linux/mm/filemap.c, branch v5.0

mm/: remove caller signal_pending branch predictions

2019-01-04T21:13:48Z

This is already done for us internally by the signal machinery. Link: http://lkml.kernel.org/r/20181116002713.8474-5-dave@stgolabs.net Signed-off-by: Davidlohr Bueso Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, fault_around: do not take a reference to a locked page

2018-12-28T20:11:51Z

filemap_map_pages takes a speculative reference to each page in the range before it tries to lock that page. While this is correct it also can influence page migration which will bail out when seeing an elevated reference count. The faultaround code would bail on seeing a locked page so we can pro-actively check the PageLocked bit before page_cache_get_speculative and prevent from pointless reference count churn. Link: http://lkml.kernel.org/r/20181211142741.2607-4-mhocko@kernel.org Signed-off-by: Michal Hocko Suggested-by: Jan Kara Acked-by: Kirill A. Shutemov Reviewed-by: David Hildenbrand Acked-by: Hugh Dickins Reviewed-by: William Kucharski Cc: Oscar Salvador Cc: Pavel Tatashin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/filemap.c: remove useless check in pagecache_get_page()

2018-12-28T20:11:50Z

page always is not NULL, so we may remove this useless check. Link: http://lkml.kernel.org/r/154419752044.18559.2452963074922917720.stgit@localhost.localdomain Signed-off-by: Kirill Tkhai Acked-by: Cyrill Gorcunov Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: put_and_wait_on_page_locked() while page is migrated

2018-12-28T20:11:48Z

Waiting on a page migration entry has used wait_on_page_locked() all along since 2006: but you cannot safely wait_on_page_locked() without holding a reference to the page, and that extra reference is enough to make migrate_page_move_mapping() fail with -EAGAIN, when a racing task faults on the entry before migrate_page_move_mapping() gets there. And that failure is retried nine times, amplifying the pain when trying to migrate a popular page. With a single persistent faulter, migration sometimes succeeds; with two or three concurrent faulters, success becomes much less likely (and the more the page was mapped, the worse the overhead of unmapping and remapping it on each try). This is especially a problem for memory offlining, where the outer level retries forever (or until terminated from userspace), because a heavy refault workload can trigger an endless loop of migration failures. wait_on_page_locked() is the wrong tool for the job. David Herrmann (but was he the first?) noticed this issue in 2014: https://marc.info/?l=linux-mm&m=140110465608116&w=2 Tim Chen started a thread in August 2017 which appears relevant: https://marc.info/?l=linux-mm&m=150275941014915&w=2 where Kan Liang went on to implicate __migration_entry_wait(): https://marc.info/?l=linux-mm&m=150300268411980&w=2 and the thread ended up with the v4.14 commits: 2554db916586 ("sched/wait: Break up long wake list walk") 11a19c7b099f ("sched/wait: Introduce wakeup boomark in wake_up_page_bit") Baoquan He reported "Memory hotplug softlock issue" 14 November 2018: https://marc.info/?l=linux-mm&m=154217936431300&w=2 We have all assumed that it is essential to hold a page reference while waiting on a page lock: partly to guarantee that there is still a struct page when MEMORY_HOTREMOVE is configured, but also to protect against reuse of the struct page going to someone who then holds the page locked indefinitely, when the waiter can reasonably expect timely unlocking. But in fact, so long as wait_on_page_bit_common() does the put_page(), and is careful not to rely on struct page contents thereafter, there is no need to hold a reference to the page while waiting on it. That does mean that this case cannot go back through the loop: but that's fine for the page migration case, and even if used more widely, is limited by the "Stop walking if it's locked" optimization in wake_page_function(). Add interface put_and_wait_on_page_locked() to do this, using "behavior" enum in place of "lock" arg to wait_on_page_bit_common() to implement it. No interruptible or killable variant needed yet, but they might follow: I have a vague notion that reporting -EINTR should take precedence over return from wait_on_page_bit_common() without knowing the page state, so arrange it accordingly - but that may be nothing but pedantic. __migration_entry_wait() still has to take a brief reference to the page, prior to calling put_and_wait_on_page_locked(): but now that it is dropped before waiting, the chance of impeding page migration is very much reduced. Should we perhaps disable preemption across this? shrink_page_list()'s __ClearPageLocked(): that was a surprise! This survived a lot of testing before that showed up. PageWaiters may have been set by wait_on_page_bit_common(), and the reference dropped, just before shrink_page_list() succeeds in freezing its last page reference: in such a case, unlock_page() must be used. Follow the suggestion from Michal Hocko, just revert a978d6f52106 ("mm: unlockless reclaim") now: that optimization predates PageWaiters, and won't buy much these days; but we can reinstate it for the !PageWaiters case if anyone notices. It does raise the question: should vmscan.c's is_page_cache_freeable() and __remove_mapping() now treat a PageWaiters page as if an extra reference were held? Perhaps, but I don't think it matters much, since shrink_page_list() already had to win its trylock_page(), so waiters are not very common there: I noticed no difference when trying the bigger change, and it's surely not needed while put_and_wait_on_page_locked() is only used for page migration. [willy@infradead.org: add put_and_wait_on_page_locked() kerneldoc] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261121330.1116@eggly.anvils Signed-off-by: Hugh Dickins Reported-by: Baoquan He Tested-by: Baoquan He Reviewed-by: Andrea Arcangeli Acked-by: Michal Hocko Acked-by: Linus Torvalds Acked-by: Vlastimil Babka Cc: Matthew Wilcox Cc: Baoquan He Cc: David Hildenbrand Cc: Mel Gorman Cc: David Herrmann Cc: Tim Chen Cc: Kan Liang Cc: Andi Kleen Cc: Davidlohr Bueso Cc: Peter Zijlstra Cc: Christoph Lameter Cc: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'xfs-4.20-merge-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux

