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  1. 21 10月, 2019 6 次提交
  3. 01 7月, 2019 5 次提交
  5. 29 6月, 2019 3 次提交
  7. 17 6月, 2019 1 次提交
  9. 30 4月, 2019 1 次提交
  11. 17 4月, 2019 2 次提交
    • D
      xfs: merge adjacent io completions of the same type · 3994fc48
      由 Darrick J. Wong 提交于 
      It's possible for pagecache writeback to split up a large amount of work
into smaller pieces for throttling purposes or to reduce the amount of
time a writeback operation is pending.  Whatever the reason, XFS can end
up with a bunch of IO completions that call for the same operation to be
performed on a contiguous extent mapping.  Since mappings are extent
based in XFS, we'd prefer to run fewer transactions when we can.

When we're processing an ioend on the list of io completions, check to
see if the next items on the list are both adjacent and of the same
type.  If so, we can merge the completions to reduce transaction
overhead.

On fast storage this doesn't seem to make much of a difference in
performance, though the number of transactions for an overnight xfstests
run seems to drop by ~5%.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
      3994fc48
    • D
      xfs: implement per-inode writeback completion queues · cb357bf3
      由 Darrick J. Wong 提交于 
      When scheduling writeback of dirty file data in the page cache, XFS uses
IO completion workqueue items to ensure that filesystem metadata only
updates after the write completes successfully.  This is essential for
converting unwritten extents to real extents at the right time and
performing COW remappings.

Unfortunately, XFS queues each IO completion work item to an unbounded
workqueue, which means that the kernel can spawn dozens of threads to
try to handle the items quickly.  These threads need to take the ILOCK
to update file metadata, which results in heavy ILOCK contention if a
large number of the work items target a single file, which is
inefficient.

Worse yet, the writeback completion threads get stuck waiting for the
ILOCK while holding transaction reservations, which can use up all
available log reservation space.  When that happens, metadata updates to
other parts of the filesystem grind to a halt, even if the filesystem
could otherwise have handled it.

Even worse, if one of the things grinding to a halt happens to be a
thread in the middle of a defer-ops finish holding the same ILOCK and
trying to obtain more log reservation having exhausted the permanent
reservation, we now have an ABBA deadlock - writeback completion has a
transaction reserved and wants the ILOCK, and someone else has the ILOCK
and wants a transaction reservation.

Therefore, we create a per-inode writeback io completion queue + work
item.  When writeback finishes, it can add the ioend to the per-inode
queue and let the single worker item process that queue.  This
dramatically cuts down on the number of kworkers and ILOCK contention in
the system, and seems to have eliminated an occasional deadlock I was
seeing while running generic/476.

Testing with a program that simulates a heavy random-write workload to a
single file demonstrates that the number of kworkers drops from
approximately 120 threads per file to 1, without dramatically changing
write bandwidth or pagecache access latency.

Note that we leave the xfs-conv workqueue's max_active alone because we
still want to be able to run ioend processing for as many inodes as the
system can handle.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
      cb357bf3
  13. 21 2月, 2019 2 次提交
    • C
      xfs: introduce an always_cow mode · 66ae56a5
      由 Christoph Hellwig 提交于 
      Add a mode where XFS never overwrites existing blocks in place.  This
is to aid debugging our COW code, and also put infatructure in place
for things like possible future support for zoned block devices, which
can't support overwrites.

This mode is enabled globally by doing a:

    echo 1 > /sys/fs/xfs/debug/always_cow

Note that the parameter is global to allow running all tests in xfstests
easily in this mode, which would not easily be possible with a per-fs
sysfs file.

In always_cow mode persistent preallocations are disabled, and fallocate
will fail when called with a 0 mode (with our without
FALLOC_FL_KEEP_SIZE), and not create unwritten extent for zeroed space
when called with FALLOC_FL_ZERO_RANGE or FALLOC_FL_UNSHARE_RANGE.

There are a few interesting xfstests failures when run in always_cow
mode:

