* [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup
@ 2020-08-26 13:47 Xunlei Pang
2020-08-26 14:10 ` Chris Down
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Xunlei Pang @ 2020-08-26 13:47 UTC (permalink / raw)
To: Johannes Weiner, Michal Hocko, Andrew Morton, Vladimir Davydov
Cc: Xunlei Pang, linux-kernel, linux-mm
We've met softlockup with "CONFIG_PREEMPT_NONE=y", when
the target memcg doesn't have any reclaimable memory.
It can be easily reproduced as below:
watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204]
CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12
Call Trace:
shrink_lruvec+0x49f/0x640
shrink_node+0x2a6/0x6f0
do_try_to_free_pages+0xe9/0x3e0
try_to_free_mem_cgroup_pages+0xef/0x1f0
try_charge+0x2c1/0x750
mem_cgroup_charge+0xd7/0x240
__add_to_page_cache_locked+0x2fd/0x370
add_to_page_cache_lru+0x4a/0xc0
pagecache_get_page+0x10b/0x2f0
filemap_fault+0x661/0xad0
ext4_filemap_fault+0x2c/0x40
__do_fault+0x4d/0xf9
handle_mm_fault+0x1080/0x1790
It only happens on our 1-vcpu instances, because there's no chance
for oom reaper to run to reclaim the to-be-killed process.
Add cond_resched() at the upper shrink_node_memcgs() to solve this
issue, and any other possible issue like meomry.min protection.
Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
---
mm/vmscan.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 99e1796..bbdc38b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2617,6 +2617,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
mem_cgroup_calculate_protection(target_memcg, memcg);
+ cond_resched();
+
if (mem_cgroup_below_min(memcg)) {
/*
* Hard protection.
--
1.8.3.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup
2020-08-26 13:47 [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup Xunlei Pang
@ 2020-08-26 14:10 ` Chris Down
2020-08-26 18:17 ` Chris Down
2020-08-26 15:05 ` Michal Hocko
2020-08-26 16:43 ` Johannes Weiner
2 siblings, 1 reply; 6+ messages in thread
From: Chris Down @ 2020-08-26 14:10 UTC (permalink / raw)
To: Xunlei Pang
Cc: Johannes Weiner, Michal Hocko, Andrew Morton, Vladimir Davydov,
linux-kernel, linux-mm
Hi Xunlei,
Xunlei Pang writes:
>Add cond_resched() at the upper shrink_node_memcgs() to solve this
>issue, and any other possible issue like meomry.min protection.
I understand the general intent of the patch, but could you clarify your
concern around memory protection?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup
2020-08-26 13:47 [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup Xunlei Pang
2020-08-26 14:10 ` Chris Down
@ 2020-08-26 15:05 ` Michal Hocko
2020-08-26 16:43 ` Johannes Weiner
2 siblings, 0 replies; 6+ messages in thread
From: Michal Hocko @ 2020-08-26 15:05 UTC (permalink / raw)
To: Xunlei Pang
Cc: Johannes Weiner, Andrew Morton, Vladimir Davydov, linux-kernel, linux-mm
On Wed 26-08-20 21:47:02, Xunlei Pang wrote:
> We've met softlockup with "CONFIG_PREEMPT_NONE=y", when
> the target memcg doesn't have any reclaimable memory.
>
> It can be easily reproduced as below:
> watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204]
> CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12
> Call Trace:
> shrink_lruvec+0x49f/0x640
> shrink_node+0x2a6/0x6f0
> do_try_to_free_pages+0xe9/0x3e0
> try_to_free_mem_cgroup_pages+0xef/0x1f0
> try_charge+0x2c1/0x750
> mem_cgroup_charge+0xd7/0x240
> __add_to_page_cache_locked+0x2fd/0x370
> add_to_page_cache_lru+0x4a/0xc0
> pagecache_get_page+0x10b/0x2f0
> filemap_fault+0x661/0xad0
> ext4_filemap_fault+0x2c/0x40
> __do_fault+0x4d/0xf9
> handle_mm_fault+0x1080/0x1790
>
> It only happens on our 1-vcpu instances, because there's no chance
> for oom reaper to run to reclaim the to-be-killed process.
>
> Add cond_resched() at the upper shrink_node_memcgs() to solve this
> issue, and any other possible issue like meomry.min protection.
I would just add
"
This will mean that we will get a scheduling point for each memcg in the
reclaimed hierarchy without any dependency on the reclaimable memory in
that memcg thus making it more predictable.
"
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!
> ---
> mm/vmscan.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 99e1796..bbdc38b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2617,6 +2617,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
>
> mem_cgroup_calculate_protection(target_memcg, memcg);
>
> + cond_resched();
> +
> if (mem_cgroup_below_min(memcg)) {
> /*
> * Hard protection.
> --
> 1.8.3.1
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup
2020-08-26 13:47 [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup Xunlei Pang
2020-08-26 14:10 ` Chris Down
2020-08-26 15:05 ` Michal Hocko
@ 2020-08-26 16:43 ` Johannes Weiner
2020-08-26 17:29 ` Michal Hocko
2 siblings, 1 reply; 6+ messages in thread
From: Johannes Weiner @ 2020-08-26 16:43 UTC (permalink / raw)
To: Xunlei Pang
Cc: Michal Hocko, Andrew Morton, Vladimir Davydov, linux-kernel, linux-mm
On Wed, Aug 26, 2020 at 09:47:02PM +0800, Xunlei Pang wrote:
> We've met softlockup with "CONFIG_PREEMPT_NONE=y", when
> the target memcg doesn't have any reclaimable memory.
