linux-kernel - Re: [RFC PATCH] mm: support large folio numa balancing

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Date:   Tue, 14 Nov 2023 09:12:05 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Hildenbrand <david@...hat.com>
Cc:     akpm@...ux-foundation.org, wangkefeng.wang@...wei.com,
        willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH] mm: support large folio numa balancing

David Hildenbrand <david@...hat.com> writes:

> On 13.11.23 11:45, Baolin Wang wrote:
>> Currently, the file pages already support large folio, and supporting for
>> anonymous pages is also under discussion[1]. Moreover, the numa balancing
>> code are converted to use a folio by previous thread[2], and the migrate_pages
>> function also already supports the large folio migration.
>> So now I did not see any reason to continue restricting NUMA
>> balancing for
>> large folio.
>
> I recall John wanted to look into that. CCing him.
>
> I'll note that the "head page mapcount" heuristic to detect sharers will
> now strike on the PTE path and make us believe that a large folios is
> exclusive, although it isn't.

Even 4k folio may be shared by multiple processes/threads.  So, numa
balancing uses a multi-stage node selection algorithm (mostly
implemented in should_numa_migrate_memory()) to identify shared folios.
I think that the algorithm needs to be adjusted for PTE mapped large
folio for shared folios.

And, as a performance improvement patch, some performance data needs to
be provided.  And, the effect of shared folio detection needs to be
tested too.

--
Best Regards,
Huang, Ying