linux-kernel - Re: Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer

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Date:	Fri, 3 Oct 2008 00:25:44 +0900 (JST)
From:	kamezawa.hiroyu@...fujitsu.com
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer

----- Original Message -----

>On Thu, Oct 02, 2008 at 04:24:14PM +0900, KAMEZAWA Hiroyuki wrote:
>> On Wed,  1 Oct 2008 13:31:01 +0100
>> Andy Whitcroft <apw@...dowen.org> wrote:
>> 
>> > When a process enters direct reclaim it will expend effort identifying
>> > and releasing pages in the hope of obtaining a page.  However as these
>> > pages are released asynchronously there is every possibility that the
>> > pages will have been consumed by other allocators before the reclaimer
>> > gets a look in.  This is particularly problematic where the reclaimer is
>> > attempting to allocate a higher order page.  It is highly likely that
>> > a parallel allocation will consume lower order constituent pages as we
>> > release them preventing them coelescing into the higher order page the
>> > reclaimer desires.
>> > 
>> > This patch set attempts to address this for allocations above
>> > ALLOC_COSTLY_ORDER by temporarily collecting the pages we are releasing
>> > onto a local free list.  Instead of freeing them to the main buddy lists,
>> > pages are collected and coelesced on this per direct reclaimer free list.
>> > Pages which are freed by other processes are also considered, where they
>> > coelesce with a page already under capture they will be moved to the
>> > capture list.  When pressure has been applied to a zone we then consult
>> > the capture list and if there is an appropriatly sized page available
>> > it is taken immediatly and the remainder returned to the free pool.
>> > Capture is only enabled when the reclaimer's allocation order exceeds
>> > ALLOC_COSTLY_ORDER as free pages below this order should naturally occur
>> > in large numbers following regular reclaim.
>> > 
>> > Thanks go to Mel Gorman for numerous discussions during the development
>> > of this patch and for his repeated reviews.
>> > 
>> 
>> Hmm.. is this routine better than
>>   mm/memory_hotplug.c::do_migrate_range(start_pfn, end_pfn) ?
>
>Are you suggesting that it might be more adventageous to try and migrate
>things out of this area as part of reclaim?  If so then I tend to agree,
>though that would be a good idea generally with or without capture.
>
>/me adds it to his todo list to test that out.
>
I just remember I did the same kind of work to offline pages.
Sorry for noise.

I just have an idea to support following kind of interface via memory hotplug
This makes all pages in the section to be hugepage.

 #echo huge > /sys/device/system/memory/memoryXXX/state
 (memory hotplug interface supports online/offline here.)

But no patches yet...

Thanks,
-Kame


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