[PATCH v4 0/9] Generic per-sb io stats

[Amir Goldstein <amir73il@gmail.com>]

Miklos,

I ran some micro benchmarks on v3 patch [1] which demonstrated up to
20% slowdown for some workloads (many small reads/writes in a small VM).
This revision adds the "relaxed" percpu counter helpers to mitigate
the iostats counters overhead.

With the relaxed counters, the micro benchmarks that I ran did not
demonstrate any measurable overhead on xfs, on overlayfs over xfs
and overlayfs over tmpfs.

Dave Chinner asked why the io stats should not be enabled for all
filesystems.  That change seems too bold for me so instead, I included
an extra patch to auto-enable per-sb io stats for blockdev filesystems.

Should you decide to take the patches for enabling io stats for
overlayfs and/or fuse through your tree, it is up to you to whether you
want to take this patch as well or leave it out until more people have
a chance to test it and run more performance tests on their setups.

Thanks,
Amir.

[1] https://lore.kernel.org/linux-fsdevel/20220301184221.371853-1-amir73il@gmail.com/

Changes since v3:
- Use "relaxed" counters to reduce performance overhead
- Opt-in to per-sb io stats via fs_flags (dchinner)
- Add patch to auto-enable io stats for all blockdev fs (dchinner)

Changes since v2:
- Change from per-mount to per-sb io stats (szeredi)
- Avoid percpu loop when reading mountstats (dchinner)

Changes since v1:
- Opt-in for per-mount io stats for overlayfs and fuse

Amir Goldstein (9):
  lib/percpu_counter: add helpers for "relaxed" counters
  lib/percpu_counter: add helpers for arrays of counters
  fs: tidy up fs_flags definitions
  fs: add optional iostats counters to struct super_block
  fs: collect per-sb io stats
  fs: report per-sb io stats
  ovl: opt-in for per-sb io stats
  fuse: opt-in for per-sb io stats
  fs: enable per-sb io stats for all blockdev filesystems

 fs/Kconfig                     |   8 ++
 fs/fuse/inode.c                |   3 +-
 fs/nfsd/export.c               |  10 ++-
 fs/nfsd/nfscache.c             |   5 +-
 fs/nfsd/stats.c                |  37 +---------
 fs/nfsd/stats.h                |   3 -
 fs/overlayfs/super.c           |   3 +-
 fs/proc_namespace.c            |  16 ++++
 fs/read_write.c                |  88 ++++++++++++++++------
 fs/super.c                     |  11 +++
 include/linux/fs.h             |  25 ++++---
 include/linux/fs_iostats.h     | 130 +++++++++++++++++++++++++++++++++
 include/linux/percpu_counter.h |  48 ++++++++++++
 lib/percpu_counter.c           |  27 +++++++
 14 files changed, 337 insertions(+), 77 deletions(-)
 create mode 100644 include/linux/fs_iostats.h

-- 
2.25.1