Re: [RFC 0/2] An attempt to improve SLUB on NUMA / under memory pressure

[Jay Patel]

On Mon, 2023-07-24 at 04:09 +0900, Hyeonggon Yoo wrote:
> Hello folks,
> 
> This series is motivated by kernel test bot report [1] on Jay's patch
> that modifies slab order. While the patch was not merged and not in
> the
> final form, I think it was a good lesson that changing slab order has
> more
> impacts on performance than we expected.
> 
> While inspecting the report, I found some potential points to improve
> SLUB. [2] It's _potential_ because it shows no improvements on
> hackbench.
> but I believe more realistic workloads would benefit from this. Due
> to
> lack of resources and lack of my understanding of *realistic*
> workloads,
> I am asking you to help evaluating this together.

Hi Hyeonggon,
I tried hackbench test on Powerpc machine with 16 cpus but
got ~32% of Regression with patch.

Results as 

+-------+----+---------+------------+------------+
|       |    | Normal  | With Patch |            |
+-------+----+---------+------------+------------+
| Amean | 1  | 1.3700  | 2.0353     | ( -32.69%) |
| Amean | 4  | 5.1663  | 7.6563     | (- 32.52%) |
| Amean | 7  | 8.9180  | 13.3353    | ( -33.13%) |
| Amean | 12 | 15.4290 | 23.0757    | ( -33.14%) |
| Amean | 21 | 27.3333 | 40.7823    | ( -32.98%) |
| Amean | 30 | 38.7677 | 58.5300    | ( -33.76%) |
| Amean | 48 | 62.2987 | 92.9850    | ( -33.00%) |
| Amean | 64 | 82.8993 | 123.4717   | ( -32.86%) |
+-------+----+---------+------------+------------+

Thanks
Jay Patel
> 
> It only consists of two patches. Patch #1 addresses inaccuracy in
> SLUB's heuristic, which can negatively affect workloads' performance
> when large folios are not available from buddy.
> 
> Patch #2 changes SLUB's behavior when there are no slabs available on
> the
> local node's partial slab list, increasing NUMA locality when there
> are
> available memory (without reclamation) on the local node from buddy.
> 
> This is early state, but I think it's a good enough to start
> discussion.
> Any feedbacks and ideas are welcome. Thank you in advance!
> 
> Hyeonggon
> 
> https://lore.kernel.org/linux-mm/202307172140.3b34825a-oliver.sang@xxxxxxxxx
> [1]
> https://lore.kernel.org/linux-mm/CAB=+i9S6Ykp90+4N1kCE=hiTJTE4wzJDi8k5pBjjO_3sf0aeqg@xxxxxxxxxxxxxx
> [2]
> 
> Hyeonggon Yoo (2):
>   Revert "mm, slub: change percpu partial accounting from objects to
>     pages"
>   mm/slub: prefer NUMA locality over slight memory saving on NUMA
>     machines
> 
>  include/linux/slub_def.h |  2 --
>  mm/slab.h                |  6 ++++
>  mm/slub.c                | 76 ++++++++++++++++++++++++++----------
> ----
>  3 files changed, 55 insertions(+), 29 deletions(-)
>