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

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Date:	Thu, 13 Dec 2007 17:11:03 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	liml@....ca, 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 (improved)

On Thu, 13 Dec 2007 19:57:29 -0500
James Bottomley <James.Bottomley@...senPartnership.com> wrote:

> 
> On Thu, 2007-12-13 at 19:46 -0500, Mark Lord wrote:
> > "Improved version", more similar to the 2.6.23 code:
> > 
> > Fix page allocator to give better chance of larger contiguous segments (again).
> > 
> > Signed-off-by: Mark Lord <mlord@...ox.com
> > ---
> > 
> > --- old/mm/page_alloc.c	2007-12-13 19:25:15.000000000 -0500
> > +++ linux-2.6/mm/page_alloc.c	2007-12-13 19:43:07.000000000 -0500
> > @@ -760,7 +760,7 @@
> >  		struct page *page = __rmqueue(zone, order, migratetype);
> >  		if (unlikely(page == NULL))
> >  			break;
> > -		list_add(&page->lru, list);
> > +		list_add_tail(&page->lru, list);
> 
> Could we put a big comment above this explaining to the would be vm
> tweakers why this has to be a list_add_tail, so we don't end up back in
> this position after another two years?
> 

Already done ;)

--- a/mm/page_alloc.c~fix-page_alloc-for-larger-i-o-segments-fix
+++ a/mm/page_alloc.c
@@ -847,6 +847,10 @@ static int rmqueue_bulk(struct zone *zon
 		struct page *page = __rmqueue(zone, order, migratetype);
 		if (unlikely(page == NULL))
 			break;
+		/*
+		 * Doing a list_add_tail() here helps us to hand out pages in
+		 * ascending physical-address order.
+		 */
 		list_add_tail(&page->lru, list);
 		set_page_private(page, migratetype);
 	}
_

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