 - generic/392 fails because the bytes used in the file used to test
   hole punch recovery are less after the log replay.  This is
   because the blocks written and then punched out are only freed
   with a delay due to the logging mechanism.
 - xfs/170 will fail as the already fragile file streams mechanism
   doesn't seem to interact well with the COW allocator
 - xfs/180 xfs/182 xfs/192 xfs/198 xfs/204 and xfs/208 will claim
   the file system is badly fragmented, but there is not much we
   can do to avoid that when always writing out of place
 - xfs/205 fails because overwriting a file in always_cow mode
   will require new space allocation and the assumption in the
   test thus don't work anymore.
 - xfs/326 fails to modify the file at all in always_cow mode after
   injecting the refcount error, leading to an unexpected md5sum
   after the remount, but that again is expected
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
      66ae56a5
    • C
      xfs: also truncate holes covered by COW blocks · 12df89f2
      由 Christoph Hellwig 提交于 
      This only matters if we want to write data through the COW fork that is
not actually an overwrite of existing data.  Reasons for that are
speculative COW fork allocations using the cowextsize, or a mode where
we always write through the COW fork.  Currently both can't actually
happen, but I plan to enable them.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
      12df89f2
  15. 18 2月, 2019 5 次提交
  17. 15 2月, 2019 2 次提交
  19. 12 2月, 2019 2 次提交
    • B
      xfs: remove superfluous writeback mapping eof trimming · 3b350898
      由 Brian Foster 提交于 
      Now that the cached writeback mapping is explicitly invalidated on
data fork changes, the EOF trimming band-aid is no longer necessary.
Remove xfs_trim_extent_eof() as well since it has no other users.
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
      3b350898
    • B
      xfs: validate writeback mapping using data fork seq counter · d9252d52
      由 Brian Foster 提交于 
      The writeback code caches the current extent mapping across multiple
xfs_do_writepage() calls to avoid repeated lookups for sequential
pages backed by the same extent. This is known to be slightly racy
with extent fork changes in certain difficult to reproduce
scenarios. The cached extent is trimmed to within EOF to help avoid
the most common vector for this problem via speculative
preallocation management, but this is a band-aid that does not
address the fundamental problem.

Now that we have an xfs_ifork sequence counter mechanism used to
facilitate COW writeback, we can use the same mechanism to validate
consistency between the data fork and cached writeback mappings. On
its face, this is somewhat of a big hammer approach because any
change to the data fork invalidates any mapping currently cached by
a writeback in progress regardless of whether the data fork change
overlaps with the range under writeback. In practice, however, the
impact of this approach is minimal in most cases.

First, data fork changes (delayed allocations) caused by sustained
sequential buffered writes are amortized across speculative
preallocations. This means that a cached mapping won't be
invalidated by each buffered write of a common file copy workload,
but rather only on less frequent allocation events. Second, the
extent tree is always entirely in-core so an additional lookup of a
usable extent mostly costs a shared ilock cycle and in-memory tree
lookup. This means that a cached mapping reval is relatively cheap
compared to the I/O itself. Third, spurious invalidations don't
impact ioend construction. This means that even if the same extent
is revalidated multiple times across multiple writepage instances,
we still construct and submit the same size ioend (and bio) if the
blocks are physically contiguous.

Update struct xfs_writepage_ctx with a new field to hold the
sequence number of the data fork associated with the currently
cached mapping. Check the wpc seqno against the data fork when the
mapping is validated and reestablish the mapping whenever the fork
has changed since the mapping was cached. This ensures that
writeback always uses a valid extent mapping and thus prevents lost
writebacks and stale delalloc block problems.
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NAllison Henderson <allison.henderson@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
      d9252d52
  21. 04 2月, 2019 1 次提交
    • B
      xfs: eof trim writeback mapping as soon as it is cached · aa6ee4ab
      由 Brian Foster 提交于 
      The cached writeback mapping is EOF trimmed to try and avoid races
between post-eof block management and writeback that result in
sending cached data to a stale location. The cached mapping is
currently trimmed on the validation check, which leaves a race
window between the time the mapping is cached and when it is trimmed
against the current inode size.

For example, if a new mapping is cached by delalloc conversion on a
blocksize == page size fs, we could cycle various locks, perform
memory allocations, etc.  in the writeback codepath before the
associated mapping is eventually trimmed to i_size. This leaves
enough time for a post-eof truncate and file append before the
cached mapping is trimmed. The former event essentially invalidates
a range of the cached mapping and the latter bumps the inode size
such the trim on the next writepage event won't trim all of the
invalid blocks. fstest generic/464 reproduces this scenario
occasionally and causes a lost writeback and stale delalloc blocks
warning on inode inactivation.

To work around this problem, trim the cached writeback mapping as
soon as it is cached in addition to on subsequent validation checks.
This is a minor tweak to tighten the race window as much as possible
until a proper invalidation mechanism is available.

Fixes: 40214d12 ("xfs: trim writepage mapping to within eof")
Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NAllison Henderson <allison.henderson@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
      aa6ee4ab
  23. 18 10月, 2018 1 次提交
  25. 08 8月, 2018 1 次提交
  27. 01 8月, 2018 1 次提交
  29. 30 7月, 2018 1 次提交
  31. 12 7月, 2018 6 次提交