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mm: vmscan: make memcg slab shrink lockless

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Like global slab shrink, this commit also uses SRCU to make memcg slab
shrink lockless.

We can reproduce the down_read_trylock() hotspot through the
following script:

```

DIR="/root/shrinker/memcg/mnt"

do_create()
{
    mkdir -p /sys/fs/cgroup/memory/test
    mkdir -p /sys/fs/cgroup/perf_event/test
    echo 4G > /sys/fs/cgroup/memory/test/memory.limit_in_bytes
    for i in `seq 0 $1`;
    do
        mkdir -p /sys/fs/cgroup/memory/test/$i;
        echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
        echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs;
        mkdir -p $DIR/$i;
    done
}

do_mount()
{
    for i in `seq $1 $2`;
    do
        mount -t tmpfs $i $DIR/$i;
    done
}

do_touch()
{
    for i in `seq $1 $2`;
    do
        echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
        echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs;
            dd if=/dev/zero of=$DIR/$i/file$i bs=1M count=1 &
    done
}

case "$1" in
  touch)
    do_touch $2 $3
    ;;
  test)
      do_create 4000
    do_mount 0 4000
    do_touch 0 3000
    ;;
  *)
    exit 1
    ;;
esac
```

Save the above script, then run test and touch commands.
Then we can use the following perf command to view hotspots:

perf top -U -F 999

1) Before applying this patchset:

  32.31%  [kernel]           [k] down_read_trylock
  19.40%  [kernel]           [k] pv_native_safe_halt
  16.24%  [kernel]           [k] up_read
  15.70%  [kernel]           [k] shrink_slab
   4.69%  [kernel]           [k] _find_next_bit
   2.62%  [kernel]           [k] shrink_node
   1.78%  [kernel]           [k] shrink_lruvec
   0.76%  [kernel]           [k] do_shrink_slab

2) After applying this patchset:

  27.83%  [kernel]           [k] _find_next_bit
  16.97%  [kernel]           [k] shrink_slab
  15.82%  [kernel]           [k] pv_native_safe_halt
   9.58%  [kernel]           [k] shrink_node
   8.31%  [kernel]           [k] shrink_lruvec
   5.64%  [kernel]           [k] do_shrink_slab
   3.88%  [kernel]           [k] mem_cgroup_iter

At the same time, we use the following perf command to capture
IPC information:

perf stat -e cycles,instructions -G test -a --repeat 5 -- sleep 10

1) Before applying this patchset:

 Performance counter stats for 'system wide' (5 runs):

      454187219766      cycles                    test                    ( +-  1.84% )
       78896433101      instructions              test #    0.17  insn per cycle           ( +-  0.44% )

        10.0020430 +- 0.0000366 seconds time elapsed  ( +-  0.00% )

2) After applying this patchset:

 Performance counter stats for 'system wide' (5 runs):

      841954709443      cycles                    test                    ( +- 15.80% )  (98.69%)
      527258677936      instructions              test #    0.63  insn per cycle           ( +- 15.11% )  (98.68%)

          10.01064 +- 0.00831 seconds time elapsed  ( +-  0.08% )

We can see that IPC drops very seriously when calling
down_read_trylock() at high frequency. After using SRCU,
the IPC is at a normal level.

Link: https://lkml.kernel.org/r/20230313112819.38938-4-zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Kirill Tkhai <tkhai@ya.ru>
Acked-by: Vlastimil Babka <Vbabka@suse.cz>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Christian König <christian.koenig@amd.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sultan Alsawaf <sultan@kerneltoast.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Qi Zheng 2023-03-13 19:28:14 +08:00 committed by Andrew Morton
parent f95bdb700b
commit caa05325c9
1 changed files with 26 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
mm/vmscan.c
View File

@ -222,8 +222,21 @@ static inline int shrinker_defer_size(int nr_items)
static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
int nid)
{
return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
lockdep_is_held(&shrinker_rwsem));
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));
}
static int expand_one_shrinker_info(struct mem_cgroup *memcg,
@ -264,7 +277,7 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
defer_size - old_defer_size);
rcu_assign_pointer(pn->shrinker_info, new);
kvfree_rcu(old, rcu);
call_srcu(&shrinker_srcu, &old->rcu, free_shrinker_info_rcu);
}
return 0;
@ -350,15 +363,16 @@ 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;
rcu_read_lock();
info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
srcu_idx = srcu_read_lock(&shrinker_srcu);
info = shrinker_info_srcu(memcg, nid);
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);
}
rcu_read_unlock();
srcu_read_unlock(&shrinker_srcu, srcu_idx);
}
}
@ -372,7 +386,6 @@ 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;
@ -406,7 +419,7 @@ static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
{
struct shrinker_info *info;
info = shrinker_info_protected(memcg, nid);
info = shrinker_info_srcu(memcg, nid);
return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
}
@ -415,7 +428,7 @@ static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
{
struct shrinker_info *info;
info = shrinker_info_protected(memcg, nid);
info = shrinker_info_srcu(memcg, nid);
return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
}
@ -893,15 +906,14 @@ 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;
if (!down_read_trylock(&shrinker_rwsem))
return 0;
info = shrinker_info_protected(memcg, nid);
srcu_idx = srcu_read_lock(&shrinker_srcu);
info = shrinker_info_srcu(memcg, nid);
if (unlikely(!info))
goto unlock;
@ -951,14 +963,9 @@ 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:
up_read(&shrinker_rwsem);
srcu_read_unlock(&shrinker_srcu, srcu_idx);
return freed;
}
#else /* CONFIG_MEMCG */