linux-kernel - Re: [Intel-gfx] [PATCH] [RFC] mm/shrinker: Add a shrinker flag to always shrink a bit

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Date:	Wed, 18 Sep 2013 12:38:23 +0200
From:	Knut Petersen <Knut_Petersen@...nline.de>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
CC:	Linux MM <linux-mm@...ck.org>, Rik van Riel <riel@...hat.com>,
	Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	Michal Hocko <mhocko@...e.cz>, Mel Gorman <mgorman@...e.de>,
	Glauber Costa <glommer@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Intel-gfx] [PATCH] [RFC] mm/shrinker: Add a shrinker flag to
 always shrink a bit

On 18.09.2013 11:10, Daniel Vetter wrote:

Just now I prepared a patch changing the same function in vmscan.c
> Also, this needs to be rebased to the new shrinker api in 3.12, I
> simply haven't rolled my trees forward yet.

Well, you should. Since commit 81e49f  shrinker->count_objects might be
set to SHRINK_STOP, causing shrink_slab_node() to complain loud and often:

[ 1908.234595] shrink_slab: i915_gem_inactive_scan+0x0/0x9c negative objects to delete nr=-xxxxxxxxx

The kernel emitted a few thousand log lines like the one quoted above during the
last few days on my system.

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2cff0d4..d81f6e0 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -254,6 +254,10 @@ unsigned long shrink_slab(struct shrink_control *shrink,
>   			total_scan = max_pass;
>   		}
>   
> +		/* Always try to shrink a bit to make forward progress. */
> +		if (shrinker->evicts_to_page_lru)
> +			total_scan = max_t(long, total_scan, batch_size);
> +
At that place the error message is already emitted.
>   		/*
>   		 * We need to avoid excessive windup on filesystem shrinkers
>   		 * due to large numbers of GFP_NOFS allocations causing the

Have a look at the attached patch. It fixes my problem with the erroneous/misleading
error messages, and I think it´s right to just bail out early if SHRINK_STOP is found.

Do you agree ?

cu,
  Knut


View attachment "0001-mm-respect-SHRINK_STOP-in-shrink_slab_node.patch" of type "text/x-patch" (1129 bytes)