Message-ID: <543F8812.2020002@codeaurora.org>
Date: Thu, 16 Oct 2014 01:55:46 -0700
From: Laura Abbott <lauraa@codeaurora.org>
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To: Hui Zhu <zhuhui@xiaomi.com>, rjw@rjwysocki.net, len.brown@intel.com,
        pavel@ucw.cz, m.szyprowski@samsung.com, akpm@linux-foundation.org,
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CC: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 0/4] (CMA_AGGRESSIVE) Make CMA memory be more aggressive
 about allocation
References: <1413430551-22392-1-git-send-email-zhuhui@xiaomi.com>
In-Reply-To: <1413430551-22392-1-git-send-email-zhuhui@xiaomi.com>
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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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