On Tue 15-09-20 19:40:01, zangchunxin@xxxxxxxxxxxxx wrote:
> From: Chunxin Zang <zangchunxin@xxxxxxxxxxxxx>
>
> 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
> root 1986319 ... R 18:56 117:27 echo 3 > /proc/sys/vm/drop_caches
> root 2002148 ... R Aug24 5720:39 echo 3 > /proc/sys/vm/drop_caches
> root 2564666 ... R 18:59 113:58 echo 3 > /proc/sys/vm/drop_caches
> root 2639347 ... R Sep03 2383:39 echo 3 > /proc/sys/vm/drop_caches
> root 3904747 ... R 03:35 993:31 echo 3 > /proc/sys/vm/drop_caches
> root 4016780 ... R Aug21 7882:18 echo 3 > /proc/sys/vm/drop_caches
>
> Use bpftrace follow 'freed' value in drop_slab_node:
>
> root:~# bpftrace -e 'kprobe:drop_slab_node+70 {@ret=hist(reg("bp")); }'
> Attaching 1 probe...
> ^B^C
>
> @ret:
> [64, 128) 1 | |
> [128, 256) 28 | |
> [256, 512) 107 |@ |
> [512, 1K) 298 |@@@ |
> [1K, 2K) 613 |@@@@@@@ |
> [2K, 4K) 4435 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> [4K, 8K) 442 |@@@@@ |
> [8K, 16K) 299 |@@@ |
> [16K, 32K) 100 |@ |
> [32K, 64K) 139 |@ |
> [64K, 128K) 56 | |
> [128K, 256K) 26 | |
> [256K, 512K) 2 | |
I am not sure this is very helpful for this patch but whatever.
> We need one path to stop the process.
I would use the following instead
"
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 <zangchunxin@xxxxxxxxxxxxx>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>
> changelogs in v3:
> 1) update the description of the patch.
> 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..6b2b5d420510 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 (signal_pending(current))
> + return;
> +
> freed = 0;
> memcg = mem_cgroup_iter(NULL, NULL, NULL);
> do {
> --
> 2.11.0
>
--
Michal Hocko
SUSE Labs
