linux-kernel - Re: [PATCH v5 0/6] Introduce ZONE

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Message-Id: <87eg4dwbr4.fsf@linux.vnet.ibm.com>
Date:   Wed, 21 Sep 2016 20:17:27 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Laura Abbott <lauraa@...eaurora.org>,
        Minchan Kim <minchan@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 0/6] Introduce ZONE_CMA

"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:

> Joonsoo Kim <iamjoonsoo.kim@....com> writes:
>
>> On Tue, Aug 30, 2016 at 04:09:37PM +0530, Aneesh Kumar K.V wrote:
>>> Joonsoo Kim <js1304@...il.com> writes:
>>> 
>>> > 2016-08-29 18:27 GMT+09:00 Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>:
>>> >> js1304@...il.com writes:
>>> >>
>>> >>> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>>> >>>
>>> >>> Hello,
>>> >>>
>>> >>> Changes from v4
>>> >>> o Rebase on next-20160825
>>> >>> o Add general fix patch for lowmem reserve
>>> >>> o Fix lowmem reserve ratio
>>> >>> o Fix zone span optimizaion per Vlastimil
>>> >>> o Fix pageset initialization
>>> >>> o Change invocation timing on cma_init_reserved_areas()
>>> >>
>>> >> I don't see much information regarding how we interleave between
>>> >> ZONE_CMA and other zones for movable allocation. Is that explained in
>>> >> any of the patch ? The fair zone allocator got removed by
>>> >> e6cbd7f2efb433d717af72aa8510a9db6f7a7e05
>>> >
>>> > Interleaving would not work since the fair zone allocator policy is removed.
>>> > I don't think that it's a big problem because it is just matter of
>>> > timing to fill
>>> > up the memory. Eventually, memory on ZONE_CMA will be fully used in
>>> > any case.
>>> 
>>> Does that mean a CMA allocation will now be slower because in most case we
>>> will need to reclaim ? The zone list will now have ZONE_CMA in the
>>> beginning right ?
>>
>> ZONE_CMA will be used first but I don't think that CMA allocation will
>> be slower. In most case, memory would be fully used (usually
>> by page cache). So, we need reclaim or migration in any case.
>
> Considering that the upstream kernel doesn't allow migration of THP
> pages, this would mean that migrate will fail in most case if we have
> THP enabled and the THP allocation request got satisfied via ZONE_CMA.
> Isn't that going to be a problem ?
>

Even though we have the issues of migration failures due to pinned and
THP pages in ZONE_CMA, overall the code is simpler. IMHO we should get
this upstream now and work on solving those issues later.

You can add for the complete series.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

-aneesh