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Subject[PATCH v5] mm/vmscan: add a fatal signals check in drop_slab_node
From: Chunxin Zang <>

On our server, there are about 10k memcg in one machine. They use memory
very frequently. We have observed that drop_caches can take a
considerable amount of time, and can't stop it.

There are two reasons:
1. There is somebody constantly generating more objects to reclaim
on drop_caches, result the 'freed' always bigger than 10.
2. The process has no chance to process signals.

We can get the following info through 'ps':

root:~# ps -aux | grep drop
root 357956 ... R Aug25 21119854:55 echo 3 > /proc/sys/vm/drop_caches
root 1771385 ... R Aug16 21146421:17 echo 3 > /proc/sys/vm/drop_caches

Add a bail out on the fatal signals in the main loop so that the
operation can be terminated by userspace.

Signed-off-by: Chunxin Zang <>
Signed-off-by: Muchun Song <>
changelogs in v5:
1) v4 patch used wrong branch, very apologies about that.

changelogs in v4:
changelogs in v3:
1) Fix some descriptive problems pointed out by Michal Hocko.
v2 named: mm/vmscan: fix infinite loop in drop_slab_node

changelogs in v2:
1) via check fatal signal break loop.

mm/vmscan.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b6d84326bdf2..c3ed8b45d264 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -704,6 +704,9 @@ void drop_slab_node(int nid)
do {
struct mem_cgroup *memcg = NULL;

+ if (fatal_signal_pending(current))
+ return;
freed = 0;
memcg = mem_cgroup_iter(NULL, NULL, NULL);
do {
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