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SubjectRe: [PATCH] sched,numa,mm: revert to checking pmd/pte_write instead of VMA flags
On Thu, Sep 08, 2016 at 09:30:53PM -0400, Rik van Riel wrote:
> Commit 4d9424669946 ("mm: convert p[te|md]_mknonnuma and remaining
> page table manipulations") changed NUMA balancing from _PAGE_NUMA
> to using PROT_NONE, and was quickly found to introduce a regression
> with NUMA grouping.
> It was followed up by these changesets:
> 53da3bc2ba9e ("mm: fix up numa read-only thread grouping logic")
> bea66fbd11af ("mm: numa: group related processes based on VMA flags instead of page table flags")
> b191f9b106ea ("mm: numa: preserve PTE write permissions across a NUMA hinting fault")
> The first of those two changesets try alternate approaches to NUMA
> grouping, which apparently do not work as well as looking at the PTE
> write permissions.
> The latter patch preserves the PTE write permissions across a NUMA
> protection fault. However, it forgets to revert the condition for
> whether or not to group tasks together back to what it was before
> 3.19, even though the information is now preserved in the page tables
> once again.
> This patch brings the NUMA grouping heuristic back to what it was
> before changeset 4d9424669946, which the changelogs of subsequent
> changesets suggest worked best.
> We have all the information again. We should probably use it.

Patch looks ok other than the comment above the second hunk being out of
date. Out of curiousity, what workload benefitted from this? I saw a mix
of marginal results when I ran this on a 2-socket and 4-socket box.

Mel Gorman

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