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Revert "mm: shrinkers: convert shrinker_rwsem to mutex"

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Patch series "revert shrinker_srcu related changes".


This patch (of 7):

This reverts commit cf2e309ebc.

Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec
test case [1], which is caused by commit f95bdb700b ("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>
This commit is contained in:
Qi Zheng
2023-06-09 08:15:12 +00:00
committed by Andrew Morton
parent 679bd7ebdd
commit 47a7c01c3e
5 changed files with 27 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
mm/shrinker_debug.c
View File

@@ -8,7 +8,7 @@
#include <linux/srcu.h>
/* defined in vmscan.c */
extern struct mutex shrinker_mutex;
extern struct rw_semaphore shrinker_rwsem;
extern struct list_head shrinker_list;
extern struct srcu_struct shrinker_srcu;
@@ -168,7 +168,7 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
char buf[128];
int id;
lockdep_assert_held(&shrinker_mutex);
lockdep_assert_held(&shrinker_rwsem);
/* debugfs isn't initialized yet, add debugfs entries later. */
if (!shrinker_debugfs_root)
@@ -211,7 +211,7 @@ int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
if (!new)
return -ENOMEM;
mutex_lock(&shrinker_mutex);
down_write(&shrinker_rwsem);
old = shrinker->name;
shrinker->name = new;
@@ -229,7 +229,7 @@ int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
shrinker->debugfs_entry = entry;
}
mutex_unlock(&shrinker_mutex);
up_write(&shrinker_rwsem);
kfree_const(old);
@@ -242,7 +242,7 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
{
struct dentry *entry = shrinker->debugfs_entry;
lockdep_assert_held(&shrinker_mutex);
lockdep_assert_held(&shrinker_rwsem);
kfree_const(shrinker->name);
shrinker->name = NULL;
@@ -271,14 +271,14 @@ static int __init shrinker_debugfs_init(void)
shrinker_debugfs_root = dentry;
/* Create debugfs entries for shrinkers registered at boot */
mutex_lock(&shrinker_mutex);
down_write(&shrinker_rwsem);
list_for_each_entry(shrinker, &shrinker_list, list)
if (!shrinker->debugfs_entry) {
ret = shrinker_debugfs_add(shrinker);
if (ret)
break;
}
mutex_unlock(&shrinker_mutex);
up_write(&shrinker_rwsem);
return ret;
}