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

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Date:   Mon, 20 Nov 2017 17:04:29 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        YASUAKI ISHIMATSU <yasu.isimatu@...il.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-kernel@...r.kernel.org, koki.sanagi@...fujitsu.com,
        Steve Sistare <steven.sistare@...cle.com>
Subject: Re: [PATCH] mm, meminit: Serially initialise deferred memory if
 trace_buf_size is specified

On Fri, 17 Nov 2017 13:19:56 -0500 Pavel Tatashin <pasha.tatashin@...cle.com> wrote:

> On Thu, Nov 16, 2017 at 5:06 AM, Mel Gorman <mgorman@...hsingularity.net> wrote:
> > 4. Put a check into the page allocator slowpath that triggers serialised
> >    init if the system is booting and an allocation is about to fail. It
> >    would be such a cold path that it would never be noticable although it
> >    would leave dead code in the kernel image once boot had completed
> 
> Hi Mel,
> 
> The forth approach is the best as it is seamless for admins and
> engineers, it will also work on any system configuration with any
> parameters without any special involvement.

Apart from what-mel-said, I'd be concerned that this failsafe would
almost never get tested.  We should find some way to ensure that this
code gets exercised in some people's kernels on a permanent basis and
I'm not sure how to do that.

One option might be to ask Fengguang to add the occasional
test_pavels_stuff=1 to the kernel boot commandline.  That's better
than nothing but 0-day only runs on a small number of machine types.