The quilt patch titled
Subject: mm: vmscan: make memcg slab shrink lockless
has been removed from the -mm tree. Its filename was
mm-vmscan-make-memcg-slab-shrink-lockless.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Subject: mm: vmscan: make memcg slab shrink lockless
Date: Mon, 13 Mar 2023 19:28:14 +0800
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@xxxxxxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Acked-by: Kirill Tkhai <tkhai@xxxxx>
Acked-by: Vlastimil Babka <Vbabka@xxxxxxx>
Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 45 ++++++++++++++++++++++++++-------------------
1 file changed, 26 insertions(+), 19 deletions(-)
--- a/mm/vmscan.c~mm-vmscan-make-memcg-slab-shrink-lockless
+++ a/mm/vmscan.c
@@ -222,8 +222,21 @@ static inline int shrinker_defer_size(in
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(stru
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
{
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(struc
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 n
{
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 n
{
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(g
{
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(g
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 */
_
Patches currently in -mm which might be from zhengqi.arch@xxxxxxxxxxxxx are
