[PATCH v4 0/4] mm: improve write performance with RWF_DONTCACHE

[Jeff Layton <jlayton@kernel.org>]

Here's a new version for everyone to contemplate while traveling!

This patch series attempts to improve write performance with
RWF_DONTCACHE. The main justification and benchmarks for the series are
in patch #2.

This version implements a scheme that Jan Kara and Christoph Hellwig
suggested during review of the earlier series: after a DONTCACHE write,
kick the flusher thread to do an amount of writeback proportional to the
amount written, but don't target any particular inode or pages when
doing writeback.

The second patch in the series has a summary of the benchmark results.
This seems to markedly improve RWF_DONTCACHE write performance in all
the benchmarks I tested.

The benchmarks I used are in the last two patches. I'm not sure if we
want to merge those into the tree as they are (mostly) AI slop. There
is probably a better tool for this out there.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
Changes in v4:
- Track DONTCACHE dirty pages per bdi_writeback
- New benchmark for competing buffered and dontcache writers
- New benchmark replicating Jens' original 32 concurrent writer test
- Link to v3: https://lore.kernel.org/r/20260426-dontcache-v3-0-79eb37da9547@kernel.org

Changes in v3:
- Track dirty DONTCACHE pages in the VM
- Have flusher write back a proportional number of pages after DONTCACHE write
- Link to v2: https://lore.kernel.org/r/20260408-dontcache-v2-0-948dec1e756b@kernel.org

Changes in v2:
- kick flusher thread instead of initiating writeback inline
- add mechanism to run 'perf lock' around the testcases
- Link to v1: https://lore.kernel.org/r/20260401-dontcache-v1-0-1f5746fab47a@kernel.org

---
Jeff Layton (4):
      mm: track DONTCACHE dirty pages per bdi_writeback
      mm: kick writeback flusher for IOCB_DONTCACHE with targeted dirty tracking
      testing: add nfsd-io-bench NFS server benchmark suite
      testing: add dontcache-bench local filesystem benchmark suite

 fs/fs-writeback.c                                  |  60 ++
 include/linux/backing-dev-defs.h                   |   3 +
 include/linux/fs.h                                 |   6 +-
 include/trace/events/writeback.h                   |   3 +-
 mm/filemap.c                                       |  13 +-
 mm/page-writeback.c                                |   6 +
 .../dontcache-bench/fio-jobs/axboe-write.fio       |  14 +
 .../dontcache-bench/fio-jobs/lat-reader.fio        |  12 +
 .../dontcache-bench/fio-jobs/multi-write.fio       |  11 +
 .../dontcache-bench/fio-jobs/noisy-writer.fio      |  12 +
 .../testing/dontcache-bench/fio-jobs/rand-read.fio |  13 +
 .../dontcache-bench/fio-jobs/rand-write.fio        |  13 +
 .../testing/dontcache-bench/fio-jobs/seq-read.fio  |  13 +
 .../testing/dontcache-bench/fio-jobs/seq-write.fio |  13 +
 .../dontcache-bench/scripts/parse-results.sh       | 346 +++++++++++
 .../dontcache-bench/scripts/run-benchmarks.sh      | 643 +++++++++++++++++++++
 .../testing/nfsd-io-bench/fio-jobs/lat-reader.fio  |  15 +
 .../testing/nfsd-io-bench/fio-jobs/multi-write.fio |  14 +
 .../nfsd-io-bench/fio-jobs/noisy-writer.fio        |  14 +
 tools/testing/nfsd-io-bench/fio-jobs/rand-read.fio |  15 +
 .../testing/nfsd-io-bench/fio-jobs/rand-write.fio  |  15 +
 tools/testing/nfsd-io-bench/fio-jobs/seq-read.fio  |  14 +
 tools/testing/nfsd-io-bench/fio-jobs/seq-write.fio |  14 +
 .../testing/nfsd-io-bench/scripts/parse-results.sh | 238 ++++++++
 .../nfsd-io-bench/scripts/run-benchmarks.sh        | 591 +++++++++++++++++++
 .../testing/nfsd-io-bench/scripts/setup-server.sh  |  94 +++
 26 files changed, 2199 insertions(+), 6 deletions(-)
---
base-commit: 26fd6bff2c050196005312d1d306889220952a99
change-id: 20260401-dontcache-5811efd7eaf3

Best regards,
-- 
Jeff Layton <jlayton@kernel.org>