linux-kernel - Re: [PATCH] mm, meminit: Serially initialise deferred memory if trace_buf

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Message-ID: <20171115145716.w34jaez5ljb3fssn@dhcp22.suse.cz>
Date:   Wed, 15 Nov 2017 15:57:16 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, yasu.isimatu@...il.com,
        koki.sanagi@...fujitsu.com
Subject: Re: [PATCH] mm, meminit: Serially initialise deferred memory if
 trace_buf_size is specified

On Wed 15-11-17 14:43:14, Mel Gorman wrote:
> On Wed, Nov 15, 2017 at 03:28:16PM +0100, Michal Hocko wrote:
> > On Wed 15-11-17 14:13:29, Mel Gorman wrote:
> > [...]
> > > I doubt anyone well. Even the original reporter appeared to pick that
> > > particular value just to trigger the OOM.
> > 
> > Then why do we care at all? The trace buffer size can be configured from
> > the userspace if it is not sufficiently large IIRC.
> > 
> 
> I guess there is the potential that the trace buffer needs to be large
> enough early on in boot but I'm not sure why it would need to be that large
> to be honest. Bottom line, it's fairly trivial to just serialise meminit
> in the event that it's resized from command line. I'm also ok with just
> leaving this is as a "don't set the buffer that large"

I would be reluctant to touch the code just because of insane kernel
command line option.

That being said, I will not object or block the patch it just seems
unnecessary for most reasonable setups I can think of. If there is a
legitimate usage of such a large trace buffer then I wouldn't oppose.
-- 
Michal Hocko
SUSE Labs