_dotl.c | 3 +- > fs/9p/vfs_super.c | 3 + > fs/afs/Kconfig | 2 +- > fs/afs/Makefile | 3 - > fs/afs/cache.c | 68 - > fs/afs/cell.c | 12 - > fs/afs/file.c | 38 +- > fs/afs/inode.c | 101 +- > fs/afs/internal.h | 37 +- > fs/afs/main.c | 14 - > fs/afs/super.c | 1 + > fs/afs/volume.c | 29 +- > fs/afs/write.c | 88 +- > fs/cachefiles/Kconfig | 7 + > fs/cachefiles/Makefile | 6 +- > fs/cachefiles/bind.c | 278 ---- > fs/cachefiles/cache.c | 378 +++++ > fs/cachefiles/daemon.c | 180 +- > fs/cachefiles/error_inject.c | 46 + > fs/cachefiles/interface.c | 747 ++++----- > fs/cachefiles/internal.h | 270 +-- > fs/cachefiles/io.c | 330 +++- > fs/cachefiles/key.c | 201 ++- > fs/cachefiles/main.c | 22 +- > fs/cachefiles/namei.c | 1223 ++++++-------- > fs/cachefiles/rdwr.c | 972 ----------- > fs/cachefiles/security.c | 2 +- > fs/cachefiles/volume.c | 139 ++ > fs/cachefiles/xattr.c | 421 ++--- > fs/ceph/Kconfig | 2 +- > fs/ceph/addr.c | 102 +- > fs/ceph/cache.c | 218 +-- > fs/ceph/cache.h | 97 +- > fs/ceph/caps.c | 3 +- > fs/ceph/file.c | 13 +- > fs/ceph/inode.c | 22 +- > fs/ceph/super.c | 10 +- > fs/ceph/super.h | 3 +- > fs/cifs/Kconfig | 2 +- > fs/cifs/Makefile | 2 +- > fs/cifs/cache.c | 105 -- > fs/cifs/cifsfs.c | 11 +- > fs/cifs/cifsglob.h | 5 +- > fs/cifs/connect.c | 12 - > fs/cifs/file.c | 64 +- > fs/cifs/fscache.c | 333 +--- > fs/cifs/fscache.h | 126 +- > fs/cifs/inode.c | 36 +- > fs/fs-writeback.c | 8 + > fs/fscache/Makefile | 6 +- > fs/fscache/cache.c | 618 +++---- > fs/fscache/cookie.c | 1448 +++++++++-------- > fs/fscache/fsdef.c | 98 -- > fs/fscache/internal.h | 317 +--- > fs/fscache/io.c | 376 ++++- > fs/fscache/main.c | 147 +- > fs/fscache/netfs.c | 74 - > fs/fscache/object.c | 1125 ------------- > fs/fscache/operation.c | 633 ------- > fs/fscache/page.c | 1242 -------------- > fs/fscache/proc.c | 47 +- > fs/fscache/stats.c | 293 +--- > fs/fscache/volume.c | 517 ++++++ > fs/namei.c | 3 +- > fs/netfs/read_helper.c | 10 +- > fs/nfs/Kconfig | 2 +- > fs/nfs/Makefile | 2 +- > fs/nfs/client.c | 4 - > fs/nfs/direct.c | 2 + > fs/nfs/file.c | 13 +- > fs/nfs/fscache-index.c | 140 -- > fs/nfs/fscache.c | 490 ++---- > fs/nfs/fscache.h | 180 +- > fs/nfs/inode.c | 11 +- > fs/nfs/nfstrace.h | 1 - > fs/nfs/read.c | 25 +- > fs/nfs/super.c | 28 +- > fs/nfs/write.c | 8 +- > include/linux/fs.h | 4 + > include/linux/fscache-cache.h | 614 ++----- > include/linux/fscache.h | 1021 +++++------- > include/linux/netfs.h | 15 +- > include/linux/nfs_fs.h | 1 - > include/linux/nfs_fs_sb.h | 9 +- > include/linux/writeback.h | 1 + > include/trace/events/cachefiles.h | 527 ++++-- > include/trace/events/fscache.h | 642 ++++---- > include/trace/events/netfs.h | 5 +- > 105 files changed, 7396 insertions(+), 13509 deletions(-) > delete mode 100644 Documentation/filesystems/caching/object.rst > delete mode 100644 Documentation/filesystems/caching/operations.rst > delete mode 100644 fs/afs/cache.c > delete mode 100644 fs/cachefiles/bind.c > create mode 100644 fs/cachefiles/cache.c > create mode 100644 fs/cachefiles/error_inject.c > delete mode 100644 fs/cachefiles/rdwr.c > create mode 100644 fs/cachefiles/volume.c > delete mode 100644 fs/cifs/cache.c > delete mode 100644 fs/fscache/fsdef.c > delete mode 100644 fs/fscache/netfs.c > delete mode 100644 fs/fscache/object.c > delete mode 100644 fs/fscache/operation.c > delete mode 100644 fs/fscache/page.c > create mode 100644 fs/fscache/volume.c > delete mode 100644 fs/nfs/fscache-index.c > > v4 passes all tests in our kafs test suite, so you can add: Tested-by: kafs-testing@auristor.com Marc
On Wed, 2021-12-22 at 23:13 +0000, David Howells wrote: > Here's a set of patches implements a rewrite of the fscache driver and a > matching rewrite of the cachefiles driver, significantly simplifying the > code compared to what's upstream, removing the complex operation scheduling > and object state machine in favour of something much smaller and simpler. > > The patchset is structured such that the first few patches disable fscache > use by the network filesystems using it, remove the cachefiles driver > entirely and as much of the fscache driver as can be got away with without > causing build failures in the network filesystems. The patches after that > recreate fscache and then cachefiles, attempting to add the pieces in a > logical order. Finally, the filesystems are reenabled and then the very > last patch changes the documentation. > > > WHY REWRITE? > ============ > > Fscache's operation scheduling API was intended to handle sequencing of > cache operations, which were all required (where possible) to run > asynchronously in parallel with the operations being done by the network > filesystem, whilst allowing the cache to be brought online and offline and > to interrupt service for invalidation. > > With the advent of the tmpfile capacity in the VFS, however, an opportunity > arises to do invalidation much more simply, without having to wait for I/O > that's actually in progress: Cachefiles can simply create a tmpfile, cut > over the file pointer for the backing object attached to a cookie and > abandon the in-progress I/O, dismissing it upon completion. > > Future work here would involve using Omar Sandoval's vfs_link() with > AT_LINK_REPLACE[1] to allow an extant file to be displaced by a new hard > link from a tmpfile as currently I have to unlink the old file first. > > These patches can also simplify the object state handling as I/O operations > to the cache don't all have to be brought to a stop in order to invalidate > a file. To that end, and with an eye on to writing a new backing cache > model in the future, I've taken the opportunity to simplify the indexing > structure. > > I've separated the index cookie concept from the file cookie concept by C > type now. The former is now called a "volume cookie" (struct > fscache_volume) and there is a container of file cookies. There are then > just the two levels. All the index cookie levels are collapsed into a > single volume cookie, and this