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 01:55:46 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Hui Zhu <zhuhui@...omi.com>, rjw@...ysocki.net,
	len.brown@...el.com, pavel@....cz, m.szyprowski@...sung.com,
	akpm@...ux-foundation.org, mina86@...a86.com,
	aneesh.kumar@...ux.vnet.ibm.com, iamjoonsoo.kim@....com,
	hannes@...xchg.org, riel@...hat.com, mgorman@...e.de,
	minchan@...nel.org, nasa4836@...il.com, ddstreet@...e.org,
	hughd@...gle.com, mingo@...nel.org, rientjes@...gle.com,
	peterz@...radead.org, keescook@...omium.org, atomlin@...hat.com,
	raistlin@...ux.it, axboe@...com, paulmck@...ux.vnet.ibm.com,
	kirill.shutemov@...ux.intel.com, n-horiguchi@...jp.nec.com,
	k.khlebnikov@...sung.com, msalter@...hat.com, deller@....de,
	tangchen@...fujitsu.com, ben@...adent.org.uk,
	akinobu.mita@...il.com, vbabka@...e.cz, sasha.levin@...cle.com,
	vdavydov@...allels.com, suleiman@...gle.com
CC:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 0/4] (CMA_AGGRESSIVE) Make CMA memory be more aggressive
 about allocation

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.

Thanks,
Laura

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