APPLIED: [X/B][PATCH] mm: do not stall register_shrinker()

[Khaled Elmously]

On 2019-02-25 19:26:11 , Mauricio Faria de Oliveira wrote:
> From: Minchan Kim <minchan at kernel.org>
> 
> BugLink: https://bugs.launchpad.net/bugs/1817628
> 
> Shakeel Butt reported he has observed in production systems that the job
> loader gets stuck for 10s of seconds while doing a mount operation.  It
> turns out that it was stuck in register_shrinker() because some
> unrelated job was under memory pressure and was spending time in
> shrink_slab().  Machines have a lot of shrinkers registered and jobs
> under memory pressure have to traverse all of those memcg-aware
> shrinkers and affect unrelated jobs which want to register their own
> shrinkers.
> 
> To solve the issue, this patch simply bails out slab shrinking if it is
> found that someone wants to register a shrinker in parallel.  A downside
> is it could cause unfair shrinking between shrinkers.  However, it
> should be rare and we can add compilcated logic if we find it's not
> enough.
> 
> [akpm at linux-foundation.org: tweak code comment]
> Link: http://lkml.kernel.org/r/20171115005602.GB23810@bbox
> Link: http://lkml.kernel.org/r/1511481899-20335-1-git-send-email-minchan@kernel.org
> Signed-off-by: Minchan Kim <minchan at kernel.org>
> Signed-off-by: Shakeel Butt <shakeelb at google.com>
> Reported-by: Shakeel Butt <shakeelb at google.com>
> Tested-by: Shakeel Butt <shakeelb at google.com>
> Acked-by: Johannes Weiner <hannes at cmpxchg.org>
> Acked-by: Michal Hocko <mhocko at suse.com>
> Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
> Cc: Anshuman Khandual <khandual at linux.vnet.ibm.com>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> (backported from commit e496612c5130567fc9d5f1969ca4b86665aa3cbb)
> [mfo: refresh one context line for do_shrink_slab() arguments]
> Signed-off-by: Mauricio Faria de Oliveira <mfo at canonical.com>
> ---
>  mm/vmscan.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f53dcdccdb83..decc5f99b85c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -453,6 +453,15 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
>  			sc.nid = 0;
>  
>  		freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
> +		/*
> +		 * Bail out if someone want to register a new shrinker to
> +		 * prevent the regsitration from being stalled for long periods
> +		 * by parallel ongoing shrinking.
> +		 */
> +		if (rwsem_is_contended(&shrinker_rwsem)) {
> +			freed = freed ? : 1;
> +			break;
> +		}
>  	}
>  
>  	up_read(&shrinker_rwsem);
> -- 
> 2.17.1
> 
> 
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