>
> It can be easily reproduced as below:
> watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204]
> CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12
> Call Trace:
> shrink_lruvec+0x49f/0x640
> shrink_node+0x2a6/0x6f0
> do_try_to_free_pages+0xe9/0x3e0
> try_to_free_mem_cgroup_pages+0xef/0x1f0
> try_charge+0x2c1/0x750
> mem_cgroup_charge+0xd7/0x240
> __add_to_page_cache_locked+0x2fd/0x370
> add_to_page_cache_lru+0x4a/0xc0
> pagecache_get_page+0x10b/0x2f0
> filemap_fault+0x661/0xad0
> ext4_filemap_fault+0x2c/0x40
> __do_fault+0x4d/0xf9
> handle_mm_fault+0x1080/0x1790
>
> It only happens on our 1-vcpu instances, because there's no chance
> for oom reaper to run to reclaim the to-be-killed process.
>
> Add cond_resched() at the upper shrink_node_memcgs() to solve this
> issue, and any other possible issue like meomry.min protection.
>
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
This generally makes sense to me but really should have a comment:
/*
* This loop can become CPU-bound when there are thousands
* of cgroups that aren't eligible for reclaim - either
* because they don't have any pages, or because their
* memory is explicitly protected. Avoid soft lockups.
*/
cond_resched();
The placement in the middle of the multi-part protection checks is a
bit odd too. It would be better to have it either at the top of the
loop, or at the end, by replacing the continues with goto next.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup
2020-08-26 16:43 ` Johannes Weiner
@ 2020-08-26 17:29 ` Michal Hocko
0 siblings, 0 replies; 6+ messages in thread
From: Michal Hocko @ 2020-08-26 17:29 UTC (permalink / raw)
To: Johannes Weiner
Cc: Xunlei Pang, Andrew Morton, Vladimir Davydov, linux-kernel, linux-mm
On Wed 26-08-20 12:43:32, Johannes Weiner wrote:
> On Wed, Aug 26, 2020 at 09:47:02PM +0800, Xunlei Pang wrote:
> > We've met softlockup with "CONFIG_PREEMPT_NONE=y", when
> > the target memcg doesn't have any reclaimable memory.
> >
> > It can be easily reproduced as below:
> > watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204]
> > CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12
> > Call Trace:
> > shrink_lruvec+0x49f/0x640
> > shrink_node+0x2a6/0x6f0
> > do_try_to_free_pages+0xe9/0x3e0
> > try_to_free_mem_cgroup_pages+0xef/0x1f0
> > try_charge+0x2c1/0x750
> > mem_cgroup_charge+0xd7/0x240
> > __add_to_page_cache_locked+0x2fd/0x370
> > add_to_page_cache_lru+0x4a/0xc0
> > pagecache_get_page+0x10b/0x2f0
> > filemap_fault+0x661/0xad0
> > ext4_filemap_fault+0x2c/0x40
> > __do_fault+0x4d/0xf9
> > handle_mm_fault+0x1080/0x1790
> >
> > It only happens on our 1-vcpu instances, because there's no chance
> > for oom reaper to run to reclaim the to-be-killed process.
> >
> > Add cond_resched() at the upper shrink_node_memcgs() to solve this
> > issue, and any other possible issue like meomry.min protection.
> >
> > Suggested-by: Michal Hocko <mhocko@suse.com>
> > Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
>
> This generally makes sense to me but really should have a comment:
>
> /*
> * This loop can become CPU-bound when there are thousands
> * of cgroups that aren't eligible for reclaim - either
> * because they don't have any pages, or because their
> * memory is explicitly protected. Avoid soft lockups.
> */
> cond_resched();
>
> The placement in the middle of the multi-part protection checks is a
> bit odd too. It would be better to have it either at the top of the
> loop, or at the end, by replacing the continues with goto next.
Yes makes sense. I would stick it to the begining of the loop to make it
stand out and make it obvious wrt code flow.
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup
2020-08-26 14:10 ` Chris Down
@ 2020-08-26 18:17 ` Chris Down
0 siblings, 0 replies; 6+ messages in thread
From: Chris Down @ 2020-08-26 18:17 UTC (permalink / raw)
To: Xunlei Pang
Cc: Johannes Weiner, Michal Hocko, Andrew Morton, Vladimir Davydov,
linux-kernel, linux-mm
Chris Down writes:
>Xunlei Pang writes:
>>Add cond_resched() at the upper shrink_node_memcgs() to solve this
>>issue, and any other possible issue like meomry.min protection.
>
>I understand the general intent of the patch, but could you clarify
>your concern around memory protection?
Oh, I see, your concern is just preemption in general rather than a fixing
anything for the memory protection side. In which case, go for it, but I agree
with Michael that it would be nice to send v3 with a clarifying comment.
Acked-by: Chris Down <chris@chrisdown.name>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-08-26 18:20 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-26 13:47 [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup Xunlei Pang
2020-08-26 14:10 ` Chris Down
2020-08-26 18:17 ` Chris Down
2020-08-26 15:05 ` Michal Hocko
2020-08-26 16:43 ` Johannes Weiner
2020-08-26 17:29 ` Michal Hocko
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