linux-kernel - Re: TTM page pool allocator

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Date:	Wed, 22 Jul 2009 10:27:00 +0200
From:	Thomas Hellström <thomas@...pmail.org>
To:	Jerome Glisse <glisse@...edesktop.org>
CC:	Dave Airlie <airlied@...il.com>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.sf.net
Subject: Re: TTM page pool allocator

Jerome Glisse wrote:
> On Thu, 2009-06-25 at 17:53 +0200, Thomas Hellström wrote:
>   
>> Jerome Glisse skrev:
>>     
>>> Hi,
>>>
>>> Thomas i attach a reworked page pool allocator based on Dave works,
>>> this one should be ok with ttm cache status tracking. It definitely
>>> helps on AGP system, now the bottleneck is in mesa vertex's dma
>>> allocation.
>>>
>>> Cheers,
>>> Jerome
>>>   
>>>       
>> Hi, Jerome!
>> In general it looks very good. Some things that need fixing:
>>
>> 1)  We must have a way to hand back pages. I still not quite understand 
>> how the shrink callbacks work and whether they are applicable. Another 
>> scheme would be to free, say 1MB when we have at least 2MB available.
>>
>> 2) We should avoid including AGP headers if AGP is not configured. 
>> Either reimplement unmap_page_from_agp or map_page_into_agp or move them 
>> out from the AGP headers. We've hade complaints before from people with 
>> AGP free systems that the code doesn't compile.
>>
>> 3) Since we're allocating (and freeing) in batches we should use the 
>> set_pages_array() interface to avoid a global tlb flush per page.
>>
>> 4) We could now skip the ttm_tt_populate() in ttm_tt_set_caching, since 
>> it will always allocate cached pages and then transition them.
>>
>>     
>
> Okay 4) is bad, what happens (my brain is a bit meltdown so i might be
> wrong) :
> 1 - bo get allocated tt->state = unpopulated
> 2 - bo is mapped few page are faulted tt->state = unpopulated
> 3 - bo is cache transitioned but tt->state == unpopulated but
>     they are page which have been touch by the cpu so we need
>     to clflush them and transition them, 

Right.

> this never happen if
>     we don't call ttm_tt_populate and proceed with the remaining
>     of the cache transitioning functions
>   

Why can't we just skip ttm_tt_populate and proceed with the remaining of 
the cache transitioning functions? Then all pages currently allocated to 
the TTM will be transitioned.

/Thomas



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