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

From: Dave Chinner <[email-masked]>
Date: Fri, 20 Mar 2015 11:23:11 +1100

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
[email-masked]