Re: [LSF/MM TOPIC] Improving CMA

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

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 also tried to solve problem from CMA, that is, reserved memory
utilization.

https://lkml.org/lkml/2014/5/28/64

While playing that patchset, I found serious problem about free page
counting, so I stopped to develop it for a while and tried to fix it.
Now, it is fixed by me and I can continue my patchset.

https://lkml.org/lkml/2014/10/31/69

I heard that Minchan suggests new CMA zone like movable zone, and, I
think that it would be the way to go. But, it would be a long-term goal
and I'd like to solve utilization problem with my patchset for now.
It is the biggest issue and it already forces someone to develop
out of tree solution. It's not good that out of tree solution is used
more and more in the product so I'd like to fix it quickly at first
stage.

I think that CMA have big potential. If we fix problems of CMA
completely, it can be used for many places. One such case in my mind
is hugetlb or THP. Until now, hugetlb uses reserved approach, that is
very inefficient. System administrator carefully set the number of
reserved hugepage according to whole system workload. And application
can't use it freely, because it is very limited and managed resource.
If we use CMA for hugetlb, we can easily allocate hugepage and
application can use hugepages more freely.

Anyway, I'd like to attend LSF/MM and discuss this topic.

Thanks.

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