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Date: Fri, 20 Mar 2015 11:23:11 +1100
From: Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH 4/4] mm: numa: Slow PTE scan rate if migration failures
	occur
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, xfs@oss.sgi.com, Linux-MM <linux-mm@kvack.org>, Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>, Andrew Morton <akpm@linux-foundation.org>, ppc-dev <linuxppc-dev@lists.ozlabs.org>, Ingo Molnar <mingo@kernel.org>, Mel Gorman <mgorman@suse.de>

On Thu, Mar 19, 2015 at 04:05:46PM -0700, Linus Torvalds wrote:
> Can you try Mel's change to make it use
> 
>         if (!(vma->vm_flags & VM_WRITE))
> 
> instead of the pte details? Again, on otherwise plain 3.19, just so
> that we have a baseline. I'd be *so* much happer with checking the vma
> details over per-pte details, especially ones that change over the
> lifetime of the pte entry, and the NUMA code explicitly mucks with.

$ sudo perf_3.18 stat -a -r 6 -e migrate:mm_migrate_pages sleep 10

 Performance counter stats for 'system wide' (6 runs):

    266,750      migrate:mm_migrate_pages ( +-  7.43% )

	  10.002032292 seconds time elapsed ( +-  0.00% )

Bit more variance there than the pte checking, but runtime
difference is in the noise - 5m4s vs 4m54s - and profiles are
identical to the pte checking version.

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com

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