has a single printable string as a key. For > instance, an AFS volume would have a key of something like > "afs,example.com,1000555", combining the filesystem name, cell name and > volume ID. This is freeform, but must not have '/' chars in it. > > I've also eliminated all pointers back from fscache into the network > filesystem. This required the duplication of a little bit of data in the > cookie (cookie key, coherency data and file size), but it's not actually > that much. This gets rid of problems with making sure we keep netfs data > structures around so that the cache can access them. > > These patches mean that most of the code that was in the drivers before is > simply gone and those drivers are now almost entirely new code. That being > the case, there doesn't seem any particular reason to try and maintain > bisectability across it. Further, there has to be a point in the middle > where things are cut over as there's a single point everything has to go > through (ie. /dev/cachefiles) and it can't be in use by two drivers at > once. > > > ISSUES YET OUTSTANDING > ====================== > > There are some issues still outstanding, unaddressed by this patchset, that > will need fixing in future patchsets, but that don't stop this series from > being usable: > > (1) The cachefiles driver needs to stop using the backing filesystem's > metadata to store information about what parts of the cache are > populated. This is not reliable with modern extent-based filesystems. > > Fixing this is deferred to a separate patchset as it involves > negotiation with the network filesystem and the VM as to how much data > to download to fulfil a read - which brings me on to (2)... > > (2) NFS and CIFS do not take account of how the cache would like I/O to be > structured to meet its granularity requirements. Previously, the > cache used page granularity, which was fine as the network filesystems > also dealt in page granularity, and the backing filesystem (ext4, xfs > or whatever) did whatever it did out of sight. However, we now have > folios to deal with and the cache will now have to store its own > metadata to track its contents. > > The change I'm looking at making for cachefiles is to store content > bitmaps in one or more xattrs and making a bit in the map correspond > to something like a 256KiB block. However, the size of an xattr and > the fact that they have to be read/updated in one go means that I'm > looking at covering 1GiB of data per 512-byte map and storing each map > in an xattr. Cachefiles has the potential to grow into a fully > fledged filesystem of its very own if I'm not careful. > > However, I'm also looking at changing things even more radically and > going to a different model of how the cache is arranged and managed - > one that's more akin to the way, say, openafs does things - which > brings me on to (3)... > > (3) The way cachefilesd does culling is very inefficient for large caches > and it would be better to move it into the kernel if I can as > cachefilesd has to keep asking the kernel if it can cull a file. > Changing the way the backend works would allow this to be addressed. > > > BITS THAT MAY BE CONTROVERSIAL > ============================== > > There are some bits I've added that may be controversial: > > (1) I've provided a flag, S_KERNEL_FILE, that cachefiles uses to check if > a files is already being used by some other kernel service (e.g. a > duplicate cachefiles cache in the same directory) and reject it if it > is. This isn't entirely necessary, but it helps prevent accidental > data corruption. > > I don't want to use S_SWAPFILE as that has other effects, but quite > possibly swapon() should set S_KERNEL_FILE too. > > Note that it doesn't prevent userspace from interfering, though > perhaps it should. (I have made it prevent a marked directory from > being rmdir-able). > > (2) Cachefiles wants to keep the backing file for a cookie open whilst we > might need to write to it from network filesystem writeback. The > problem is that the network filesystem unuses its cookie when its file > is closed, and so we have nothing pinning the cachefiles file open and > it will get closed automatically after a short time to avoid > EMFILE/ENFILE problems. > > Reopening the cache file, however, is a problem if this is being done > due to writeback triggered by exit(). Some filesystems will oops if > we try to open a file in that context because they want to access > current->fs or suchlike. > > To get around this, I added the following: > > (A) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network > filesystem inode to indicate that we have a usage count on the > cookie caching that inode. > > (B) A flag in struct writeback_control, unpinned_fscache_wb, that is > set when __writeback_single_inode() clears the last dirty page > from i_pages - at which point it clears I_PINNING_FSCACHE_WB and > sets this flag. > > This has to be done here so that clearing I_PINNING_FSCACHE_WB can > be done atomically with the check of PAGECACHE_TAG_DIRTY that > clears I_DIRTY_PAGES. > > (C) A function, fscache_set_page_dirty(), which if it is not set, sets > I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to pin the > cache resources. > > (D) A function, fscache_unpin_writeback(), to be called by > ->write_inode() to unuse the cookie. > > (E) A function, fscache_clear_inode_writeback(), to be called when the > inode is evicted, before clear_inode() is called. This cleans up > any lingering I_PINNING_FSCACHE_WB. > > The network filesystem can then use these tools to make sure that > fscache_write_to_cache() can write locally modified data to the cache > as well as to the server. > > For the future, I'm working on write helpers for netfs lib that should > allow this facility to be removed by keeping track of the dirty > regions separately - but that's incomplete at the moment and is also > going to be affected by folios, one way or another, since it deals > with pages. > > > These