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

[朱辉 <zhuhui@xiaomi.com>]

On 10/22/14 20:02, Peter Hurley wrote:
> On 10/16/2014 04:55 AM, Laura Abbott wrote:
>> On 10/15/2014 8:35 PM, Hui Zhu wrote:
>>> In fallbacks of page_alloc.c, MIGRATE_CMA is the fallback of
>>> MIGRATE_MOVABLE.
>>> MIGRATE_MOVABLE will use MIGRATE_CMA when it doesn't have a page in
>>> order that Linux kernel want.
>>>
>>> If a system that has a lot of user space program is running, for
>>> instance, an Android board, most of memory is in MIGRATE_MOVABLE and
>>> allocated.  Before function __rmqueue_fallback get memory from
>>> MIGRATE_CMA, the oom_killer will kill a task to release memory when
>>> kernel want get MIGRATE_UNMOVABLE memory because fallbacks of
>>> MIGRATE_UNMOVABLE are MIGRATE_RECLAIMABLE and MIGRATE_MOVABLE.
>>> This status is odd.  The MIGRATE_CMA has a lot free memory but Linux
>>> kernel kill some tasks to release memory.
>>>
>>> This patch series adds a new function CMA_AGGRESSIVE to make CMA memory
>>> be more aggressive about allocation.
>>> If function CMA_AGGRESSIVE is available, when Linux kernel call function
>>> __rmqueue try to get pages from MIGRATE_MOVABLE and conditions allow,
>>> MIGRATE_CMA will be allocated as MIGRATE_MOVABLE first.  If MIGRATE_CMA
>>> doesn't have enough pages for allocation, go back to allocate memory from
>>> MIGRATE_MOVABLE.
>>> Then the memory of MIGRATE_MOVABLE can be kept for MIGRATE_UNMOVABLE and
>>> MIGRATE_RECLAIMABLE which doesn't have fallback MIGRATE_CMA.
>>>
>>
>> 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.
>
> What impact does this series have on x86 platforms now that CMA is the
> backup allocator for all iommu dma allocations?

They will not affect driver CMA memory allocation.

Thanks,
Hui

>
> Regards,
> Peter Hurley
>