linux-kernel - Re: [RFC] calc_memmap_size() isn't accurate and one suggestion to improve

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Message-ID: <20170403091818.GI24661@dhcp22.suse.cz>
Date:   Mon, 3 Apr 2017 11:18:19 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     mgorman@...hsingularity.net, jiang.liu@...ux.intel.com,
        akpm@...ux-foundation.org, tj@...nel.org, mingo@...nel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] calc_memmap_size() isn't accurate and one suggestion to
 improve

On Tue 28-03-17 09:11:37, Wei Yang wrote:
> Hi, masters,
> 
> # What I found
> 
> I found the function calc_memmap_size() may not be that accurate to get the
> pages for memmap.
> 
> The reason is:
> 
> > memmap is allocated on a node base,
> > while the calculation is on a zone base
> 
> This applies both to SPARSEMEM and FLATMEM.
> 
> For example, on my laptop with 6G memory, all the memmap space is allocated
> from ZONE_NORMAL.

Please try to be more specific. Why is this a problem? Are you trying to
fix some bad behavior or you want to make it more optimal?

I am sorry I didn't look closer into your proposal but I am quite busy
and other people are probably in a similar situation. If you want to get
a proper feedback please try to state the problem and be explicit if it
is user observable.
-- 
Michal Hocko
SUSE Labs