patches can be found also on: > > https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-rewrite > > David > > > Changes > ======= > ver #4: > - Dropped a pair of patches to try and cope with multipage folios in > afs_write_begin/end() - it should really be done in the caller[7]. > - Fixed the use of sizeof with memset in cifs. > - Removed an extraneous kdoc param. > - Added a patch to add a tracepoint for fscache_use/unuse_cookie(). > - In cifs, tcon->vol_create_time is __le64 so doesn't need cpu_to_le64(). > - Add an expanded version of a patch to use current_is_kswapd() instead of > !gfpflags_allow_blocking()[8]. > - Removed a couple of debugging print statements. > > ver #3: > - Fixed a race in the cookie state machine between LRU discard and > relinquishment[4]. > - Fixed up the hashing to make it portable[5]. > - Fixed up some netfs coherency data to make it portable. > - Fixed some missing NFS_FSCACHE=n fallback functions in nfs[6]. > - Added a patch to store volume coherency data in an xattr. > - Added a check that the cookie is unhashed before being freed. > - Fixed fscache to use remove_proc_subtree() to remove /proc/fs/fscache/. > > ver #2: > - Fix an unused-var warning due to CONFIG_9P_FSCACHE=n. > - Use gfpflags_allow_blocking() rather than using flag directly. > - Fixed some error logging in a couple of cachefiles functions. > - Fixed an error check in the fscache volume allocation. > - Need to unmark an inode we've moved to the graveyard before unlocking. > - Upgraded to -rc4 to allow for upstream changes to cifs. > - Should only change to inval state if can get access to cache. > - Don't hold n_accesses elevated whilst cache is bound to a cookie, but > rather add a flag that prevents the state machine from being queued when > n_accesses reaches 0. > - Remove the unused cookie pointer field from the fscache_acquire > tracepoint. > - Added missing transition to LRU_DISCARDING state. > - Added two ceph patches from Jeff Layton[2]. > - Remove NFS_INO_FSCACHE as it's no longer used. > - In NFS, need to unuse a cookie on file-release, not inode-clear. > - Filled in the NFS cache I/O routines, borrowing from the previously posted > fallback I/O code[3]. > > > Link: https://lore.kernel.org/r/cover.1580251857.git.osandov@fb.com/ [1] > Link: https://lore.kernel.org/r/20211207134451.66296-1-jlayton@kernel.org/ [2] > Link: https://lore.kernel.org/r/163189108292.2509237.12615909591150927232.stgit@warthog.procyon.org.uk/ [3] > Link: https://lore.kernel.org/r/599331.1639410068@warthog.procyon.org.uk/ [4] > Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com [5] > Link: https://lore.kernel.org/r/61b90f3d.H1IkoeQfEsGNhvq9%lkp@intel.com/ [6] > Link: https://lore.kernel.org/r/CAHk-=wh2dr=NgVSVj0sw-gSuzhxhLRV5FymfPS146zGgF4kBjA@mail.gmail.com/ [7] > Link: https://lore.kernel.org/r/1638952658-20285-1-git-send-email-huangzhaoyang@gmail.com/ [8] > > > References > ========== > > These patches have been published for review before, firstly as part of a > larger set: > > Link: https://lore.kernel.org/r/158861203563.340223.7585359869938129395.stgit@warthog.procyon.org.uk/ > > Link: https://lore.kernel.org/r/159465766378.1376105.11619976251039287525.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/159465784033.1376674.18106463693989811037.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/159465821598.1377938.2046362270225008168.stgit@warthog.procyon.org.uk/ > > Link: https://lore.kernel.org/r/160588455242.3465195.3214733858273019178.stgit@warthog.procyon.org.uk/ > > Then as a cut-down set: > > Link: https://lore.kernel.org/r/161118128472.1232039.11746799833066425131.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/161161025063.2537118.2009249444682241405.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/161340385320.1303470.2392622971006879777.stgit@warthog.procyon.org.uk/ # v3 > Link: https://lore.kernel.org/r/161539526152.286939.8589700175877370401.stgit@warthog.procyon.org.uk/ # v4 > Link: https://lore.kernel.org/r/161653784755.2770958.11820491619308713741.stgit@warthog.procyon.org.uk/ # v5 > > I split out a set to just restructure the I/O, which got merged back in to > this one: > > Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/163189104510.2509237.10805032055807259087.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ # v3 > Link: https://lore.kernel.org/r/163551653404.1877519.12363794970541005441.stgit@warthog.procyon.org.uk/ # v4 > > ... and a larger set to do the conversion, also merged back into this one: > > Link: https://lore.kernel.org/r/163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/163492911924.1038219.13107463173777870713.stgit@warthog.procyon.org.uk/ # v2 > > Older versions of this one: > > Link: https://lore.kernel.org/r/163819575444.215744.318477214576928110.stgit@warthog.procyon.org.uk/ # v1 > Link: https://lore.kernel.org/r/163906878733.143852.5604115678965006622.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/163967073889.1823006.12237147297060239168.stgit@warthog.procyon.org.uk/ # v3 > > Proposals/information about the design have been published here: > > Link: https://lore.kernel.org/r/24942.1573667720@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/2758811.1610621106@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/1441311.1598547738@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/160655.1611012999@warthog.procyon.org.uk/ > > And requests for information: > > Link: https://lore.kernel.org/r/3326.1579019665@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/4467.1579020509@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/3577430.1579705075@warthog.procyon.org.uk/ > > I've posted partial patches to try and help 9p and cifs along: > > Link: https://lore.kernel.org/r/1514086.1605697347@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/1794123.1605713481@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/241017.1612263863@warthog.procyon.org.uk/ > Link: https://lore.kernel.org/r/270998.1612265397@warthog.procyon.org.uk/ > > --- > Dave Wysochanski (1): > nfs: Convert to new fscache volume/cookie API > > David Howells (65): > fscache, cachefiles: Disable configuration > cachefiles: Delete the cachefiles driver pending rewrite > fscache: Remove the contents of the fscache driver, pending rewrite > netfs: Display the netfs inode number in the netfs_read tracepoint > netfs: Pass a flag to ->prepare_write() to say if there's no alloc'd space > fscache: Introduce new driver > fscache: Implement a hash function > fscache: Implement cache registration > fscache: Implement volume registration > fscache: Implement cookie registration > fscache: Implement cache-level access helpers > fscache: Implement volume-level access helpers > fscache: Implement cookie-level access helpers > fscache: Implement functions add/remove a cache > fscache: Provide and use cache methods to lookup/create/free a volume > fscache: Add a function for a cache backend to note an I/O error > fscache: Implement simple cookie state machine > fscache: Implement cookie user counting and resource pinning > fscache: Implement cookie invalidation > fscache: Provide a means to begin an operation > fscache: Count data storage objects in a cache > fscache: Provide read/write stat counters for the cache > fscache: Provide a function to let the netfs update its coherency data > netfs: Pass more information on how to deal with a hole in the cache > fscache: Implement raw I/O interface > fscache: Implement higher-level write I/O interface > vfs, fscache: Implement pinning of cache usage for writeback > fscache: Provide a function to note the release of a page > fscache: Provide a function to resize a cookie > cachefiles: Introduce rewritten driver > cachefiles: Define structs > cachefiles: Add some error injection support > cachefiles: Add a couple of tracepoints for logging errors > cachefiles: Add cache error reporting macro > cachefiles: Add security derivation > cachefiles: Register a miscdev and parse commands over it > cachefiles: Provide a function to check how much space there is > vfs, cachefiles: Mark a backing file in use with an inode flag > cachefiles: Implement a function to get/create a directory in the cache > cachefiles: Implement cache registration and withdrawal > cachefiles: Implement volume support > cachefiles: Add tracepoints for calls to the VFS > cachefiles: Implement object lifecycle funcs > cachefiles: Implement key to filename encoding > cachefiles: Implement metadata/coherency data storage in xattrs > cachefiles: Mark a backing file in use with an inode flag > cachefiles: Implement culling daemon commands > cachefiles: Implement backing file wrangling > cachefiles: Implement begin and end I/O operation > cachefiles: Implement cookie resize for truncate > cachefiles: Implement the I/O routines > fscache, cachefiles: Store the volume coherency data > cachefiles: Allow cachefiles to actually function > fscache, cachefiles: Display stats of no-space events > fscache, cachefiles: Display stat of culling events > afs: Convert afs to use the new fscache API > afs: Copy local writes to the cache when writing to the server > afs: Skip truncation on the server of data we haven't written yet > 9p: Use fscache indexing rewrite and reenable caching > 9p: Copy local writes to the cache when writing to the server > nfs: Implement cache I/O by accessing the cache directly > cifs: Support fscache indexing rewrite (untested) > fscache: Rewrite documentation > fscache: Add a tracepoint for cookie use/unuse > 9p, afs, ceph, cifs, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking() > > Jeff Layton (2): > ceph: conversion to new fscache API > ceph: add fscache writeback support > > > .../filesystems/caching/backend-api.rst | 850 ++++------ > .../filesystems/caching/cachefiles.rst | 6 +- > Documentation/filesystems/caching/fscache.rst | 525 ++---- > Documentation/filesystems/caching/index.rst | 4 +- > .../filesystems/caching/netfs-api.rst | 1136 ++++--------- > Documentation/filesystems/caching/object.rst | 313 ---- > .../filesystems/caching/operations.rst | 210 --- > Documentation/filesystems/netfs_library.rst | 16 +- > fs/9p/Kconfig | 2 +- > fs/9p/cache.c | 195 +-- > fs/9p/cache.h | 25 +- > fs/9p/v9fs.c | 17 +- > fs/9p/v9fs.h | 13 +- > fs/9p/vfs_addr.c | 57 +- > fs/9p/vfs_dir.c | 13 + > fs/9p/vfs_file.c | 3 +- > fs/9p/vfs_inode.c | 26 +- > fs/9p/vfs_inode_dotl.c | 3 +- > fs/9p/vfs_super.c | 3 + > fs/afs/Kconfig | 2 +- > fs/afs/Makefile | 3 - > fs/afs/cache.c | 68 - > fs/afs/cell.c | 12 - > fs/afs/file.c | 38 +- > fs/afs/inode.c | 101 +- > fs/afs/internal.h | 37 +- > fs/afs/main.c | 14 - > fs/afs/super.c | 1 + > fs/afs/volume.c | 29 +- > fs/afs/write.c | 88 +- > fs/cachefiles/Kconfig | 7 + > fs/cachefiles/Makefile | 6 +- > fs/cachefiles/bind.c | 278 ---- > fs/cachefiles/cache.c | 378 +++++ > fs/cachefiles/daemon.c | 180 +- > fs/cachefiles/error_inject.c | 46 + > fs/cachefiles/interface.c | 747 ++++----- > fs/cachefiles/internal.h | 270 +-- > fs/cachefiles/io.c | 330 +++- > fs/cachefiles/key.c | 201 ++- > fs/cachefiles/main.c | 22 +- > fs/cachefiles/namei.c | 1223 ++++++-------- > fs/cachefiles/rdwr.c | 972 ----------- > fs/cachefiles/security.c | 2 +- > fs/cachefiles/volume.c | 139 ++ > fs/cachefiles/xattr.c | 421 ++--- > fs/ceph/Kconfig | 2 +- > fs/ceph/addr.c | 102 +- > fs/ceph/cache.c | 218 +-- > fs/ceph/cache.h | 97 +- > fs/ceph/caps.c | 3 +- > fs/ceph/file.c | 13 +- > fs/ceph/inode.c | 22 +- > fs/ceph/super.c | 10 +- > fs/ceph/super.h | 3 +- > fs/cifs/Kconfig | 2 +- > fs/cifs/Makefile | 2 +- > fs/cifs/cache.c | 105 -- > fs/cifs/cifsfs.c | 11 +- > fs/cifs/cifsglob.h | 5 +- > fs/cifs/connect.c | 12 - > fs/cifs/file.c | 64 +- > fs/cifs/fscache.c | 333 +--- > fs/cifs/fscache.h | 126 +- > fs/cifs/inode.c | 36 +- > fs/fs-writeback.c | 8 + > fs/fscache/Makefile | 6 +- > fs/fscache/cache.c | 618 +++---- > fs/fscache/cookie.c | 1448 +++++++++-------- > fs/fscache/fsdef.c | 98 -- > fs/fscache/internal.h | 317 +--- > fs/fscache/io.c | 376 ++++- > fs/fscache/main.c | 147 +- > fs/fscache/netfs.c | 74 - > fs/fscache/object.c | 1125 ------------- > fs/fscache/operation.c | 633 ------- > fs/fscache/page.c | 1242 -------------- > fs/fscache/proc.c | 47 +- > fs/fscache/stats.c | 293 +--- > fs/fscache/volume.c | 517 ++++++ > fs/namei.c | 3 +- > fs/netfs/read_helper.c | 10 +- > fs/nfs/Kconfig | 2 +- > fs/nfs/Makefile | 2 +- > fs/nfs/client.c | 4 - > fs/nfs/direct.c | 2 + > fs/nfs/file.c | 13 +- > fs/nfs/fscache-index.c | 140 -- > fs/nfs/fscache.c | 490 ++---- > fs/nfs/fscache.h | 180 +- > fs/nfs/inode.c | 11 +- > fs/nfs/nfstrace.h | 1 - > fs/nfs/read.c | 25 +- > fs/nfs/super.c | 28 +- > fs/nfs/write.c | 8 +- > include/linux/fs.h | 4 + > include/linux/fscache-cache.h | 614 ++----- > include/linux/fscache.h | 1021 +++++------- > include/linux/netfs.h | 15 +- > include/linux/nfs_fs.h | 1 - > include/linux/nfs_fs_sb.h | 9 +- > include/linux/writeback.h | 1 + > include/trace/events/cachefiles.h | 527 ++++-- > include/trace/events/fscache.h | 642 ++++---- > include/trace/events/netfs.h | 5 +- > 105 files changed, 7396 insertions(+), 13509 deletions(-) > delete mode 100644 Documentation/filesystems/caching/object.rst > delete mode 100644 Documentation/filesystems/caching/operations.rst > delete mode 100644 fs/afs/cache.c > delete mode 100644 fs/cachefiles/bind.c > create mode 100644 fs/cachefiles/cache.c > create mode 100644 fs/cachefiles/error_inject.c > delete mode 100644 fs/cachefiles/rdwr.c > create mode 100644 fs/cachefiles/volume.c > delete mode 100644 fs/cifs/cache.c > delete mode 100644 fs/fscache/fsdef.c > delete mode 100644 fs/fscache/netfs.c > delete mode 100644 fs/fscache/object.c > delete mode 100644 fs/fscache/operation.c > delete mode 100644 fs/fscache/page.c > create mode 100644 fs/fscache/volume.c > delete mode 100644 fs/nfs/fscache-index.c > > Whew, big set, but it looks good overall. I had a few nit-picky comments, but I'm fine with fixing those up in follow-on patches so that we don't invalidate any testing done so far. You can add my Reviewed-by to patches 1-55 and 66-68. For 56-63, you can add my Acked-by. I'm less familiar with those filesystems these days, but they seem sane. Nice work!
David Howells wrote on Wed, Dec 22, 2021 at 11:13:11PM +0000: > These patches can be found also on: > > https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-rewrite Tested today's tip of the branch for 9p, with the patch I just sent it appears to work ok with the note that files aren't read from cachefilesd properly. They were in v5.15 and not 5.16 so it's another regression from the previous PR, and not a problem with these patches though, so can add my tested-by to the three 9p patches: Tested-by: Dominique Martinet <asmadeus@codewreck.org>
Here's a set of patches implements a rewrite of the fscache driver and a matching rewrite of the cachefiles driver, significantly simplifying the code compared to what's upstream, removing the complex operation scheduling and object state machine in favour of something much smaller and simpler. The patchset is structured such that the first few patches disable fscache use by the network filesystems using it, remove the cachefiles driver entirely and as much of the fscache driver as can be got away with without causing build failures in the network filesystems. The patches after that recreate fscache and then cachefiles, attempting to add the pieces in a logical order. Finally, the filesystems are reenabled and then the very last patch changes the documentation. WHY REWRITE? ============ Fscache's operation scheduling API was intended to handle sequencing of cache operations, which were all required (where possible) to run asynchronously in parallel with the operations being done by the network filesystem, whilst allowing the cache to be brought online and offline and to interrupt service for invalidation. With the advent of the tmpfile capacity in the VFS, however, an opportunity arises to do invalidation much more simply, without having to wait for I/O that's actually in progress: Cachefiles can simply create a tmpfile, cut over the file pointer for the backing object attached to a cookie and abandon the in-progress I/O, dismissing it upon completion. Future work here would involve using Omar Sandoval's vfs_link() with AT_LINK_REPLACE[1] to allow an extant file to be displaced by a new hard link from a tmpfile as currently I have to unlink the old file first. These patches can also simplify the object state handling as I/O operations to the cache don't all have to be brought to a stop in order to invalidate a file. To that end, and with an eye on to writing a new backing cache model in the future, I've taken the opportunity to simplify the indexing structure. I've separated the index cookie concept from the file cookie concept by C type now. The former is now called a "volume cookie" (struct fscache_volume) and there is a container of file cookies. There are then just the two levels. All the index cookie levels are collapsed into a single volume cookie, and this has a single printable string as a key. For instance, an AFS volume would have a key of something like "afs,example.com,1000555", combining the filesystem name, cell name and volume ID. This is freeform, but must not have '/' chars in it. I've also eliminated all pointers back from fscache into the network filesystem. This required the duplication of a little bit of data in the cookie (cookie key, coherency data and file size), but it's not actually that much. This gets rid of problems with making sure we keep netfs data structures around so that the cache can access them. These patches mean that most of the code that was in the drivers before is simply gone and those drivers are now almost entirely new code. That being the case, there doesn't seem any particular reason to try and maintain bisectability across it. Further, there has to be a point in the middle where things are cut over as there's a single