linux-kernel - Re: [PATCH 4/4] mm: numa: Do not mark PTEs pte

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Date:	Thu, 02 Oct 2014 14:58:00 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>
CC:	Dave Jones <davej@...hat.com>, Hugh Dickins <hughd@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Michel Lespinasse <walken@...gle.com>,
	Kirill A Shutemov <kirill.shutemov@...ux.intel.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] mm: numa: Do not mark PTEs pte_numa when splitting
 huge pages

On 10/02/2014 12:36 PM, Linus Torvalds wrote:
> On Thu, Oct 2, 2014 at 6:29 AM, Mel Gorman <mgorman@...e.de> wrote:
>> > This patch reverts 1ba6e0b50b ("mm: numa: split_huge_page: transfer the
>> > NUMA type from the pmd to the pte"). If a huge page is being split due
>> > a protection change and the tail will be in a PROT_NONE vma then NUMA
>> > hinting PTEs are temporarily created in the protected VMA.
> So this is the particular bug I was worried about when tracing through the code.
> 
> Should I just apply this as-is? And mark it for stable, since this has
> been around since 3.8 or so. It would seem to be a very safe change to
> do, regardless of whether this is actually the issue that Dave and
> maybe Sasha are seeing.
> 
> Sasha, I notice that you weren't on the cc for Mel's patches (probably
> because you got added later to the other thread), but they were all
> cc'd to lkml so you should see them there. Or I can forward them
> separately.

I grabbed them and will keep them in my tree for now instead of your
NUMA-chainsaw-massacre patch.

You've also mentioned that while I can tell you if nothing dies, I can't
really tell you if everything is working well. Is there a reasonable way
to easily say if NUMA is working properly? Even something that would just
tell me "your NUMA balancing seems to be sane" would be good.


Thanks,
Sasha
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