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Date: Mon, 16 Mar 2009 12:33:44 -0400 (EDT)
From: Christoph Lameter <cl@linux-foundation.org>
Subject: Re: [PATCH 31/35] Optimistically check the first page on the PCP
 free list is suitable
In-Reply-To: <1237196790-7268-32-git-send-email-mel@csn.ul.ie>
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References: <1237196790-7268-1-git-send-email-mel@csn.ul.ie> <1237196790-7268-32-git-send-email-mel@csn.ul.ie>
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Sender: owner-linux-mm@kvack.org
To: Mel Gorman <mel@csn.ul.ie>
Cc: Linux Memory Management List <linux-mm@kvack.org>, Pekka Enberg <penberg@cs.helsinki.fi>, Rik van Riel <riel@redhat.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Johannes Weiner <hannes@cmpxchg.org>, Nick Piggin <npiggin@suse.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Lin Ming <ming.m.lin@intel.com>, Zhang Yanmin <yanmin_zhang@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>
List-ID: <linux-mm.kvack.org>

On Mon, 16 Mar 2009, Mel Gorman wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bb5bd5e..8568284 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1212,6 +1212,12 @@ again:
>  				if (pcp_page_suit(page, order))
>  					break;
>  		} else {
> +			/* Optimistic before we start a list search */
> +			page = list_entry(list->next, struct page, lru);
> +			if (pcp_page_suit(page, order))
> +				goto found;
> +
> +			/* Do the search */
>  			list_for_each_entry(page, list, lru)
>  				if (pcp_page_suit(page, order))
>  					break;

I am not convinced that this is beneficial. If it would then the compiler
would unroll the loop.


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