linux-kernel - Re: [PATCH v7 0/7] Introduce ZONE

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Message-ID: <20170411181519.GC21171@dhcp22.suse.cz>
Date:   Tue, 11 Apr 2017 20:15:20 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     js1304@...il.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        mgorman@...hsingularity.net, Laura Abbott <lauraa@...eaurora.org>,
        Minchan Kim <minchan@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v7 0/7] Introduce ZONE_CMA

Hi,
I didn't get to read though patches yet but the cover letter didn't
really help me to understand the basic concepts to have a good starting
point before diving into implementation details. It contains a lot of
history remarks which is not bad but IMHO too excessive here. I would
appreciate the following information (some of that is already provided
in the cover but could benefit from some rewording/text reorganization).

- what is ZONE_CMA and how it is configured (from admin POV)
- how does ZONE_CMA compare to other zones
- who is allowed to allocate from this zone and what are the
  guarantees/requirements for successful allocation
- how does the zone compare to a preallocate allocation pool
- how is ZONE_CMA balanced/reclaimed due to internal memory pressure
  (from CMA users)
- is this zone reclaimable for the global memory reclaim
- why this was/is controversial
-- 
Michal Hocko
SUSE Labs