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

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Date:	Thu, 16 Oct 2014 13:13:57 +0800
From:	Weijie Yang <weijie.yang.kh@...il.com>
To:	Hui Zhu <zhuhui@...omi.com>
Cc:	rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
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Subject: Re: [PATCH 0/4] (CMA_AGGRESSIVE) Make CMA memory be more aggressive
 about allocation

On Thu, Oct 16, 2014 at 11:35 AM, Hui Zhu <zhuhui@...omi.com> 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.

I'm not very clear to this description, what issue do you try to solve?
Make MIGRATE_CMA be the fallback of desired MIGRATE_UNMOVABLE?

> 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.

I don't think so. That will cause MIGRATE_CMA depleted prematurely, and when a
user(such as camera) wants CMA memory, he will not get the wanted memory.

> Then the memory of MIGRATE_MOVABLE can be kept for MIGRATE_UNMOVABLE and
> MIGRATE_RECLAIMABLE which doesn't have fallback MIGRATE_CMA.

I don't think this is the root cause of oom.
But I am interested in the CMA shrinker idea, I will follow this mail.

Thanks for your work, add some test data will be better.

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