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Revert "mm: vmscan: add shrinker_srcu_generation"

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This reverts commit 475733dda5.

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.

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_srcu related changes 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/20230609081518.3039120-6-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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Qi Zheng 2023-06-09 08:15:16 +00:00 committed by Andrew Morton
parent 1a554ecc97
commit d6ecbcd70f
1 changed files with 4 additions and 20 deletions
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24
mm/vmscan.c
View file

@ -192,7 +192,6 @@ int vm_swappiness = 60;
LIST_HEAD(shrinker_list);
DECLARE_RWSEM(shrinker_rwsem);
DEFINE_SRCU(shrinker_srcu);
static atomic_t shrinker_srcu_generation = ATOMIC_INIT(0);
#ifdef CONFIG_MEMCG
static int shrinker_nr_max;
@ -818,7 +817,6 @@ void unregister_shrinker(struct shrinker *shrinker)
debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
up_write(&shrinker_rwsem);
atomic_inc(&shrinker_srcu_generation);
synchronize_srcu(&shrinker_srcu);
shrinker_debugfs_remove(debugfs_entry, debugfs_id);
@ -840,7 +838,6 @@ void synchronize_shrinkers(void)
{
down_write(&shrinker_rwsem);
up_write(&shrinker_rwsem);
atomic_inc(&shrinker_srcu_generation);
synchronize_srcu(&shrinker_srcu);
}
EXPORT_SYMBOL(synchronize_shrinkers);
@ -950,20 +947,18 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
{
struct shrinker_info *info;
unsigned long ret, freed = 0;
int srcu_idx, generation;
int i = 0;
int srcu_idx;
int i;
if (!mem_cgroup_online(memcg))
return 0;
again:
srcu_idx = srcu_read_lock(&shrinker_srcu);
info = shrinker_info_srcu(memcg, nid);
if (unlikely(!info))
goto unlock;
generation = atomic_read(&shrinker_srcu_generation);
for_each_set_bit_from(i, info->map, info->map_nr_max) {
for_each_set_bit(i, info->map, info->map_nr_max) {
struct shrink_control sc = {
.gfp_mask = gfp_mask,
.nid = nid,
@ -1009,11 +1004,6 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
set_shrinker_bit(memcg, nid, i);
}
freed += ret;
if (atomic_read(&shrinker_srcu_generation) != generation) {
srcu_read_unlock(&shrinker_srcu, srcu_idx);
i++;
goto again;
}
}
unlock:
srcu_read_unlock(&shrinker_srcu, srcu_idx);
@ -1053,7 +1043,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
{
unsigned long ret, freed = 0;
struct shrinker *shrinker;
int srcu_idx, generation;
int srcu_idx;
/*
* The root memcg might be allocated even though memcg is disabled
@ -1067,7 +1057,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
srcu_idx = srcu_read_lock(&shrinker_srcu);
generation = atomic_read(&shrinker_srcu_generation);
list_for_each_entry_srcu(shrinker, &shrinker_list, list,
srcu_read_lock_held(&shrinker_srcu)) {
struct shrink_control sc = {
@ -1080,11 +1069,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
if (ret == SHRINK_EMPTY)
ret = 0;
freed += ret;
if (atomic_read(&shrinker_srcu_generation) != generation) {
freed = freed ? : 1;
break;
}
}
srcu_read_unlock(&shrinker_srcu, srcu_idx);