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

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Date:   Mon, 12 Apr 2021 10:47:22 -0700
From:   Roman Gushchin <guro@...com>
To:     Waiman Long <llong@...hat.com>
CC:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        <linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
        <linux-mm@...ck.org>, Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Chris Down <chris@...isdown.name>,
        Yafang Shao <laoar.shao@...il.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Masayoshi Mizuma <msys.mizuma@...il.com>
Subject: Re: [PATCH 0/5] mm/memcg: Reduce kmemcache memory accounting overhead

On Mon, Apr 12, 2021 at 10:03:13AM -0400, Waiman Long wrote:
> On 4/9/21 9:51 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.
> > Hi Waiman!
> > 
> > Thank you for working on it, it's indeed very useful!
> > A couple of questions:
> > 1) did your config included lockdep or not?
> The test kernel is based on a production kernel config and so lockdep isn't
> enabled.
> > 2) do you have a (rough) estimation how much each change contributes
> >     to the overall reduction?
> 
> I should have a better breakdown of the effect of individual patches. I
> rerun the benchmarking module with turbo-boosting disabled to reduce
> run-to-run variation. The execution times were:
> 
> Before patch: time = 10.800s (with memory accounting), 2.848s (w/o
> accounting), overhead = 7.952s
> After patch 2: time = 9.140s, overhead = 6.292s
> After patch 3: time = 7.641s, overhead = 4.793s
> After patch 5: time = 6.801s, overhead = 3.953s

Thank you! If there will be v2, I'd include this information into commit logs.

> 
> Patches 1 & 4 are preparatory patches that should affect performance.
> 
> So the memory accounting overhead was reduced by about half.

This is really great!

Thanks!