linux-kernel - Re: [patch 1/2] mm, page_alloc: extend kernelcore and movablecore for percent

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Message-ID: <20180214095911.GB28460@dhcp22.suse.cz>
Date:   Wed, 14 Feb 2018 10:59:11 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org
Subject: Re: [patch 1/2] mm, page_alloc: extend kernelcore and movablecore
 for percent

On Mon 12-02-18 16:24:25, David Rientjes wrote:
> Both kernelcore= and movablecore= can be used to define the amount of
> ZONE_NORMAL and ZONE_MOVABLE on a system, respectively.  This requires
> the system memory capacity to be known when specifying the command line,
> however.
> 
> This introduces the ability to define both kernelcore= and movablecore=
> as a percentage of total system memory.  This is convenient for systems
> software that wants to define the amount of ZONE_MOVABLE, for example, as
> a proportion of a system's memory rather than a hardcoded byte value.
> 
> To define the percentage, the final character of the parameter should be
> a '%'.

I do not have any objections regarding the extension. What I am more
interested in is _why_ people are still using this command line
parameter at all these days. Why would anybody want to introduce lowmem
issues from 32b days. I can see the CMA/Hotplug usecases for
ZONE_MOVABLE but those have their own ways to define zone movable. I was
tempted to simply remove the kernelcore already. Could you be more
specific what is your usecase which triggered a need of an easier
scaling of the size?
-- 
Michal Hocko
SUSE Labs