[00/10,v6] xfs: intent whiteouts

Message

Dave Chinner May 3, 2022, 10:17 p.m. UTC

This is a patchset inspired by the performance regressions that were
seen from logging 64k xattrs with Allison's delayed attribute
patchset and trying to work out how to minimise the impact of
logging xattrs. Most of that is explained in the "xfs: intent item
whiteouts" patch, so I won't repeat it here.

The whiteouts massively reduce the journal write overhead of logging
xattrs - with this patchset I've reduced 2.5GB/s of log traffic (16
way file create w/64k xattr workload) down to approximately 220MB of
log traffic, and performance has increased from 9k creates/s to 36k
creates/s. The workload still writes to disk at 2.5GB/s, but that's
what writing 35k x 64k xattrs to disk does.

This is still short of the non-logged attribute mechanism, which
runs at 40-45k creates a second and 3.5-4GB/s to disk, but it brings
logged attrs to within roughly 5-15% of non-logged attrs across the
full range of attribute sizes.

So, while this patchset was clearly insired and has major positive
impact on Allison's delayed attribute work, it also applies
generically to all other intent/intent done pairs that already
exist. Hence I've created this patchset as a stand-alone patchset
that isn't dependent on the delayed attributes being committed, nor
does the delayed attribute patchset need this to funciton properly.
IOWs, they can be merged in parallel and then the attribute log item
implementation be updated to support whiteouts after the fact.

This patchset is separate to the attr code, though, because
intent whiteouts are not specific to the attr code. They are a
generic mechanism that can be applied to all the intent/intent done
item pairs we already have. This patch set modifies all those
intents to use whiteouts, and so there is benefits from the patch
set for all operations that use these intents.

Changelog:

Version 6:
- added backportable bug fix for inode fork data leak to start of series
- added backportable bug fix for intent shadow buffer leak.
- modified xlog_finish_iovec() rework to avoid unaligned format objects having
  the same data leak.
- fixed whitespace/long line issues.
- moved the released_space transaction reservation update into
  xlog_cil_insert_items to keep all the CIL commit transaction reservation and
  used space accounting in the one place.
- cleaned up AIL removal of intents on last release.
- factored whiteout cleanup in xlog_cil_push_work() into helper function.

Version 5:
- https://lore.kernel.org/linux-xfs/[e-mail]/
- rebased on 5.18-rc2 + linux-xfs/for-next
- converted transaction flags to unsigned to match tp->t_flags definition

Version 4:
- not published
- rebased on 5.17 + for-next + log shutdown fixes + xlog-write-rework
- fixed memory leak of CUI shadow buffers from log recovery when clearing
  leftover reflink entries.

Version 3:
- https://lore.kernel.org/linux-xfs/[e-mail]/
- rebased on 5.17-rc4 + xlog-write-rework
- no longer dependent on xfs-cil-scalability, so there's some porting changes
  that was needed to remove all the per-cpu CIL dependencies.

Version 2:
- not published
- rebased on 5.15-rc2 + xfs-cil-scalability
- dropped the kvmalloc changes for CIL shadow buffers as that's a
  separate perf problem and not something related to intent
  whiteouts.
- dropped all the delayed attribute modifications so that the
  patchset is not dependent on Allison's dev tree.
- Thanks to Allison for an initial quick review pass - I haven't
  included those RVB tags because every patch in the series has
  changed since the original RFC posting.

RFC:
- https://lore.kernel.org/linux-xfs/[e-mail]/