linux-kernel - Re: [PATCH] mm: vmscan: avoid a unnecessary reschedule in shrink

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Message-ID: <20201016120749.GG22589@dhcp22.suse.cz>
Date:   Fri, 16 Oct 2020 14:07:49 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Xianting Tian <tian.xianting@....com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: vmscan: avoid a unnecessary reschedule in
 shrink_slab()

On Fri 16-10-20 11:39:52, Xianting Tian wrote:
> In shrink_slab(), it directly goes to 'out' label only when it
> can't get the lock of shrinker_rwsew. In this case, it doesn't
> do the real work of shrinking slab, so we don't need trigger a
> reschedule by cond_resched().

Your changelog doesn't explain why this is not needed or undesirable. Do
you see any actual problem?

The point of this code is to provide a deterministic scheduling point
regardless of the shrinker_rwsew.

> 
> Signed-off-by: Xianting Tian <tian.xianting@....com>
> ---
>  mm/vmscan.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 466fc3144..676e97b28 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -687,8 +687,9 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
>  	}
>  
>  	up_read(&shrinker_rwsem);
> -out:
> +
>  	cond_resched();
> +out:
>  	return freed;
>  }
>  
> -- 
> 2.17.1
> 

-- 
Michal Hocko
SUSE Labs