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authorQi Zheng <zhengqi.arch@bytedance.com>2023-03-13 19:28:14 +0800
committerAndrew Morton <akpm@linux-foundation.org>2023-03-28 16:20:16 -0700
commitcaa05325c9126c77ebf114edce51536a0d0a9a08 (patch)
treec15ae80d13ca7c6d95c48e978c7c040f527bfb7d /mm/vmscan.c
parentf95bdb700bc6bb74e1199b1f5f90c613e152cfa7 (diff)
mm: vmscan: make memcg slab shrink lockless
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>
Diffstat (limited to 'mm/vmscan.c')
-rw-r--r--mm/vmscan.c45
1 files changed, 26 insertions, 19 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index db2ed6e08f67..ce7834030f75 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -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 */