[PATCH v4 0/3] fs/dcache: Track # of negative dentries

From: Waiman Long
Date: Wed Sep 12 2018 - 13:36:14 EST

- Drop patch 4 as it is just a minor optimization.
- Add a cc:stable tag to patch 1.
- Clean up some comments in patch 3.

- With confirmation that the dummy array in dentry_stat structure
was never a replacement of a previously used field, patch 3 is now
reverted back to use one of dummy field as the negative dentry count
instead of adding a new field.

- Clarify what the new nr_dentry_negative per-cpu counter is tracking
and open-code the increment and decrement as suggested by Dave Chinner.
- Append the new nr_dentry_negative count as the 7th element of dentry-state
instead of replacing one of the dummy entries.
- Remove patch "fs/dcache: Make negative dentries easier to be
reclaimed" for now as I need more time to think about what
to do with it.
- Add 2 more patches to address issues found while reviewing the
dentry code.
- Add another patch to change the conditional branch of
nr_dentry_negative accounting to conditional move so as to reduce
the performance impact of the accounting code.

This patchset addresses 2 issues found in the dentry code and adds a
new nr_dentry_negative per-cpu counter to track the total number of
negative dentries in all the LRU lists.

Patch 1 fixes a bug in the accounting of nr_dentry_unused in

Patch 2 removes the ____cacheline_aligned_in_smp tag from super_block
LRU lists.

Patch 3 adds the new nr_dentry_negative per-cpu counter.

Various filesystem related tests were run and no statistically
significant changes in performance outside of the possible noise range
was observed.

Waiman Long (3):
fs/dcache: Fix incorrect nr_dentry_unused accounting in
fs: Don't need to put list_lru into its own cacheline
fs/dcache: Track & report number of negative dentries

Documentation/sysctl/fs.txt | 26 ++++++++++++++++----------
fs/dcache.c | 38 +++++++++++++++++++++++++++++++++-----
include/linux/dcache.h | 7 ++++---
include/linux/fs.h | 9 +++++----
4 files changed, 58 insertions(+), 22 deletions(-)