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Date: Wed, 17 May 2017 16:44:26 +0900
From: Joonsoo Kim <js1304@gmail.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
        mgorman@techsingularity.net, Laura Abbott <lauraa@codeaurora.org>,
        Minchan Kim <minchan@kernel.org>,
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        Michal Nazarewicz <mina86@mina86.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>, Russell King <linux@armlinux.org.uk>,
        Will Deacon <will.deacon@arm.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@lge.com
Subject: Re: [PATCH v7 0/7] Introduce ZONE_CMA
Message-ID: <20170517074424.GC18406@js1304-desktop>
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> > 
> > Okay. We did a lot of discussion so it's better to summarise it.
> > 
> > 1. ZONE_CMA might be a nicer solution than MIGRATETYPE.
> > 2. Additional bit in page flags would cause another kind of
> > maintenance problem so it's better to avoid it as much as possible.
> > 3. Abusing ZONE_MOVABLE looks better than introducing ZONE_CMA since
> > it doesn't need additional bit in page flag.
> > 4. (Not-yet-finished) If ZONE_CMA doesn't need extra bit in page
> > flags with hacky magic and it has no performance regression,
> > ??? (it's okay to use separate zone for CMA?)
> 
> As mentioned above. I do not see why we should go over additional hops
> just to have a zone which is not strictly needed. So if there are no
> inherent problems reusing MOVABLE/HIGMEM zone then a separate zone
> sounds like a wrong direction.
> 
> But let me repeat. I am _not_ convinced that the migratetype situation
> is all that bad and unfixable. You have mentioned some issues with the
> current approach but none of them seem inherently unfixable. So I would
> still prefer keeping the current way. But I am not going to insist if
> you _really_ believe that the long term maintenance cost will be higher
> than a zone approach and you can reuse MOVABLE/HIGHMEM zones without
> disruptive changes. I can help you with the hotplug part of the MOVABLE
> zone because that is desirable on its own.

Okay. Thanks for sharing your opinion. I will decide the final
direction after some investigation.

Thanks.