linux-kernel - Re: [PATCH 3/5] mm, page_owner: copy page owner info during migration

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Date:	Thu, 19 Nov 2015 17:44:12 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Minchan Kim <minchan@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 3/5] mm, page_owner: copy page owner info during migration

On 11/08/2015 10:29 PM, Hugh Dickins wrote:
>
> Would it be possible to move that line into migrate_page_copy()?
>
> I don't think it's wrong where you placed it, but that block is really
> about resetting the old page ready for freeing, and I'd prefer to keep
> all the transference of properties from old to new in migrate_page_copy()
> if we can.

OK, makes sense, will do in v2.

> But check how that behaves in the migrate_misplaced_transhuge_page()
> case: I haven't studied long enough, but I think you may have been missing
> to copy_page_owner in that case;

You're right, I missed that path :/

> but beware of its "fail_putback", which
> for some things nastily entails undoing what's already been done.

Yeah, I think I don't need to reset page owner info in the fail_putback 
path, for the same reason I don't reset it from the old page when 
migration is successful. The page is going to be freed anyway, and if it 
somehow hits a bug before that, we will still have something to print 
(after patch 5).

Thanks!

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