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

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Date:   Mon, 13 Nov 2023 20:10:34 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     David Hildenbrand <david@...hat.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        <akpm@...ux-foundation.org>
CC:     <ying.huang@...el.com>, <willy@...radead.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [RFC PATCH] mm: support large folio numa balancing



On 2023/11/13 18:53, David Hildenbrand wrote:
> 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.
> 
> As spelled out in the commit you are referencing:
> 
> commit 6695cf68b15c215d33b8add64c33e01e3cbe236c
> Author: Kefeng Wang <wangkefeng.wang@...wei.com>
> Date:   Thu Sep 21 15:44:14 2023 +0800
> 
>      mm: memory: use a folio in do_numa_page()
>      Numa balancing only try to migrate non-compound page in 
> do_numa_page(),
>      use a folio in it to save several compound_head calls, note we use
>      folio_estimated_sharers(), it is enough to check the folio sharers 
> since
>      only normal page is handled, if large folio numa balancing is 
> supported, a
>      precise folio sharers check would be used, no functional change 
> intended.
> 
> 
> I'll send WIP patches for one approach that can improve the situation 
> soonish.

When convert numa balance to use folio, I make similar change, it works
with large anon folio(test with v5), but David's precise folio sharers
should be merged firstly, also if a large folio shared by many process,
we maybe split it, don't sure about it, this need some evaluation.