linux-kernel - Re: [PATCH 4/4] mm: numa: Slow PTE scan rate if migration failures occur

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Message-ID: <20150320002311.GG28621@dastard>
Date:	Fri, 20 Mar 2015 11:23:11 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, xfs@....sgi.com,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 4/4] mm: numa: Slow PTE scan rate if migration failures
 occur

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@...morbit.com
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