| Message ID | 2506007.1711562145@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC,v2] mm, netfs: Provide a means of invalidation without using launder_folio | expand |
On Wed, Mar 27, 2024 at 05:55:45PM +0000, David Howells wrote: > +int filemap_invalidate_inode(struct inode *inode, bool flush) > +{ > + struct address_space *mapping = inode->i_mapping; > + > + if (!mapping || !mapping->nrpages) > + goto out; > + > + /* Prevent new folios from being added to the inode. */ > + filemap_invalidate_lock(mapping); I'm kind of surprised that the callers wouldn't want to hold that lock over a call to this function. I guess you're working on the callers, so you'd know better than I would, but I would have used lockdep to assert that invalidate_lock was held. > + if (!mapping->nrpages) > + goto unlock; > + > + /* Assume there are probably PTEs only if there are mmaps. */ > + if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))) > + unmap_mapping_pages(mapping, 0, ULONG_MAX, false); Is this optimisation worth it? We're already doing some expensive operations here, does saving cycling the i_mmap_lock really help anything? You'll note that unmap_mapping_pages() already does this check inside the lock.
Matthew Wilcox <willy@infradead.org> wrote: > > + /* Prevent new folios from being added to the inode. */ > > + filemap_invalidate_lock(mapping); > > I'm kind of surprised that the callers wouldn't want to hold that lock > over a call to this function. I guess you're working on the callers, > so you'd know better than I would, but I would have used lockdep to > assert that invalidate_lock was held. I'm not sure. None of the places that look like they'd be calling this currently take that lock (though possibly they should). Also, should I provide it with explicit range, I wonder? > > + if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))) > > + unmap_mapping_pages(mapping, 0, ULONG_MAX, false); > > Is this optimisation worth it? Perhaps not. David
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 2df35e65557d..4eb3d4177a53 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -40,6 +40,7 @@ int filemap_fdatawait_keep_errors(struct address_space *mapping); int filemap_fdatawait_range(struct address_space *, loff_t lstart, loff_t lend); int filemap_fdatawait_range_keep_errors(struct address_space *mapping, loff_t start_byte, loff_t end_byte); +int filemap_invalidate_inode(struct inode *inode, bool flush); static inline int filemap_fdatawait(struct address_space *mapping) { diff --git a/mm/filemap.c b/mm/filemap.c index 25983f0f96e3..98f439bedb44 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -4134,6 +4134,54 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp) } EXPORT_SYMBOL(filemap_release_folio); +/** + * filemap_invalidate_inode - Invalidate/forcibly write back an inode's pagecache + * @inode: The inode to flush + * @flush: Set to write back rather than simply invalidate. + * + * Invalidate all the folios on an inode, possibly writing them back first. + * Whilst the operation is undertaken, the invalidate lock is held to prevent + * new folios from being installed. + */ +int filemap_invalidate_inode(struct inode *inode, bool flush) +{ + struct address_space *mapping = inode->i_mapping; + + if (!mapping || !mapping->nrpages) + goto out; + + /* Prevent new folios from being added to the inode. */ + filemap_invalidate_lock(mapping); + + if (!mapping->nrpages) + goto unlock; + + /* Assume there are probably PTEs only if there are mmaps. */ + if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))) + unmap_mapping_pages(mapping, 0, ULONG_MAX, false); + + /* Write back the data if we're asked to. */ + if (flush) { + struct writeback_control wbc = { + .sync_mode = WB_SYNC_ALL, + .nr_to_write = LONG_MAX, + .range_start = 0, + .range_end = LLONG_MAX, + }; + + filemap_fdatawrite_wbc(mapping, &wbc); + } + + /* Wait for writeback to complete on all folios and discard. */ + truncate_inode_pages_range(mapping, 0, LLONG_MAX); + +unlock: + filemap_invalidate_unlock(mapping); +out: + return filemap_check_errors(mapping); +} +EXPORT_SYMBOL(filemap_invalidate_inode); + #ifdef CONFIG_CACHESTAT_SYSCALL /** * filemap_cachestat() - compute the page cache statistics of a mapping
mm, netfs: Provide a means of invalidation without using launder_folio Implement a replacement for launder_folio. The key feature of invalidate_inode_pages2() is that it locks each folio individually, unmaps it to prevent mmap'd accesses interfering and calls the ->launder_folio() address_space op to flush it. This has problems: firstly, each folio is written individually as one or more small writes; secondly, adjacent folios cannot be added so easily into the laundry; thirdly, it's yet another op to implement. Instead, use the invalidate lock to cause anyone wanting to add a folio to the inode to wait, then unmap all the folios if we have mmaps, then, conditionally, use ->writepages() to flush any dirty data back and then discard all pages. The invalidate lock prevents ->read_iter(), ->write_iter() and faulting through mmap all from adding pages for the duration. Signed-off-by: David Howells <dhowells@redhat.com> cc: Matthew Wilcox <willy@infradead.org> cc: Miklos Szeredi <miklos@szeredi.hu> cc: Trond Myklebust <trond.myklebust@hammerspace.com> cc: Christoph Hellwig <hch@lst.de> cc: Andrew Morton <akpm@linux-foundation.org> cc: Alexander Viro <viro@zeniv.linux.org.uk> cc: Christian Brauner <brauner@kernel.org> cc: Jeff Layton <jlayton@kernel.org> cc: linux-mm@kvack.org cc: linux-fsdevel@vger.kernel.org cc: netfs@lists.linux.dev cc: v9fs@lists.linux.dev cc: linux-afs@lists.infradead.org cc: ceph-devel@vger.kernel.org cc: linux-cifs@vger.kernel.org cc: linux-nfs@vger.kernel.org cc: devel@lists.orangefs.org --- include/linux/pagemap.h | 1 + mm/filemap.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 49 insertions(+)