point everything has to go through (ie. /dev/cachefiles) and it can't be in use by two drivers at once. ISSUES YET OUTSTANDING ====================== There are some issues still outstanding, unaddressed by this patchset, that will need fixing in future patchsets, but that don't stop this series from being usable: (1) The cachefiles driver needs to stop using the backing filesystem's metadata to store information about what parts of the cache are populated. This is not reliable with modern extent-based filesystems. Fixing this is deferred to a separate patchset as it involves negotiation with the network filesystem and the VM as to how much data to download to fulfil a read - which brings me on to (2)... (2) NFS and CIFS do not take account of how the cache would like I/O to be structured to meet its granularity requirements. Previously, the cache used page granularity, which was fine as the network filesystems also dealt in page granularity, and the backing filesystem (ext4, xfs or whatever) did whatever it did out of sight. However, we now have folios to deal with and the cache will now have to store its own metadata to track its contents. The change I'm looking at making for cachefiles is to store content bitmaps in one or more xattrs and making a bit in the map correspond to something like a 256KiB block. However, the size of an xattr and the fact that they have to be read/updated in one go means that I'm looking at covering 1GiB of data per 512-byte map and storing each map in an xattr. Cachefiles has the potential to grow into a fully fledged filesystem of its very own if I'm not careful. However, I'm also looking at changing things even more radically and going to a different model of how the cache is arranged and managed - one that's more akin to the way, say, openafs does things - which brings me on to (3)... (3) The way cachefilesd does culling is very inefficient for large caches and it would be better to move it into the kernel if I can as cachefilesd has to keep asking the kernel if it can cull a file. Changing the way the backend works would allow this to be addressed. BITS THAT MAY BE CONTROVERSIAL ============================== There are some bits I've added that may be controversial: (1) I've provided a flag, S_KERNEL_FILE, that cachefiles uses to check if a files is already being used by some other kernel service (e.g. a duplicate cachefiles cache in the same directory) and reject it if it is. This isn't entirely necessary, but it helps prevent accidental data corruption. I don't want to use S_SWAPFILE as that has other effects, but quite possibly swapon() should set S_KERNEL_FILE too. Note that it doesn't prevent userspace from interfering, though perhaps it should. (I have made it prevent a marked directory from being rmdir-able). (2) Cachefiles wants to keep the backing file for a cookie open whilst we might need to write to it from network filesystem writeback. The problem is that the network filesystem unuses its cookie when its file is closed, and so we have nothing pinning the cachefiles file open and it will get closed automatically after a short time to avoid EMFILE/ENFILE problems. Reopening the cache file, however, is a problem if this is being done due to writeback triggered by exit(). Some filesystems will oops if we try to open a file in that context because they want to access current->fs or suchlike. To get around this, I added the following: (A) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network filesystem inode to indicate that we have a usage count on the cookie caching that inode. (B) A flag in struct writeback_control, unpinned_fscache_wb, that is set when __writeback_single_inode() clears the last dirty page from i_pages - at which point it clears I_PINNING_FSCACHE_WB and sets this flag. This has to be done here so that clearing I_PINNING_FSCACHE_WB can be done atomically with the check of PAGECACHE_TAG_DIRTY that clears I_DIRTY_PAGES. (C) A function, fscache_set_page_dirty(), which if it is not set, sets I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to pin the cache resources. (D) A function, fscache_unpin_writeback(), to be called by ->write_inode() to unuse the cookie. (E) A function, fscache_clear_inode_writeback(), to be called when the inode is evicted, before clear_inode() is called. This cleans up any lingering I_PINNING_FSCACHE_WB. The network filesystem can then use these tools to make sure that fscache_write_to_cache() can write locally modified data to the cache as well as to the server. For the future, I'm working on write helpers for netfs lib that should allow this facility to be removed by keeping track of the dirty regions separately - but that's incomplete at the moment and is also going to be affected by folios, one way or another, since it deals with pages. These patches can be found also on: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-rewrite David Changes ======= ver #4: - Dropped a pair of patches to try and cope with multipage folios in afs_write_begin/end() - it should really be done in the caller[7]. - Fixed the use of sizeof with memset in cifs. - Removed an extraneous kdoc param. - Added a patch to add a tracepoint for fscache_use/unuse_cookie(). - In cifs, tcon->vol_create_time is __le64 so doesn't need cpu_to_le64(). - Add an expanded version of a patch to use current_is_kswapd() instead of !gfpflags_allow_blocking()[8]. - Removed a couple of debugging print statements. ver #3: - Fixed a race in the cookie state machine between LRU discard and relinquishment[4]. - Fixed up the hashing to make it portable[5]. - Fixed up some netfs coherency data to make it portable. - Fixed some missing NFS_FSCACHE=n fallback functions in nfs[6]. - Added a patch to store volume coherency data in an xattr. - Added a check that the cookie is unhashed before being freed. - Fixed fscache to use remove_proc_subtree() to remove /proc/fs/fscache/. ver #2: - Fix an unused-var warning due to CONFIG_9P_FSCACHE=n. - Use