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

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Hi Gioh,

On Wed, 26 Nov 2014, Gioh Kim wrote:



2014-11-25 오후 8:32에 Mel Gorman 이(가) 쓴 글:
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.

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