[Devel] [PATCH rh7 1/2] mm: memcg: fix memcg reclaim soft lockup

2021-02-01 Thread Andrey Ryabinin 
From: Xunlei Pang 

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 a cond_resched() at the upper shrink_node_memcgs() to solve this
issue, 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 
Signed-off-by: Xunlei Pang 
Signed-off-by: Andrew Morton 
Acked-by: Chris Down 
Acked-by: Michal Hocko 
Acked-by: Johannes Weiner 
Link: 
http://lkml.kernel.org/r/1598495549-67324-1-git-send-email-xlp...@linux.alibaba.com
Signed-off-by: Linus Torvalds 

https://jira.sw.ru/browse/PSBM-125095
(cherry picked from commit e3336cab2579012b1e72b5265adf98e2d6e244ad)
Signed-off-by: Andrey Ryabinin 
---
 mm/vmscan.c | 8 
 1 file changed, 8 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 85622f235e78..080500f4e366 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2684,6 +2684,14 @@ static void shrink_zone(struct zone *zone, struct 
scan_control *sc,
do {
unsigned long lru_pages, scanned;
 
+   /*
+* This loop can become CPU-bound when target memcgs
+* aren't eligible for reclaim - either because they
+* don't have any reclaimable pages, or because their
+* memory is explicitly protected. Avoid soft lockups.
+*/
+   cond_resched();
+
if (!sc->may_thrash && mem_cgroup_low(root, memcg))
continue;
 
-- 
2.26.2

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Re: [Devel] [PATCH rh7 1/2] mm: memcg: fix memcg reclaim soft lockup

2021-02-02 Thread Kirill Tkhai 
On 01.02.2021 17:10, Andrey Ryabinin wrote:
> From: Xunlei Pang 
> 
> 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 a cond_resched() at the upper shrink_node_memcgs() to solve this
> issue, 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 
> Signed-off-by: Xunlei Pang 
> Signed-off-by: Andrew Morton 
> Acked-by: Chris Down 
> Acked-by: Michal Hocko 
> Acked-by: Johannes Weiner 
> Link: 
> http://lkml.kernel.org/r/1598495549-67324-1-git-send-email-xlp...@linux.alibaba.com
> Signed-off-by: Linus Torvalds 

Reviewed-by: Kirill Tkhai 

> 
> https://jira.sw.ru/browse/PSBM-125095
> (cherry picked from commit e3336cab2579012b1e72b5265adf98e2d6e244ad)
> Signed-off-by: Andrey Ryabinin 
> ---
>  mm/vmscan.c | 8 
>  1 file changed, 8 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 85622f235e78..080500f4e366 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2684,6 +2684,14 @@ static void shrink_zone(struct zone *zone, struct 
> scan_control *sc,
>   do {
>   unsigned long lru_pages, scanned;
>  
> + /*
> +  * This loop can become CPU-bound when target memcgs
> +  * aren't eligible for reclaim - either because they
> +  * don't have any reclaimable pages, or because their
> +  * memory is explicitly protected. Avoid soft lockups.
> +  */
> + cond_resched();
> +
>   if (!sc->may_thrash && mem_cgroup_low(root, memcg))
>   continue;
>  
> 

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