linux-kernel - Re: [PATCH 3/6] mm/page_owner: copy last_migrate_reason in copy_page

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Message-ID: <20160512025858.GC8215@js1304-P5Q-DELUXE>
Date:	Thu, 12 May 2016 11:58:58 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	mgorman@...hsingularity.net, Minchan Kim <minchan@...nel.org>,
	Alexander Potapenko <glider@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] mm/page_owner: copy last_migrate_reason in
 copy_page_owner()

On Tue, May 10, 2016 at 05:13:12PM +0200, Vlastimil Babka wrote:
> On 05/03/2016 07:23 AM, js1304@...il.com wrote:
> >From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> >Currently, copy_page_owner() doesn't copy all the owner information.
> >It skips last_migrate_reason because copy_page_owner() is used for
> >migration and it will be properly set soon. But, following patch
> >will use copy_page_owner() and this skip will cause the problem that
> >allocated page has uninitialied last_migrate_reason. To prevent it,
> >this patch also copy last_migrate_reason in copy_page_owner().
> 
> Hmm it's a corner case, but if the "new" page was dumped e.g. due to
> a bug during the migration, is the copied migrate reason from the
> "old" page actually meaningful? I'd say it might be misleading and
> it's simpler to just make sure it's initialized to -1.

Hmm... if it is the case, other fields are also misleading. I think
that we can tolerate this corner case and keeping function semantic as
function name suggests is better practice.

Thanks.