Re: [Lsf-pc] [LSF/MM TOPIC] Improving CMA

[SeongJae Park <sj38.park@gmail.com>]

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Hi Gioh,

On Wed, 26 Nov 2014, Gioh Kim wrote:

>
>
> 2014-11-25 i??i?? 8:32i?? Mel Gorman i?'(e??) i?' e,?:
>> On Mon, Nov 24, 2014 at 05:54:14PM -0800, Laura Abbott wrote:
>>> There have been a number of patch series posted designed to improve 
>>> various
>>> aspects of CMA. A sampling:
>>> 
>>> https://lkml.org/lkml/2014/10/15/623
>>> http://marc.info/?l=linux-mm&m=141571797202006&w=2
>>> https://lkml.org/lkml/2014/6/26/549
>>> 
>>> As far as I can tell, these are all trying to fix real problems with CMA 
>>> but
>>> none of them have moved forward very much from what I can tell. The goal 
>>> of
>>> this session would be to come out with an agreement on what are the 
>>> biggest
>>> problems with CMA and the best ways to solve them.
>>> 
>> 
>> I think this is a good topic. Some of the issues have been brought up 
>> before
>> at LSF/MM but they never made that much traction so it's worth revisiting. 
>> I
>> haven't been paying close attention to the mailing list discussions but
>> I've been a little worried that the page allocator paths are turning into
>> a bigger and bigger mess. I'm also a bit worried that options such as
>> migrating pages out of CMA areas that are about to be pinned for having
>> callback options to forcibly free pages never went anywhere.
>> 
>
>
> I have two question.
>
> First, is GCMA able to replace CMA? It's news to me.

Yes, it can. GCMA could replace or co-exist and be used selectively with 
CMA. You could replace CMA with GCMA by simply changing 
cma_declare_contiguous() function call with gcma_declare_contiguous().

> I need some time to check GCMA.

1st RFC of GCMA was posted on linux-mm mailing list as Laura linked and 
you could get whole code from gcma/rfc/v1 tag of 
https://github.com/sjp38/linux.gcma. It would great for me if you could 
check it and give me any feedback because GCMA have lots of TODO / Future 
plans and 2nd RFC is acively developing already.

Thanks,
SeongJae Park

>
> Second, is CMA popular enough to change allocator path?
> Yes, I need it.
> But I don't know any company uses it, and nobody seems to have interest in 
> it.
>