linux-kernel - Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct reclaim allocation fails

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Date:	Thu, 9 Sep 2010 08:45:16 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mel@....ul.ie>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct
 reclaim allocation fails

On Thu, 9 Sep 2010, Mel Gorman wrote:

> @@ -1876,10 +1890,13 @@ retry:
>  					migratetype);
>
>  	/*
> -	 * If an allocation failed after direct reclaim, it could be because
> -	 * pages are pinned on the per-cpu lists. Drain them and try again
> +	 * If a high-order allocation failed after direct reclaim, it could
> +	 * be because pages are pinned on the per-cpu lists. However, only
> +	 * do it for PAGE_ALLOC_COSTLY_ORDER as the cost of the IPI needed
> +	 * to drain the pages is itself high. Assume that lower orders
> +	 * will naturally free without draining.
>  	 */
> -	if (!page && !drained) {
> +	if (!page && !drained && order > PAGE_ALLOC_COSTLY_ORDER) {
>  		drain_all_pages();
>  		drained = true;
>  		goto retry;
>

This will have the effect of never sending IPIs for slab allocations since
they do not do allocations for orders > PAGE_ALLOC_COSTLY_ORDER.

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