linux-kernel - Re: question on NUMA page migration

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Date:	Sun, 21 Oct 2012 14:30:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Mel Gorman <mel@....ul.ie>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: question on NUMA page migration


* Rik van Riel <riel@...hat.com> wrote:

> On 10/19/2012 09:23 PM, Ingo Molnar wrote:
> >
> >* Rik van Riel <riel@...hat.com> wrote:
> >
> >>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?
> >
> >Which commit(s) worry you specifically?
> 
> One of them would be the commit that introduces MIGRATE_FAULT.

MIGRATE_FAULT is still used.

> Adding it in one patch, and removing it into a next just makes
> things harder on the reviewers.

Yes.

> 03a040f6c17ab81659579ba6abe267c0562097e4

It's still used:

comet:~/tip> git grep MIGRATE_FAULT
include/linux/migrate_mode.h: * MIGRATE_FAULT called from the fault path to migrate-on-fault for mempolicy
include/linux/migrate_mode.h:	MIGRATE_FAULT,
mm/migrate.c:	if (mode != MIGRATE_ASYNC && mode != MIGRATE_FAULT) {
mm/migrate.c:	if (mode == MIGRATE_FAULT) {
mm/migrate.c:		 * MIGRATE_FAULT has an extra reference on the page and
mm/migrate.c:	if ((mode == MIGRATE_ASYNC || mode == MIGRATE_FAULT) && head &&
mm/migrate.c:	if (mode != MIGRATE_ASYNC && mode != MIGRATE_FAULT)
mm/migrate.c:		if (!force || mode == MIGRATE_ASYNC || mode == MIGRATE_FAULT)
mm/migrate.c:	ret = __unmap_and_move(page, newpage, 0, 0, MIGRATE_FAULT);

> If the changesets with NUMA syscalls are still in your tree's 
> history, they should not be submitted as part of the patch 
> series, either.

No, the syscalls have not been there for quite some time.

If you have trouble with any specific commit, please quote the 
specific SHA1 so that I can have a look and resolve any specific 
concerns.

Otherwise, lets continue with the integration?

Thanks,

	Ingo
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