linux-stable.git/fs/fs-writeback.c, branch v5.18.2

writeback: Avoid skipping inode writeback

2022-05-10T10:04:21+00:00

We have run into an issue that a task gets stuck in
balance_dirty_pages_ratelimited() when perform I/O stress testing.
The reason we observed is that an I_DIRTY_PAGES inode with lots
of dirty pages is in b_dirty_time list and standard background
writeback cannot writeback the inode.
After studing the relevant code, the following scenario may lead
to the issue:

task1                                   task2
-----                                   -----
fuse_flush
 write_inode_now //in b_dirty_time
  writeback_single_inode
   __writeback_single_inode
                                 fuse_write_end
                                  filemap_dirty_folio
                                   __xa_set_mark:PAGECACHE_TAG_DIRTY
    lock inode->i_lock
    if mapping tagged PAGECACHE_TAG_DIRTY
    inode->i_state |= I_DIRTY_PAGES
    unlock inode->i_lock
                                   __mark_inode_dirty:I_DIRTY_PAGES
                                      lock inode->i_lock
                                      -was dirty,inode stays in
                                      -b_dirty_time
                                      unlock inode->i_lock

   if(!(inode->i_state & I_DIRTY_All))
      -not true,so nothing done

This patch moves the dirty inode to b_dirty list when the inode
currently is not queued in b_io or b_more_io list at the end of
writeback_single_inode.

Reviewed-by: Jan Kara 
Reviewed-by: Christoph Hellwig 
CC: stable@vger.kernel.org
Fixes: 0ae45f63d4ef ("vfs: add support for a lazytime mount option")
Signed-off-by: Jing Xia 
Signed-off-by: Jan Kara 
Link: https://lore.kernel.org/r/20220510023514.27399-1-jing.xia@unisoc.com

Merge branch 'akpm' (patches from Andrew)

2022-03-22T23:11:53+00:00

Merge updates from Andrew Morton:

 - A few misc subsystems: kthread, scripts, ntfs, ocfs2, block, and vfs

 - Most the MM patches which precede the patches in Willy's tree: kasan,
   pagecache, gup, swap, shmem, memcg, selftests, pagemap, mremap,
   sparsemem, vmalloc, pagealloc, memory-failure, mlock, hugetlb,
   userfaultfd, vmscan, compaction, mempolicy, oom-kill, migration, thp,
   cma, autonuma, psi, ksm, page-poison, madvise, memory-hotplug, rmap,
   zswap, uaccess, ioremap, highmem, cleanups, kfence, hmm, and damon.

* emailed patches from Andrew Morton : (227 commits)
  mm/damon/sysfs: remove repeat container_of() in damon_sysfs_kdamond_release()
  Docs/ABI/testing: add DAMON sysfs interface ABI document
  Docs/admin-guide/mm/damon/usage: document DAMON sysfs interface
  selftests/damon: add a test for DAMON sysfs interface
  mm/damon/sysfs: support DAMOS stats
  mm/damon/sysfs: support DAMOS watermarks
  mm/damon/sysfs: support schemes prioritization
  mm/damon/sysfs: support DAMOS quotas
  mm/damon/sysfs: support DAMON-based Operation Schemes
  mm/damon/sysfs: support the physical address space monitoring
  mm/damon/sysfs: link DAMON for virtual address spaces monitoring
  mm/damon: implement a minimal stub for sysfs-based DAMON interface
  mm/damon/core: add number of each enum type values
  mm/damon/core: allow non-exclusive DAMON start/stop
  Docs/damon: update outdated term 'regions update interval'
  Docs/vm/damon/design: update DAMON-Idle Page Tracking interference handling
  Docs/vm/damon: call low level monitoring primitives the operations
  mm/damon: remove unnecessary CONFIG_DAMON option
  mm/damon/paddr,vaddr: remove damon_{p,v}a_{target_valid,set_operations}()
  mm/damon/dbgfs-test: fix is_target_id() change
  ...

mm/fs: delete PF_SWAPWRITE

2022-03-22T22:57:08+00:00

PF_SWAPWRITE has been redundant since v3.2 commit ee72886d8ed5 ("mm:
vmscan: do not writeback filesystem pages in direct reclaim").

Coincidentally, NeilBrown's current patch "remove inode_congested()"
deletes may_write_to_inode(), which appeared to be the one function which
took notice of PF_SWAPWRITE.  But if you study the old logic, and the
conditions under which may_write_to_inode() was called, you discover that
flag and function have been pointless for a decade.

Link: https://lkml.kernel.org/r/75e80e7-742d-e3bd-531-614db8961e4@google.com
Signed-off-by: Hugh Dickins 
Cc: NeilBrown 
Cc: Jan Kara 
Cc: "Darrick J. Wong" 
Cc: Dave Chinner 
Cc: Matthew Wilcox 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

remove inode_congested()

2022-03-22T22:57:01+00:00

inode_congested() reports if the backing-device for the inode is
congested.  No bdi reports congestion any more, so this always returns
'false'.

So remove inode_congested() and related functions, and remove the call
sites, assuming that inode_congested() always returns 'false'.

