linux-kernel - Re: [PATCH 3/3] mm: page allocator: Reconsider zones for allocation after direct reclaim

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Message-ID: <4E1CE9FF.3050707@jp.fujitsu.com>
Date:	Wed, 13 Jul 2011 09:42:39 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	mgorman@...e.de
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm: page allocator: Reconsider zones for allocation
 after direct reclaim

(2011/07/11 22:01), Mel Gorman wrote:
> With zone_reclaim_mode enabled, it's possible for zones to be considered
> full in the zonelist_cache so they are skipped in the future. If the
> process enters direct reclaim, the ZLC may still consider zones to be
> full even after reclaiming pages. Reconsider all zones for allocation
> if direct reclaim returns successfully.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Hmmm...

I like the concept, but I'm worry about a corner case a bit.

If users are using cpusets/mempolicy, direct reclaim don't scan all zones.
Then, zlc_clear_zones_full() seems too aggressive operation.
Instead, couldn't we turn zlc->fullzones off from kswapd?


> ---
>  mm/page_alloc.c |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6913854..149409c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1616,6 +1616,21 @@ static void zlc_mark_zone_full(struct zonelist *zonelist, struct zoneref *z)
>  	set_bit(i, zlc->fullzones);
>  }
>  
> +/*
> + * clear all zones full, called after direct reclaim makes progress so that
> + * a zone that was recently full is not skipped over for up to a second
> + */
> +static void zlc_clear_zones_full(struct zonelist *zonelist)
> +{
> +	struct zonelist_cache *zlc;	/* cached zonelist speedup info */
> +
> +	zlc = zonelist->zlcache_ptr;
> +	if (!zlc)
> +		return;
> +
> +	bitmap_zero(zlc->fullzones, MAX_ZONES_PER_ZONELIST);
> +}
> +
>  #else	/* CONFIG_NUMA */
>  
>  static nodemask_t *zlc_setup(struct zonelist *zonelist, int alloc_flags)
> @@ -1963,6 +1978,10 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
>  	if (unlikely(!(*did_some_progress)))
>  		return NULL;
>  
> +	/* After successful reclaim, reconsider all zones for allocation */
> +	if (NUMA_BUILD)
> +		zlc_clear_zones_full(zonelist);
> +
>  retry:
>  	page = get_page_from_freelist(gfp_mask, nodemask, order,
>  					zonelist, high_zoneidx,


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