linux-kernel - Re: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it

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Date:	Wed, 04 Nov 2009 08:12:18 +1100
From:	Nigel Cunningham <ncunningham@...a.org.au>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic
 and unify it

Hi Rafael.

Rafael J. Wysocki wrote:
> On Monday 02 November 2009, Nigel Cunningham wrote:
>> Hi.
> 
> Hi,
> 
>> KOSAKI Motohiro wrote:
>>>> I haven't given much thought to numa awareness in hibernate code, but I
>>>> can say that the shrink_all_memory interface is woefully inadequate as
>>>> far as zone awareness goes. Since lowmem needs to be atomically restored
>>>> before we can restore highmem, we really need to be able to ask for a
>>>> particular number of pages of a particular zone type to be freed.
>>> Honestly, I am not suspend/hibernation expert. Can I ask why caller need to know
>>> per-zone number of freed pages information? if hibernation don't need highmem.
>>> following incremental patch prevent highmem reclaim perfectly. Is it enough?
>> (Disclaimer: I don't think about highmem a lot any more, and might have
>> forgotten some of the details, or swsusp's algorithms might have
>> changed. Rafael might need to correct some of this...)
>>
>> Imagine that you have a system with 1000 pages of lowmem and 5000 pages
>> of highmem. Of these, 950 lowmem pages are in use and 500 highmem pages
>> are in use.
>>
>> In order to to be able to save an image, we need to be able to do an
>> atomic copy of those lowmem pages.
>>
>> You might think that we could just copy everything into the spare
>> highmem pages, but we can't because mapping and unmapping the highmem
>> pages as we copy the data will leave us with an inconsistent copy.
> 
> This isn't the case any more for the mainline hibernate code.  We use highmem
> for storing image data as well as lowmem.

Highmem for storing copies of lowmem pages?

Regards,

Nigel
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