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

[Kirill Tkhai]

On 01.02.2021 17:10, Andrey Ryabinin wrote:
> From: Xunlei Pang <xlpang at linux.alibaba.com>
> 
> 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 <mhocko at suse.com>
> Signed-off-by: Xunlei Pang <xlpang at linux.alibaba.com>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Acked-by: Chris Down <chris at chrisdown.name>
> Acked-by: Michal Hocko <mhocko at suse.com>
> Acked-by: Johannes Weiner <hannes at cmpxchg.org>
> Link: http://lkml.kernel.org/r/1598495549-67324-1-git-send-email-xlpang@linux.alibaba.com
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>

> 
> https://jira.sw.ru/browse/PSBM-125095
> (cherry picked from commit e3336cab2579012b1e72b5265adf98e2d6e244ad)
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
> ---
>  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;
>  
>