linux-kernel - Re: [patch] mm: pageable memory allocator (for DRM-GEM?)

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Message-ID: <48DBB0B3.2010500@tungstengraphics.com>
Date:	Thu, 25 Sep 2008 17:39:31 +0200
From:	Thomas Hellström <thomas@...gstengraphics.com>
To:	Keith Packard <keithp@...thp.com>
CC:	Nick Piggin <npiggin@...e.de>, "eric@...olt.net" <eric@...olt.net>,
	"hugh@...itas.com" <hugh@...itas.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"airlied@...ux.ie" <airlied@...ux.ie>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"dri-devel@...ts.sourceforge.net" <dri-devel@...ts.sourceforge.net>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch] mm: pageable memory allocator (for DRM-GEM?)

Keith Packard wrote:
> On Thu, 2008-09-25 at 00:19 -0700, Thomas Hellström wrote:
>   
>>  If data is
>> dirtied in VRAM or the page(s) got discarded
>>  we need new pages and to set up a copy operation.
>>     
>
> Note that this can occur as a result of a suspend-to-memory transition
> at which point *all* of the objects in VRAM will need to be preserved in
> main memory, and so the pages aren't really 'freed', they just don't
> need to have valid contents, but the system should be aware that the
> space may be needed at some point in the future.
>
>   
Actually, I think the pages must be allowed to be freed, and that we 
don't put a requirement on "pageable"  to keep
swap-space slots for these pages. If we hit an OOM-condition during 
suspend-to-memory that's bad, but let's say we
required "pageable" to keep swap space slots for us, the result would 
perhaps be that another device wasn't able to suspend, or a user-space 
program was killed due to lack of swap-space prior to suspend.

I'm not really sure what's the worst situation, but my feeling is that 
we should not require swap-space to be reserved for VRAM, and abort the 
suspend operation if we hit OOM. That would, in the worst case, mean 
that people with non-UMA laptops and a too small swap partition would 
see their battery run out much quicker than they expected...

/Thomas



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