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

To: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 4/4] mm: numa: Slow PTE scan rate if migration failures occur
From: Mel Gorman <mgorman@xxxxxxx>
Date: Fri, 20 Mar 2015 10:12:46 +0000
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Aneesh Kumar <aneesh.kumar@xxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Linux-MM <linux-mm@xxxxxxxxx>, xfs@xxxxxxxxxxx, ppc-dev <linuxppc-dev@xxxxxxxxxxxxxxxx>
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References: <20150317205104.GA28621@dastard> <CA+55aFzSPcNgxw4GC7aAV1r0P5LniyVVC66COz=3cgMcx73Nag@xxxxxxxxxxxxxx> <20150317220840.GC28621@dastard> <CA+55aFwne-fe_Gg-_GTUo+iOAbbNpLBa264JqSFkH79EULyAqw@xxxxxxxxxxxxxx> <CA+55aFy-Mw74rAdLMMMUgnsG3ZttMWVNGz7CXZJY7q9fqyRYfg@xxxxxxxxxxxxxx> <CA+55aFyxA9u2cVzV+S7TSY9ZvRXCX=z22YAbi9mdPVBKmqgR5g@xxxxxxxxxxxxxx> <20150319224143.GI10105@dastard> <CA+55aFy5UeNnFUTi619cs3b9Up2NQ1wbuyvcCS614+o3=z=wBQ@xxxxxxxxxxxxxx> <20150320002311.GG28621@dastard> <CA+55aFyqXDVv9JkkhvM26x6PC5V82corR7HQNxmkeGZjOCxD=A@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Mar 19, 2015 at 06:29:47PM -0700, Linus Torvalds wrote:
> And the VM_WRITE test should be stable and not have any subtle
> interaction with the other changes that the numa pte things
> introduced. It would be good to see if the profiles then pop something
> *else* up as the performance difference (which I'm sure will remain,
> since the 7m50s was so far off).
> 

As a side-note, I did test a patch that checked pte_write and preserved
it across both faults and setting the protections. It did not alter
migration activity much but there was a  drop in minor faults - 20% drop in
autonumabench, 58% drop in xfsrepair workload. I'm assuming this is due to
refaults to mark pages writable.  The patch looks and is hacky so I won't
post it to save people bleaching their eyes. I'll spend some time soon
(hopefully today) at a smooth way of falling through to WP checks after
trapping a NUMA fault.

-- 
Mel Gorman
SUSE Labs

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