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

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Message-ID: <f22001bb-e474-4ddb-8440-2668e6cec000@linux.alibaba.com>
Date:   Tue, 14 Nov 2023 19:11:56 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     "Huang, Ying" <ying.huang@...el.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



On 11/14/2023 9:12 AM, Huang, Ying wrote:
> 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.

Not sure I get you here. In should_numa_migrate_memory(), it will use 
last CPU id, last PID and group numa faults to determine if this page 
can be migrated to the target node. So for large folio, a precise folio 
sharers check can make the numa faults of a group more accurate, which 
is enough for should_numa_migrate_memory() to make a decision?

Could you provide a more detailed description of the algorithm you would 
like to change for large folio? Thanks.

> And, as a performance improvement patch, some performance data needs to

Do you have some benchmark recommendation? I know the the autonuma can 
not support large folio now.

> be provided.  And, the effect of shared folio detection needs to be
> tested too