gfpflags_allow_blocking() rather than using flag directly. - Fixed some error logging in a couple of cachefiles functions. - Fixed an error check in the fscache volume allocation. - Need to unmark an inode we've moved to the graveyard before unlocking. - Upgraded to -rc4 to allow for upstream changes to cifs. - Should only change to inval state if can get access to cache. - Don't hold n_accesses elevated whilst cache is bound to a cookie, but rather add a flag that prevents the state machine from being queued when n_accesses reaches 0. - Remove the unused cookie pointer field from the fscache_acquire tracepoint. - Added missing transition to LRU_DISCARDING state. - Added two ceph patches from Jeff Layton[2]. - Remove NFS_INO_FSCACHE as it's no longer used. - In NFS, need to unuse a cookie on file-release, not inode-clear. - Filled in the NFS cache I/O routines, borrowing from the previously posted fallback I/O code[3]. Link: https://lore.kernel.org/r/cover.1580251857.git.osandov@fb.com/ [1] Link: https://lore.kernel.org/r/20211207134451.66296-1-jlayton@kernel.org/ [2] Link: https://lore.kernel.org/r/163189108292.2509237.12615909591150927232.stgit@warthog.procyon.org.uk/ [3] Link: https://lore.kernel.org/r/599331.1639410068@warthog.procyon.org.uk/ [4] Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com [5] Link: https://lore.kernel.org/r/61b90f3d.H1IkoeQfEsGNhvq9%lkp@intel.com/ [6] Link: https://lore.kernel.org/r/CAHk-=wh2dr=NgVSVj0sw-gSuzhxhLRV5FymfPS146zGgF4kBjA@mail.gmail.com/ [7] Link: https://lore.kernel.org/r/1638952658-20285-1-git-send-email-huangzhaoyang@gmail.com/ [8] References ========== These patches have been published for review before, firstly as part of a larger set: Link: https://lore.kernel.org/r/158861203563.340223.7585359869938129395.stgit@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/159465766378.1376105.11619976251039287525.stgit@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/159465784033.1376674.18106463693989811037.stgit@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/159465821598.1377938.2046362270225008168.stgit@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/160588455242.3465195.3214733858273019178.stgit@warthog.procyon.org.uk/ Then as a cut-down set: Link: https://lore.kernel.org/r/161118128472.1232039.11746799833066425131.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/161161025063.2537118.2009249444682241405.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/161340385320.1303470.2392622971006879777.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/161539526152.286939.8589700175877370401.stgit@warthog.procyon.org.uk/ # v4 Link: https://lore.kernel.org/r/161653784755.2770958.11820491619308713741.stgit@warthog.procyon.org.uk/ # v5 I split out a set to just restructure the I/O, which got merged back in to this one: Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/163189104510.2509237.10805032055807259087.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/163551653404.1877519.12363794970541005441.stgit@warthog.procyon.org.uk/ # v4 ... and a larger set to do the conversion, also merged back into this one: Link: https://lore.kernel.org/r/163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163492911924.1038219.13107463173777870713.stgit@warthog.procyon.org.uk/ # v2 Older versions of this one: Link: https://lore.kernel.org/r/163819575444.215744.318477214576928110.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906878733.143852.5604115678965006622.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967073889.1823006.12237147297060239168.stgit@warthog.procyon.org.uk/ # v3 Proposals/information about the design have been published here: Link: https://lore.kernel.org/r/24942.1573667720@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/2758811.1610621106@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/1441311.1598547738@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/160655.1611012999@warthog.procyon.org.uk/ And requests for information: Link: https://lore.kernel.org/r/3326.1579019665@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/4467.1579020509@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/3577430.1579705075@warthog.procyon.org.uk/ I've posted partial patches to try and help 9p and cifs along: Link: https://lore.kernel.org/r/1514086.1605697347@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/1794123.1605713481@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/241017.1612263863@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/270998.1612265397@warthog.procyon.org.uk/ --- Dave Wysochanski (1): nfs: Convert to new fscache volume/cookie API David Howells (65): fscache, cachefiles: Disable configuration cachefiles: Delete the cachefiles driver pending rewrite fscache: Remove the contents of the fscache driver, pending rewrite netfs: Display the netfs inode number in the netfs_read tracepoint netfs: Pass a flag to ->prepare_write() to say if there's no alloc'd space fscache: Introduce new driver fscache: Implement a hash function fscache: Implement cache registration fscache: Implement volume registration fscache: Implement cookie registration fscache: Implement cache-level access helpers fscache: Implement volume-level access helpers fscache: Implement cookie-level access helpers fscache: Implement functions add/remove a cache fscache: Provide and use cache methods to lookup/create/free a volume fscache: Add a function for a cache backend to note an I/O error fscache: Implement simple cookie state machine fscache: Implement cookie user counting and resource pinning fscache: Implement cookie invalidation fscache: Provide a means to begin an operation fscache: Count data storage objects in a cache fscache: Provide read/write stat counters for the cache fscache: Provide a function to let the netfs update its coherency data netfs: Pass more information on how to deal with a hole in the cache fscache: Implement raw I/O interface fscache: Implement higher-level write I/O interface