Re: [PATCH v2 4/5] mm: FLEXIBLE_THP for improved performance

[Huang, Ying]

Ryan Roberts <ryan.roberts@xxxxxxx> writes:

> Introduce FLEXIBLE_THP feature, which allows anonymous memory to be
> allocated in large folios of a specified order. All pages of the large
> folio are pte-mapped during the same page fault, significantly reducing
> the number of page faults. The number of per-page operations (e.g. ref
> counting, rmap management lru list management) are also significantly
> reduced since those ops now become per-folio.

I likes the idea to share as much code as possible between large
(anonymous) folio and THP.  Finally, THP becomes just a special kind of
large folio.

Although we can use smaller page order for FLEXIBLE_THP, it's hard to
avoid internal fragmentation completely.  So, I think that finally we
will need to provide a mechanism for the users to opt out, e.g.,
something like "always madvise never" via
/sys/kernel/mm/transparent_hugepage/enabled.  I'm not sure whether it's
a good idea to reuse the existing interface of THP.

Best Regards,
Huang, Ying