+ mm-vmscan-add-a-fatal-signals-check-in-drop_slab_node.patch added to -mm tree

+ mm-vmscan-add-a-fatal-signals-check-in-drop_slab_node.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/vmscan: add a fatal signals check in drop_slab_node
has been added to the -mm tree.  Its filename is
     mm-vmscan-add-a-fatal-signals-check-in-drop_slab_node.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-vmscan-add-a-fatal-signals-check-in-drop_slab_node.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-vmscan-add-a-fatal-signals-check-in-drop_slab_node.patch

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------------------------------------------------------
From: Chunxin Zang <zangchunxin@bytedance.com>
Subject: mm/vmscan: add a fatal signals check in drop_slab_node

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.

Link: https://lkml.kernel.org/r/20200916025359.70203-1-zangchunxin@bytedance.com
Signed-off-by: Chunxin Zang <zangchunxin@bytedance.com>
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Chris Down <chris@chrisdown.name>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/mm/vmscan.c~mm-vmscan-add-a-fatal-signals-check-in-drop_slab_node
+++ a/mm/vmscan.c
@@ -702,6 +702,9 @@ void drop_slab_node(int nid)
 		if (fatal_signal_pending(current))
 			return;
 
+		if (fatal_signal_pending(current))
+			return;
+
 		freed = 0;
 		memcg = mem_cgroup_iter(NULL, NULL, NULL);
 		do {
_

Patches currently in -mm which might be from zangchunxin@bytedance.com are

mm-vmscan-fix-infinite-loop-in-drop_slab_node.patch
mm-vmscan-add-a-fatal-signals-check-in-drop_slab_node.patch