linux-kernel - Re: [PATCH 31/35] Optimistically check the first page on the PCP free list is suitable

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Message-ID: <alpine.DEB.1.10.0903161232130.32577@qirst.com>
Date:	Mon, 16 Mar 2009 12:33:44 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 31/35] Optimistically check the first page on the PCP
 free list is suitable

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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