linux-kernel - Re: [PATCH] fix page_alloc for larger I/O segments

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Date:	Thu, 13 Dec 2007 17:03:08 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mark Lord <liml@....ca>
Cc:	James.Bottomley@...senPartnership.com, jens.axboe@...cle.com,
	lkml@....ca, matthew@....cx, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-mm@...ck.org, mel@....ul.ie
Subject: Re: [PATCH] fix page_alloc for larger I/O segments

On Thu, 13 Dec 2007 19:40:09 -0500
Mark Lord <liml@....ca> wrote:

> And here is a patch that seems to fix it for me here:
> 
> * * * *
> 
> Fix page allocator to give better change of larger contiguous segments (again).
> 
> Signed-off-by: Mark Lord <mlord@...ox.com
> ---
> 
> 
> --- old/mm/page_alloc.c.orig	2007-12-13 19:25:15.000000000 -0500
> +++ linux-2.6/mm/page_alloc.c	2007-12-13 19:35:50.000000000 -0500
> @@ -954,7 +954,7 @@
>  				goto failed;
>  		}
>  		/* Find a page of the appropriate migrate type */
> -		list_for_each_entry(page, &pcp->list, lru) {
> +		list_for_each_entry_reverse(page, &pcp->list, lru) {
>  			if (page_private(page) == migratetype) {
>  				list_del(&page->lru);
>  				pcp->count--;

- needs help to make it apply to mainline

- needs a comment, methinks...


--- a/mm/page_alloc.c~fix-page-allocator-to-give-better-chance-of-larger-contiguous-segments-again
+++ a/mm/page_alloc.c
@@ -1060,8 +1060,12 @@ again:
 				goto failed;
 		}
 
-		/* Find a page of the appropriate migrate type */
-		list_for_each_entry(page, &pcp->list, lru)
+		/*
+		 * Find a page of the appropriate migrate type.  Doing a
+		 * reverse-order search here helps us to hand out pages in
+		 * ascending physical-address order.
+		 */
+		list_for_each_entry_reverse(page, &pcp->list, lru)
 			if (page_private(page) == migratetype)
 				break;
 
_

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