Re: [PATCH 0/4] (CMA_AGGRESSIVE) Make CMA memory be more aggressive about allocation

[Hui Zhu]

On Wed, Oct 29, 2014 at 10:43 PM, Vlastimil Babka <vbabka@xxxxxxx> wrote:
> On 10/16/2014 10:55 AM, Laura Abbott wrote:
>>
>> On 10/15/2014 8:35 PM, Hui Zhu wrote:
>>
>> It's good to see another proposal to fix CMA utilization. Do you have
>> any data about the success rate of CMA contiguous allocation after
>> this patch series? I played around with a similar approach of using
>> CMA for MIGRATE_MOVABLE allocations and found that although utilization
>> did increase, contiguous allocations failed at a higher rate and were
>> much slower. I see what this series is trying to do with avoiding
>> allocation from CMA pages when a contiguous allocation is progress.
>> My concern is that there would still be problems with contiguous
>> allocation after all the MIGRATE_MOVABLE fallback has happened.
>
>
> Hi,
>
> did anyone try/suggest the following idea?
>
> - keep CMA as fallback to MOVABLE as is is now, i.e. non-agressive
> - when UNMOVABLE (RECLAIMABLE also?) allocation fails and CMA pageblocks
> have space, don't OOM immediately, but first try to migrate some MOVABLE
> pages to CMA pageblocks, to make space for the UNMOVABLE allocation in
> non-CMA pageblocks
> - this should keep CMA pageblocks free as long as possible and useful for
> CMA allocations, but without restricting the non-MOVABLE allocations even
> though there is free memory (but in CMA pageblocks)
> - the fact that a MOVABLE page could be successfully migrated to CMA
> pageblock, means it was not pinned or otherwise non-migratable, so there's a
> good chance it can be migrated back again if CMA pageblocks need to be used
> by CMA allocation
> - it's more complex, but I guess we have most of the necessary
> infrastructure in compaction already :)

I think this idea make CMA allocation part become complex but make
balance and shrink code become easy because it make CMA become real
memory.
I just worry about the speed of migrate memory with this idea.  :)

Thanks,
Hui


>
> Thoughts?
> Vlastimil
>
>> Thanks,
>> Laura
>>
>
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