Re: [PATCH 0/5] mm/memcg: Reduce kmemcache memory accounting overhead

[Roman Gushchin]

On Fri, Apr 09, 2021 at 07:18:37PM -0400, Waiman Long wrote:
> With the recent introduction of the new slab memory controller, we
> eliminate the need for having separate kmemcaches for each memory
> cgroup and reduce overall kernel memory usage. However, we also add
> additional memory accounting overhead to each call of kmem_cache_alloc()
> and kmem_cache_free().
> 
> For workloads that require a lot of kmemcache allocations and
> de-allocations, they may experience performance regression as illustrated
> in [1].
> 
> With a simple kernel module that performs repeated loop of 100,000,000
> kmem_cache_alloc() and kmem_cache_free() of 64-byte object at module
> init. The execution time to load the kernel module with and without
> memory accounting were:
> 
>   with accounting = 6.798s
>   w/o  accounting = 1.758s
> 
> That is an increase of 5.04s (287%). With this patchset applied, the
> execution time became 4.254s. So the memory accounting overhead is now
> 2.496s which is a 50% reduction.

Btw, there were two recent independent report about benchmark results
regression caused by the introduction of the per-object accounting:
1) Xing reported a hackbench regression:
https://lkml.org/lkml/2021/1/13/1277
2) Masayoshi reported a pgbench regression:
https://www.spinics.net/lists/linux-mm/msg252540.html

I wonder if you can run them (or at least one) and attach the result
to the series? It would be very helpful.

Thank you!