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

[Hui Zhu]

On Fri, Oct 24, 2014 at 1:25 PM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
> On Thu, Oct 16, 2014 at 11:35:47AM +0800, 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.
>
> Hello,
>
> I did some work similar to this.
> Please reference following links.
>
> https://lkml.org/lkml/2014/5/28/64
> https://lkml.org/lkml/2014/5/28/57

> I tested #1 approach and found the problem. Although free memory on
> meminfo can move around low watermark, there is large fluctuation on free
> memory, because too many pages are reclaimed when kswapd is invoked.
> Reason for this behaviour is that successive allocated CMA pages are
> on the LRU list in that order and kswapd reclaim them in same order.
> These memory doesn't help watermark checking from kwapd, so too many
> pages are reclaimed, I guess.

This issue can be handle with some change around shrink code.  I am
trying to integrate  a patch for them.
But I am not sure we met the same issue.  Do you mind give me more
info about this part?

>
> And, aggressive allocation should be postponed until freepage counting
> bug is fixed, because aggressive allocation enlarge the possiblity
> of problem occurence. I tried to fix that bug, too. See following link.
>
> https://lkml.org/lkml/2014/10/23/90

I am following these patches.  They are great!  Thanks for your work.

Best,
Hui

>
> Thanks.
>
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