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

[Waiman Long]

On 4/12/21 3:05 PM, Roman Gushchin wrote:
> 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.

Actually, it was a bug reported filed by Masayoshi-san that triggered me 
to work on reducing the memory accounting overhead. He is also in the cc 
line and so is aware of that. I will cc Xing in my v2 patch.

Cheers,
Longman