linux-kernel - Re: [rfc] forked kernel task and mm structures imbalanced on NUMA

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Date:	Tue, 1 Jun 2010 18:20:25 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Lee@...stfloor.org,
	Schermerh@...stfloor.org
Subject: Re: [rfc] forked kernel task and mm structures imbalanced on NUMA

On Wed, Jun 02, 2010 at 01:59:43AM +1000, Nick Piggin wrote:
> On Tue, Jun 01, 2010 at 05:48:10PM +0200, Andi Kleen wrote:
> > Nick Piggin <npiggin@...e.de> writes:
> > 
> > > This isn't really a new problem, and I don't know how important it is,
> > > but I recently came across it again when doing some aim7 testing with
> > > huge numbers of tasks.
> > 
> > Seems reasonable. Of course you need to at least 
> > save/restore the old CPU policy, and use a subset of it.
> 
> The mpolicy? My patch does that (mpol_prefer_cpu_start/end). The real
> problem is that it can actually violate the parent's mempolicy. For
> example MPOL_BIND and cpus_allowed set on a node outside the mempolicy.

I don't see where you store 'old', but maybe I missed it.

> > slightly more difficult. The advantage would be that on multiple
> > migrations it would follow. And it would be a bit slower for
> > the initial case.
> 
> Migrate what on touch? Talking mainly about kernel memory structures,
> task_struct, mm, vmas, page tables, kernel stack, etc.

Migrate task_struct, mm, vmas, page tables, kernel stack
on reasonable touch. As long as they are not shared it shouldn't
be too difficult.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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