vfs, fscache: Implement pinning of cache usage for writeback fscache: Provide a function to note the release of a page fscache: Provide a function to resize a cookie cachefiles: Introduce rewritten driver cachefiles: Define structs cachefiles: Add some error injection support cachefiles: Add a couple of tracepoints for logging errors cachefiles: Add cache error reporting macro cachefiles: Add security derivation cachefiles: Register a miscdev and parse commands over it cachefiles: Provide a function to check how much space there is vfs, cachefiles: Mark a backing file in use with an inode flag cachefiles: Implement a function to get/create a directory in the cache cachefiles: Implement cache registration and withdrawal cachefiles: Implement volume support cachefiles: Add tracepoints for calls to the VFS cachefiles: Implement object lifecycle funcs cachefiles: Implement key to filename encoding cachefiles: Implement metadata/coherency data storage in xattrs cachefiles: Mark a backing file in use with an inode flag cachefiles: Implement culling daemon commands cachefiles: Implement backing file wrangling cachefiles: Implement begin and end I/O operation cachefiles: Implement cookie resize for truncate cachefiles: Implement the I/O routines fscache, cachefiles: Store the volume coherency data cachefiles: Allow cachefiles to actually function fscache, cachefiles: Display stats of no-space events fscache, cachefiles: Display stat of culling events afs: Convert afs to use the new fscache API afs: Copy local writes to the cache when writing to the server afs: Skip truncation on the server of data we haven't written yet 9p: Use fscache indexing rewrite and reenable caching 9p: Copy local writes to the cache when writing to the server nfs: Implement cache I/O by accessing the cache directly cifs: Support fscache indexing rewrite (untested) fscache: Rewrite documentation fscache: Add a tracepoint for cookie use/unuse 9p, afs, ceph, cifs, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking() Jeff Layton (2): ceph: conversion to new fscache API ceph: add fscache writeback support .../filesystems/caching/backend-api.rst | 850 ++++------ .../filesystems/caching/cachefiles.rst | 6 +- Documentation/filesystems/caching/fscache.rst | 525 ++---- Documentation/filesystems/caching/index.rst | 4 +- .../filesystems/caching/netfs-api.rst | 1136 ++++--------- Documentation/filesystems/caching/object.rst | 313 ---- .../filesystems/caching/operations.rst | 210 --- Documentation/filesystems/netfs_library.rst | 16 +- fs/9p/Kconfig | 2 +- fs/9p/cache.c | 195 +-- fs/9p/cache.h | 25 +- fs/9p/v9fs.c | 17 +- fs/9p/v9fs.h | 13 +- fs/9p/vfs_addr.c | 57 +- fs/9p/vfs_dir.c | 13 + fs/9p/vfs_file.c | 3 +- fs/9p/vfs_inode.c | 26 +- fs/9p/vfs_inode_dotl.c | 3 +- fs/9p/vfs_super.c | 3 + fs/afs/Kconfig | 2 +- fs/afs/Makefile | 3 - fs/afs/cache.c | 68 - fs/afs/cell.c | 12 - fs/afs/file.c | 38 +- fs/afs/inode.c | 101 +- fs/afs/internal.h | 37 +- fs/afs/main.c | 14 - fs/afs/super.c | 1 + fs/afs/volume.c | 29 +- fs/afs/write.c | 88 +- fs/cachefiles/Kconfig | 7 + fs/cachefiles/Makefile | 6 +- fs/cachefiles/bind.c | 278 ---- fs/cachefiles/cache.c | 378 +++++ fs/cachefiles/daemon.c | 180 +- fs/cachefiles/error_inject.c | 46 + fs/cachefiles/interface.c | 747 ++++----- fs/cachefiles/internal.h | 270 +-- fs/cachefiles/io.c | 330 +++- fs/cachefiles/key.c | 201 ++- fs/cachefiles/main.c | 22 +- fs/cachefiles/namei.c | 1223 ++++++-------- fs/cachefiles/rdwr.c | 972 ----------- fs/cachefiles/security.c | 2 +- fs/cachefiles/volume.c | 139 ++ fs/cachefiles/xattr.c | 421 ++--- fs/ceph/Kconfig | 2 +- fs/ceph/addr.c | 102 +- fs/ceph/cache.c | 218 +-- fs/ceph/cache.h | 97 +- fs/ceph/caps.c | 3 +- fs/ceph/file.c | 13 +- fs/ceph/inode.c | 22 +- fs/ceph/super.c | 10 +- fs/ceph/super.h | 3 +- fs/cifs/Kconfig | 2 +- fs/cifs/Makefile | 2 +- fs/cifs/cache.c | 105 -- fs/cifs/cifsfs.c | 11 +- fs/cifs/cifsglob.h | 5 +- fs/cifs/connect.c | 12 - fs/cifs/file.c | 64 +- fs/cifs/fscache.c | 333 +--- fs/cifs/fscache.h | 126 +- fs/cifs/inode.c | 36 +- fs/fs-writeback.c | 8 + fs/fscache/Makefile | 6 +- fs/fscache/cache.c | 618 +++---- fs/fscache/cookie.c | 1448 +++++++++-------- fs/fscache/fsdef.c | 98 -- fs/fscache/internal.h | 317 +--- fs/fscache/io.c | 376 ++++- fs/fscache/main.c | 147 +- fs/fscache/netfs.c | 74 - fs/fscache/object.c | 1125 ------------- fs/fscache/operation.c | 633 ------- fs/fscache/page.c | 1242 -------------- fs/fscache/proc.c | 47 +- fs/fscache/stats.c | 293 +--- fs/fscache/volume.c | 517 ++++++ fs/namei.c | 3 +- fs/netfs/read_helper.c | 10 +- fs/nfs/Kconfig | 2 +- fs/nfs/Makefile | 2 +- fs/nfs/client.c | 4 - fs/nfs/direct.c | 2 + fs/nfs/file.c | 13 +- fs/nfs/fscache-index.c | 140 -- fs/nfs/fscache.c | 490 ++---- fs/nfs/fscache.h | 180 +- fs/nfs/inode.c | 11 +- fs/nfs/nfstrace.h | 1 - fs/nfs/read.c | 25 +- fs/nfs/super.c | 28 +- fs/nfs/write.c | 8 +- include/linux/fs.h | 4 + include/linux/fscache-cache.h | 614 ++----- include/linux/fscache.h | 1021 +++++------- include/linux/netfs.h | 15 +- include/linux/nfs_fs.h | 1 - include/linux/nfs_fs_sb.h | 9 +- include/linux/writeback.h | 1 + include/trace/events/cachefiles.h | 527 ++++-- include/trace/events/fscache.h | 642 ++++---- include/trace/events/netfs.h | 5 +- 105 files changed, 7396 insertions(+), 13509 deletions(-) delete mode 100644 Documentation/filesystems/caching/object.rst delete mode 100644 Documentation/filesystems/caching/operations.rst delete mode 100644 fs/afs/cache.c delete mode 100644 fs/cachefiles/bind.c create mode 100644 fs/cachefiles/cache.c create mode 100644 fs/cachefiles/error_inject.c delete mode 100644 fs/cachefiles/rdwr.c create mode 100644 fs/cachefiles/volume.c delete mode 100644 fs/cifs/cache.c delete mode 100644 fs/fscache/fsdef.c delete mode 100644 fs/fscache/netfs.c delete mode 100644 fs/fscache/object.c delete mode 100644 fs/fscache/operation.c delete mode 100644 fs/fscache/page.c create mode 100644 fs/fscache/volume.c delete mode 100644 fs/nfs/fscache-index.c