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

[Huang, Ying]

David Hildenbrand <david@xxxxxxxxxx> 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