2018-11-02T16:33:08Z

Pull vfs dedup fixes from Dave Chinner: "This reworks the vfs data cloning infrastructure. We discovered many issues with these interfaces late in the 4.19 cycle - the worst of them (data corruption, setuid stripping) were fixed for XFS in 4.19-rc8, but a larger rework of the infrastructure fixing all the problems was needed. That rework is the contents of this pull request. Rework the vfs_clone_file_range and vfs_dedupe_file_range infrastructure to use a common .remap_file_range method and supply generic bounds and sanity checking functions that are shared with the data write path. The current VFS infrastructure has problems with rlimit, LFS file sizes, file time stamps, maximum filesystem file sizes, stripping setuid bits, etc and so they are addressed in these commits. We also introduce the ability for the ->remap_file_range methods to return short clones so that clones for vfs_copy_file_range() don't get rejected if the entire range can't be cloned. It also allows filesystems to sliently skip deduplication of partial EOF blocks if they are not capable of doing so without requiring errors to be thrown to userspace. Existing filesystems are converted to user the new remap_file_range method, and both XFS and ocfs2 are modified to make use of the new generic checking infrastructure" * tag 'xfs-4.20-merge-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux: (28 commits) xfs: remove [cm]time update from reflink calls xfs: remove xfs_reflink_remap_range xfs: remove redundant remap partial EOF block checks xfs: support returning partial reflink results xfs: clean up xfs_reflink_remap_blocks call site xfs: fix pagecache truncation prior to reflink ocfs2: remove ocfs2_reflink_remap_range ocfs2: support partial clone range and dedupe range ocfs2: fix pagecache truncation prior to reflink ocfs2: truncate page cache for clone destination file before remapping vfs: clean up generic_remap_file_range_prep return value vfs: hide file range comparison function vfs: enable remap callers that can handle short operations vfs: plumb remap flags through the vfs dedupe functions vfs: plumb remap flags through the vfs clone functions vfs: make remap_file_range functions take and return bytes completed vfs: remap helper should update destination inode metadata vfs: pass remap flags to generic_remap_checks vfs: pass remap flags to generic_remap_file_range_prep vfs: combine the clone and dedupe into a single remap_file_range ...

