| Message ID | 20200915114001.79950-1-zangchunxin@bytedance.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] mm/vmscan: add a fatal signals check in drop_slab_node | expand |
On Tue 15-09-20 19:40:01, zangchunxin@bytedance.com wrote: > From: Chunxin Zang <zangchunxin@bytedance.com> > > 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@bytedance.com> > Signed-off-by: Muchun Song <songmuchun@bytedance.com> Acked-by: Michal Hocko <mhocko@suse.com> > --- > > 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 >
On Tue, Sep 15, 2020 at 8:13 PM Michal Hocko <mhocko@suse.com> wrote: > > On Tue 15-09-20 19:40:01, zangchunxin@bytedance.com wrote: > > From: Chunxin Zang <zangchunxin@bytedance.com> > > > > 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. > Yes, it looks a bit messy, I will delete that. > > 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. > " > Thanks, will do that :) > > > > Signed-off-by: Chunxin Zang <zangchunxin@bytedance.com> > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > > Acked-by: Michal Hocko <mhocko@suse.com> > > > --- > > > > 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 Best wishes Chunxin
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 {