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

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Date:   Thu, 22 Sep 2016 14:32:18 +0900
From:   Joonsoo Kim <iamjoonsoo.kim@....com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.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

On Wed, Sep 21, 2016 at 08:17:27PM +0530, Aneesh Kumar K.V wrote:
> "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.

Yep! I will take a look on those problems after merging this patchset.

> 
> You can add for the complete series.
> 
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

Thanks!