commit 47a7c01c3efc6581f5dcca40928baeb38e1e40c2
author Qi Zheng <zhengqi.arch@bytedance.com> Fri Jun 09 08:15:12 2023 +0000
committer Andrew Morton <akpm@linux-foundation.org> Mon Jun 19 13:19:33 2023 -0700
tree 00073c63c91b68b1fb45cb3cdbeb9aee5c396945
parent 679bd7ebdd315bf457a4740b306ae99f1d0a403d

Revert "mm: shrinkers: convert shrinker_rwsem to mutex"

Patch series "revert shrinker_srcu related changes".


This patch (of 7):

This reverts commit cf2e309ebca7bb0916771839f9b580b06c778530.

Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec
test case [1], which is caused by commit f95bdb700bc6 ("mm: vmscan: make
global slab shrink lockless").  The root cause is that SRCU has to be
careful to not frequently check for SRCU read-side critical section exits.
Therefore, even if no one is currently in the SRCU read-side critical
section, synchronize_srcu() cannot return quickly.  That's why
unregister_shrinker() has become slower.

After discussion, we will try to use the refcount+RCU method [2] proposed
by Dave Chinner to continue to re-implement the lockless slab shrink.  So
revert the shrinker_mutex back to shrinker_rwsem first.

[1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/
[2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/

Link: https://lkml.kernel.org/r/20230609081518.3039120-1-qi.zheng@linux.dev
Link: https://lkml.kernel.org/r/20230609081518.3039120-2-qi.zheng@linux.dev
Reported-by: kernel test robot <yujie.liu@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@intel.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Kirill Tkhai <tkhai@ya.ru>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yujie Liu <yujie.liu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>