[PATCH v3 0/4] mm: improve write performance with RWF_DONTCACHE

Jeff Layton
2026-04-26T11:56:39Z

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 work as well or better than the earlier approaches.

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 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: add NR_DONTCACHE_DIRTY node page counter
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 | 2 +
include/linux/fs.h | 6 +-
include/linux/mmzone.h | 1 +
include/trace/events/writeback.h | 3 +-
mm/filemap.c | 6 +-
mm/page-writeback.c | 7 +
mm/vmstat.c | 1 +
.../dontcache-bench/fio-jobs/lat-reader.fio | 12 +
.../dontcache-bench/fio-jobs/multi-write.fio | 9 +
.../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 | 238 +++++++++
.../dontcache-bench/scripts/run-benchmarks.sh | 562 ++++++++++++++++++++
.../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 ++++
27 files changed, 1989 insertions(+), 6 deletions(-)
---
base-commit: 27d128c1cff64c3b8012cc56dd5a1391bb4f1821
change-id: 20260401-dontcache-5811efd7eaf3

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