linux-kernel - Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?

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Message-ID: <47628BC0.7020506@rtr.ca>
Date:	Fri, 14 Dec 2007 08:57:20 -0500
From:	Mark Lord <liml@....ca>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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
Subject: Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?

Mel Gorman wrote:
> On (13/12/07 16:37), Andrew Morton didst pronounce:
>> On Thu, 13 Dec 2007 19:30:00 -0500
>> Mark Lord <liml@....ca> wrote:
>>
>>> Here's the commit that causes the regression:
>>>
>>> ...
>>>
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -760,7 +760,8 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
>>>  		struct page *page = __rmqueue(zone, order, migratetype);
>>>  		if (unlikely(page == NULL))
>>>  			break;
>>> -		list_add_tail(&page->lru, list);
>>> +		list_add(&page->lru, list);
>> well that looks fishy.
>>
> 
> The reasoning behind the change was the first page encountered on the list
> by the caller would have a matching migratetype. I failed to take into
> account the physical ordering of pages returned. I'm setting up to run some
> performance benchmarks of the candidate fix merged into the -mm tree to see
> if the search shows up or not. I'm testing against 2.6.25-rc5 but it'll
> take a few hours to complete.
..

Thanks, Mel.  This is all with CONFIG_SLAB=y, by the way.

Note that it did appear to behave better with CONFIG_SLUB=y when I accidently
used that .config on my 4GB machine here.  Physical segments of 4-10 pages
happended much more common than with CONFIG_SLAB=y on my 3GB machine
Slightly "apples and oranges" there, I know, but at least both were x86-32.  :)

So I would expect CONFIG_SLAB to be well off with this patch under most (all?)
conditions, but dunno about CONFIG_SLUB.

Cheers




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