Link: https://lkml.kernel.org/r/164549983741.9187.2174285592262191311.stgit@noble.brown
Signed-off-by: NeilBrown 
Cc: Anna Schumaker 
Cc: Chao Yu 
Cc: Darrick J. Wong 
Cc: Ilya Dryomov 
Cc: Jaegeuk Kim 
Cc: Jan Kara 
Cc: Jeff Layton 
Cc: Jens Axboe 
Cc: Lars Ellenberg 
Cc: Miklos Szeredi 
Cc: Paolo Valente 
Cc: Philipp Reisner 
Cc: Ryusuke Konishi 
Cc: Trond Myklebust 
Cc: Wu Fengguang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

block: check that there is a plug in blk_flush_plug

2022-02-02T14:50:00+00:00

Rename blk_flush_plug to __blk_flush_plug and add a wrapper that includes
the NULL check instead of open coding that check everywhere.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Chaitanya Kulkarni 
Link: https://lore.kernel.org/r/20220127070549.1377856-2-hch@lst.de
Signed-off-by: Jens Axboe

block: remove blk_needs_flush_plug

2022-02-02T14:50:00+00:00

blk_needs_flush_plug fails to account for the cb_list, which needs
flushing as well.  Remove it and just check if there is a plug instead
of poking into the internals of the plug structure.

Signed-off-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20220127070549.1377856-1-hch@lst.de
Signed-off-by: Jens Axboe

Merge tag 'fscache-rewrite-20220111' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

2022-01-12T21:45:12+00:00

Pull fscache rewrite from David Howells:
"This is a set of patches that rewrites the fscache driver and 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 series 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.

[!] Note: I have dropped the cifs patch for the moment, leaving local
caching in cifs disabled. I've been having trouble getting that
working. I think I have it done, but it needs more testing (there
seem to be some test failures occurring with v5.16 also from
xfstests), so I propose deferring that patch to the end of the
merge window.

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 with the dropped patch) 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"

Link: https://lore.kernel.org/all/510611.1641942444@warthog.procyon.org.uk/
Tested-by: Dominique Martinet # 9p
Tested-by: kafs-testing@auristor.com # afs
Tested-by: Jeff Layton # ceph
Tested-by: Dave Wysochanski # nfs
Tested-by: Daire Byrne # nfs

* tag 'fscache-rewrite-20220111' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs: (67 commits)
9p, afs, ceph, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking()
fscache: Add a tracepoint for cookie use/unuse
fscache: Rewrite documentation
ceph: add fscache writeback support
ceph: conversion to new fscache API
nfs: Implement cache I/O by accessing the cache directly
nfs: Convert to new fscache volume/cookie API
9p: Copy local writes to the cache when writing to the server
9p: Use fscache indexing rewrite and reenable caching
afs: Skip truncation on the server of data we haven't written yet
afs: Copy local writes to the cache when writing to the server
afs: Convert afs to use the new fscache API
fscache, cachefiles: Display stat of culling events
fscache, cachefiles: Display stats of no-space events
cachefiles: Allow cachefiles to actually function
fscache, cachefiles: Store the volume coherency data
cachefiles: Implement the I/O routines
cachefiles: Implement cookie resize for truncate
cachefiles: Implement begin and end I/O operation
cachefiles: Implement backing file wrangling
...

vfs, fscache: Implement pinning of cache usage for writeback

2022-01-07T09:22:19+00:00

Cachefiles has a problem in that it needs to keep the backing file for a
cookie open whilst there are local modifications pending that need to be
written to it.  However, we don't want to keep the file open indefinitely,
as that causes EMFILE/ENFILE/ENOMEM 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
other resources that have already been dismantled.

To get around this, I added the following:

 (1) 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.

 (2) 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.

 (3) 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.

 (4) A function, fscache_unpin_writeback(), to be called by ->write_inode()
     to unuse the cookie.

 (5) 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

Signed-off-by: David Howells 
Reviewed-by: Jeff Layton 
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819615157.215744.17623791756928043114.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906917856.143852.8224898306177154573.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967124567.1823006.14188359004568060298.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021524705.640689.17824932021727663017.stgit@warthog.procyon.org.uk/ # v4

fs/writeback: Convert inode_switch_wbs_work_fn to folios

2022-01-03T01:28:49+00:00

This gets the statistics correct for large folios by modifying the
counters by the number of pages in the folio instead of by 1.

Signed-off-by: Matthew Wilcox (Oracle) 
Reviewed-by: Christoph Hellwig 
Reviewed-by: William Kucharski

Merge tag 'kspp-misc-fixes-5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux

2021-11-02T00:29:10+00:00

Pull hardening fixes and cleanups from Gustavo A. R. Silva:
 "Various hardening fixes and cleanups that I've been collecting during
  the last development cycle:

  Fix -Wcast-function-type error:

   - firewire: Remove function callback casts (Oscar Carter)

  Fix application of sizeof operator:

   - firmware/psci: fix application of sizeof to pointer (jing yangyang)

  Replace open coded instances with size_t saturating arithmetic
  helpers:

   - assoc_array: Avoid open coded arithmetic in allocator arguments
     (Len Baker)

   - writeback: prefer struct_size over open coded arithmetic (Len
     Baker)

   - aio: Prefer struct_size over open coded arithmetic (Len Baker)

   - dmaengine: pxa_dma: Prefer struct_size over open coded arithmetic
     (Len Baker)

  Flexible array transformation:

   - KVM: PPC: Replace zero-length array with flexible array member (Len
     Baker)

  Use 2-factor argument multiplication form:

   - nouveau/svm: Use kvcalloc() instead of kvzalloc() (Gustavo A. R.
     Silva)

   - xfs: Use kvcalloc() instead of kvzalloc() (Gustavo A. R. Silva)"

* tag 'kspp-misc-fixes-5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux:
  firewire: Remove function callback casts
  nouveau/svm: Use kvcalloc() instead of kvzalloc()
  firmware/psci: fix application of sizeof to pointer
  dmaengine: pxa_dma: Prefer struct_size over open coded arithmetic
  KVM: PPC: Replace zero-length array with flexible array member
  aio: Prefer struct_size over open coded arithmetic
  writeback: prefer struct_size over open coded arithmetic
  xfs: Use kvcalloc() instead of kvzalloc()
  assoc_array: Avoid open coded arithmetic in allocator arguments