linux-kernel - Re: [PATCH v3 2/3] mm/numa: no task_numa

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Message-ID: <13318f5e-6a76-49ca-8c7a-9f461061d1d7@redhat.com>
Date: Fri, 9 Aug 2024 17:29:43 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "Huang, Ying" <ying.huang@...el.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, Yang Shi <shy828301@...il.com>,
 Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v3 2/3] mm/numa: no task_numa_fault() call if PMD is
 changed

On 09.08.24 16:59, Zi Yan wrote:
> When handling a numa page fault, task_numa_fault() should be called by a
> process that restores the page table of the faulted folio to avoid
> duplicated stats counting. Commit c5b5a3dd2c1f ("mm: thp: refactor NUMA
> fault handling") restructured do_huge_pmd_numa_page() and did not avoid
> task_numa_fault() call in the second page table check after a numa
> migration failure. Fix it by making all !pmd_same() return immediately.
> 
> This issue can cause task_numa_fault() being called more than necessary
> and lead to unexpected numa balancing results (It is hard to tell whether
> the issue will cause positive or negative performance impact due to
> duplicated numa fault counting).
> 
> Reported-by: "Huang, Ying" <ying.huang@...el.com>
> Closes: https://lore.kernel.org/linux-mm/87zfqfw0yw.fsf@yhuang6-desk2.ccr.corp.intel.com/
> Fixes: c5b5a3dd2c1f ("mm: thp: refactor NUMA fault handling")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb