linux-kernel - Re: question on NUMA page migration

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Message-ID: <50819CED.30803@redhat.com>
Date:	Fri, 19 Oct 2012 14:33:17 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Mel Gorman <mel@....ul.ie>,
	Linux kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: question on NUMA page migration

On 10/19/2012 01:53 PM, Peter Zijlstra wrote:
> On Fri, 2012-10-19 at 13:13 -0400, Rik van Riel wrote:

>> Another alternative might be to do the put_page inside
>> do_prot_none_numa().  That would be analogous to do_wp_page
>> disposing of the old page for the caller.
>
> It'd have to be inside migrate_misplaced_page(), can't do before
> isolate_lru_page() or the page might disappear. Doing it after is
> (obviously) too late.

Keeping an extra refcount on the page might _still_
result in it disappearing from the process by some
other means, in-between you grabbing the refcount
and invoking migration of the page.

>> I am not real happy about NUMA migration introducing its own
>> migration mode...
>
> You didn't seem to mind too much earlier, but I can remove it if you
> want.

Could have been reviewing fatigue :)

And yes, it would have been nice to not have a special
migration mode for sched/numa.

Speaking of, when do you guys plan to submit a (cleaned up)
version of the sched/numa patch series for review on lkml?

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