Merge branch 'work.afs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2018-11-02T02:58:52Z

Pull AFS updates from Al Viro: "AFS series, with some iov_iter bits included" * 'work.afs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (26 commits) missing bits of "iov_iter: Separate type from direction and use accessor functions" afs: Probe multiple fileservers simultaneously afs: Fix callback handling afs: Eliminate the address pointer from the address list cursor afs: Allow dumping of server cursor on operation failure afs: Implement YFS support in the fs client afs: Expand data structure fields to support YFS afs: Get the target vnode in afs_rmdir() and get a callback on it afs: Calc callback expiry in op reply delivery afs: Fix FS.FetchStatus delivery from updating wrong vnode afs: Implement the YFS cache manager service afs: Remove callback details from afs_callback_break struct afs: Commit the status on a new file/dir/symlink afs: Increase to 64-bit volume ID and 96-bit vnode ID for YFS afs: Don't invoke the server to read data beyond EOF afs: Add a couple of tracepoints to log I/O errors afs: Handle EIO from delivery function afs: Fix TTL on VL server and address lists afs: Implement VL server rotation afs: Improve FS server rotation error handling ...

vfs: enable remap callers that can handle short operations

2018-10-29T23:42:10Z

Plumb in a remap flag that enables the filesystem remap handler to shorten remapping requests for callers that can handle it. Now copy_file_range can report partial success (in case we run up against alignment problems, resource limits, etc.). We also enable CAN_SHORTEN for fideduperange to maintain existing userspace-visible behavior where xfs/btrfs shorten the dedupe range to avoid stale post-eof data exposure. Signed-off-by: Darrick J. Wong Reviewed-by: Amir Goldstein Signed-off-by: Dave Chinner

vfs: make remap_file_range functions take and return bytes completed

2018-10-29T23:41:49Z

Change the remap_file_range functions to take a number of bytes to operate upon and return the number of bytes they operated on. This is a requirement for allowing fs implementations to return short clone/dedupe results to the user, which will enable us to obey resource limits in a graceful manner. A subsequent patch will enable copy_file_range to signal to the ->clone_file_range implementation that it can handle a short length, which will be returned in the function's return value. For now the short return is not implemented anywhere so the behavior won't change -- either copy_file_range manages to clone the entire range or it tries an alternative. Neither clone ioctl can take advantage of this, alas. Signed-off-by: Darrick J. Wong Reviewed-by: Amir Goldstein Signed-off-by: Dave Chinner

vfs: pass remap flags to generic_remap_checks

2018-10-29T23:41:34Z

Pass the same remap flags to generic_remap_checks for consistency. Signed-off-by: Darrick J. Wong Reviewed-by: Amir Goldstein Reviewed-by: Christoph Hellwig Signed-off-by: Dave Chinner

vfs: strengthen checking of file range inputs to generic_remap_checks

2018-10-29T23:40:46Z

File range remapping, if allowed to run past the destination file's EOF, is an optimization on a regular file write. Regular file writes that extend the file length are subject to various constraints which are not checked by range cloning. This is a correctness problem because we're never allowed to touch ranges that the page cache can't support (s_maxbytes); we're not supposed to deal with large offsets (MAX_NON_LFS) if O_LARGEFILE isn't set; and we must obey resource limits (RLIMIT_FSIZE). Therefore, add these checks to the new generic_remap_checks function so that we curtail unexpected behavior. Signed-off-by: Darrick J. Wong Reviewed-by: Amir Goldstein Reviewed-by: Christoph Hellwig Signed-off-by: Dave Chinner