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Revert "mm: vmscan: make memcg slab shrink lockless"

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This reverts commit caa05325c9.

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_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/20230609081518.3039120-7-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 08:15:17 +00:00 committed by Andrew Morton
parent d6ecbcd70f
commit 7cee360319
1 changed files with 19 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
mm/vmscan.c
View File

@ -210,21 +210,8 @@ static inline int shrinker_defer_size(int nr_items)
static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
int nid)
{
return srcu_dereference_check(memcg->nodeinfo[nid]->shrinker_info,
&shrinker_srcu,
lockdep_is_held(&shrinker_rwsem));
}
static struct shrinker_info *shrinker_info_srcu(struct mem_cgroup *memcg,
int nid)
{
return srcu_dereference(memcg->nodeinfo[nid]->shrinker_info,
&shrinker_srcu);
}
static void free_shrinker_info_rcu(struct rcu_head *head)
{
kvfree(container_of(head, struct shrinker_info, rcu));
return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
lockdep_is_held(&shrinker_rwsem));
}
static int expand_one_shrinker_info(struct mem_cgroup *memcg,
@ -265,7 +252,7 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
defer_size - old_defer_size);
rcu_assign_pointer(pn->shrinker_info, new);
call_srcu(&shrinker_srcu, &old->rcu, free_shrinker_info_rcu);
kvfree_rcu(old, rcu);
}
return 0;
@ -351,16 +338,15 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
{
if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
struct shrinker_info *info;
int srcu_idx;
srcu_idx = srcu_read_lock(&shrinker_srcu);
info = shrinker_info_srcu(memcg, nid);
rcu_read_lock();
info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
/* Pairs with smp mb in shrink_slab() */
smp_mb__before_atomic();
set_bit(shrinker_id, info->map);
}
srcu_read_unlock(&shrinker_srcu, srcu_idx);
rcu_read_unlock();
}
}
@ -374,6 +360,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
return -ENOSYS;
down_write(&shrinker_rwsem);
/* This may call shrinker, so it must use down_read_trylock() */
id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
if (id < 0)
goto unlock;
@ -407,7 +394,7 @@ static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
{
struct shrinker_info *info;
info = shrinker_info_srcu(memcg, nid);
info = shrinker_info_protected(memcg, nid);
return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
}
@ -416,7 +403,7 @@ static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
{
struct shrinker_info *info;
info = shrinker_info_srcu(memcg, nid);
info = shrinker_info_protected(memcg, nid);
return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
}
@ -947,14 +934,15 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
{
struct shrinker_info *info;
unsigned long ret, freed = 0;
int srcu_idx;
int i;
if (!mem_cgroup_online(memcg))
return 0;
srcu_idx = srcu_read_lock(&shrinker_srcu);
info = shrinker_info_srcu(memcg, nid);
if (!down_read_trylock(&shrinker_rwsem))
return 0;
info = shrinker_info_protected(memcg, nid);
if (unlikely(!info))
goto unlock;
@ -1004,9 +992,14 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
set_shrinker_bit(memcg, nid, i);
}
freed += ret;
if (rwsem_is_contended(&shrinker_rwsem)) {
freed = freed ? : 1;
break;
}
}
unlock:
srcu_read_unlock(&shrinker_srcu, srcu_idx);
up_read(&shrinker_rwsem);
return freed;
}
#else /* CONFIG_MEMCG */