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

["Thomas Hellström" <thomas@tungstengraphics.com>]

Keith Packard wrote:
> On Thu, 2008-09-25 at 00:19 -0700, Thomas HellstrA?m 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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