| Message ID | 20240429190500.30979-1-ryncsn@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | mm/swap: clean up and optimize swap cache index | expand |
Kairui Song <ryncsn@gmail.com> writes: > From: Kairui Song <kasong@tencent.com> > > This is based on latest mm-unstable. Patch 1/12 might not be needed if > f2fs converted .readahead to use folio, I included it for easier test > and review. > > Currently we use one swap_address_space for every 64M chunk to reduce lock > contention, this is like having a set of smaller swap files inside one > big swap file. I would rather to say, " this is like having a set of smaller files inside a swap device. " To avoid possible confusing in this series. I suggest to avoid to say "swap file". Instead, we can use "swap device". [snip] -- Best Regards, Huang, Ying
On Tue, Apr 30, 2024 at 10:47 AM Huang, Ying <ying.huang@intel.com> wrote: > > Kairui Song <ryncsn@gmail.com> writes: > > > From: Kairui Song <kasong@tencent.com> > > > > This is based on latest mm-unstable. Patch 1/12 might not be needed if > > f2fs converted .readahead to use folio, I included it for easier test > > and review. > > > > Currently we use one swap_address_space for every 64M chunk to reduce lock > > contention, this is like having a set of smaller swap files inside one > > big swap file. > > I would rather to say, > > " > this is like having a set of smaller files inside a swap device. > " > > To avoid possible confusing in this series. I suggest to avoid to say > "swap file". Instead, we can use "swap device". Good suggestion, will update this part. > [snip] > > -- > Best Regards, > Huang, Ying
From: Kairui Song <kasong@tencent.com> This is based on latest mm-unstable. Patch 1/12 might not be needed if f2fs converted .readahead to use folio, I included it for easier test and review. Currently we use one swap_address_space for every 64M chunk to reduce lock contention, this is like having a set of smaller swap files inside one big swap file. But when doing swap cache look up or insert, we are still using the offset of the whole large swap file. This is OK for correctness, as the offset (key) is unique. But Xarray is specially optimized for small indexes, it creates the redix tree levels lazily to be just enough to fit the largest key stored in one Xarray. So we are wasting tree nodes unnecessarily. For 64M chunk it should only take at most 3 level to contain everything. But we are using the offset from the whole swap file, so the offset (key) value will be way beyond 64M, and so will the tree level. Optimize this by reduce the swap cache search space into 64M scope. Test with `time memhog 128G` inside a 8G memcg using 128G swap (ramdisk with SWP_SYNCHRONOUS_IO dropped, tested 3 times, results are stable. The test result is similar but the improvement is smaller if SWP_SYNCHRONOUS_IO is enabled, as swap out path can never skip swap cache): Before: 6.07user 250.74system 4:17.26elapsed 99%CPU (0avgtext+0avgdata 8373376maxresident)k 0inputs+0outputs (55major+33555018minor)pagefaults 0swaps After (+1.8% faster): 6.08user 246.09system 4:12.58elapsed 99%CPU (0avgtext+0avgdata 8373248maxresident)k 0inputs+0outputs (54major+33555027minor)pagefaults 0swaps Similar result with MySQL and sysbench using swap: Before: 94055.61 qps After (+0.8% faster): 94834.91 qps There is alse a very slight drop of radix tree node slab usage: Before: 303952K After: 302224K For this series: There are multiple places that expect mixed type of pages (page cache or swap cache), eg. migration, huge memory split; There are four helpers for that: - page_index - page_file_offset - folio_index - folio_file_pos To keep the code clean and compatible, this series first cleaned up usage of them. First page_file_offset and folio_file_pos are historical helpes that can be simply dropped after clean up. And page_index can be all converted to folio_index or folio->index. Then introduce two new helpers swap_cache_index and swap_dev_pos for swap. Replace swp_offset with swap_cache_index when used to retrieve folio from swap cache, and use swap_dev_pos when needed to retrieve the device position of a swap entry. This way, swap_cache_index can return the optimized value with no compatibility issue. Idealy, in the future, we may want to reduce SWAP_ADDRESS_SPACE_SHIFT from 14 to 12: Default Xarray chunk offset is 6, so we have 3 level trees instead of 2 level trees just for 2 extra bits. But swap cache is based on address_space struct, with 4 times more metadata sparsely distributed in memory it waste more cacheline, the performance gain from this series is almost canceled according to my test. So first, just have a cleaner seperation of offsets and smaller search space. Patch 1/12 - 11/12: Clean up usage of above helpers. Patch 11/12: Apply the optmization. V2: https://lore.kernel.org/linux-mm/20240423170339.54131-1-ryncsn@gmail.com/ Update from V2: - Clean up usage of page_file_offset and folio_file_pos [Matthew Wilcox] https://lore.kernel.org/linux-mm/ZiiFHTwgu8FGio1k@casper.infradead.org/ - Use folio in nilfs_bmap_data_get_key [Ryusuke Konishi] V1: https://lore.kernel.org/all/20240417160842.76665-1-ryncsn@gmail.com/ Update from V1: - Convert more users to use folio directly when possible [Matthew Wilcox] - Rename swap_file_pos to swap_dev_pos [Huang, Ying] - Update comments and commit message. - Adjust headers and add dummy function to fix build error. This series is part of effort to reduce swap cache overhead, and ultimately remove SWP_SYNCHRONOUS_IO and unify swap cache usage as proposed before: https://lore.kernel.org/lkml/20240326185032.72159-1-ryncsn@gmail.com/ Kairui Song (12): f2fs: drop usage of page_index nilfs2: drop usage of page_index ceph: drop usage of page_index NFS: remove nfs_page_lengthg and usage of page_index cifs: drop usage of page_file_offset afs: drop usage of folio_file_pos netfs: drop usage of folio_file_pos nfs: drop usage of folio_file_pos mm/swap: get the swap file offset directly mm: remove page_file_offset and folio_file_pos mm: drop page_index and convert folio_index to use folio mm/swap: reduce swap cache search space fs/afs/dir.c | 6 +++--- fs/afs/dir_edit.c | 4 ++-- fs/ceph/dir.c | 2 +- fs/ceph/inode.c | 2 +- fs/f2fs/data.c | 2 +- fs/netfs/buffered_read.c | 4 ++-- fs/netfs/buffered_write.c | 2 +- fs/nfs/file.c | 2 +- fs/nfs/internal.h | 19 ------------------- fs/nfs/nfstrace.h | 4 ++-- fs/nfs/write.c | 6 +++--- fs/nilfs2/bmap.c | 3 +-- fs/smb/client/file.c | 2 +- include/linux/mm.h | 13 ------------- include/linux/pagemap.h | 25 ++++--------------------- mm/huge_memory.c | 2 +- mm/memcontrol.c | 2 +- mm/mincore.c | 2 +- mm/page_io.c | 6 +++--- mm/shmem.c | 2 +- mm/swap.h | 24 ++++++++++++++++++++++++ mm/swap_state.c | 12 ++++++------ mm/swapfile.c | 11 +++++------ 23 files changed, 65 insertions(+), 92 deletions(-)