From: Roman Gushchin <guro@fb.com>
To: Yang Shi <shy828301@gmail.com>
Cc: Christopher Lameter <cl@linux.com>,
Waiman Long <longman@redhat.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Jonathan Corbet <corbet@lwn.net>,
Luis Chamberlain <mcgrof@kernel.org>,
"Kees Cook" <keescook@chromium.org>,
Johannes Weiner <hannes@cmpxchg.org>,
"Michal Hocko" <mhocko@kernel.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Shakeel Butt <shakeelb@google.com>,
"Andrea Arcangeli" <aarcange@redhat.com>
Subject: Re: [PATCH 2/2] mm, slab: Extend vm/drop_caches to shrink kmem slabs
Date: Fri, 28 Jun 2019 17:30:46 +0000 [thread overview]
Message-ID: <20190628173040.GA11971@tower.DHCP.thefacebook.com> (raw)
In-Reply-To: <CAHbLzkr+EJWgAQ9VhAdeTtMx+11=AX=mVVEvC-0UihROf2J+PA@mail.gmail.com>
On Fri, Jun 28, 2019 at 10:16:13AM -0700, Yang Shi wrote:
> On Fri, Jun 28, 2019 at 8:32 AM Christopher Lameter <cl@linux.com> wrote:
> >
> > On Thu, 27 Jun 2019, Roman Gushchin wrote:
> >
> > > so that objects belonging to different memory cgroups can share the same page
> > > and kmem_caches.
> > >
> > > It's a fairly big change though.
> >
> > Could this be done at another level? Put a cgoup pointer into the
> > corresponding structures and then go back to just a single kmen_cache for
> > the system as a whole? You can still account them per cgroup and there
> > will be no cleanup problem anymore. You could scan through a slab cache
> > to remove the objects of a certain cgroup and then the fragmentation
> > problem that cgroups create here will be handled by the slab allocators in
> > the traditional way. The duplication of the kmem_cache was not designed
> > into the allocators but bolted on later.
>
> I'm afraid this may bring in another problem for memcg page reclaim.
> When shrinking the slabs, the shrinker may end up scanning a very long
> list to find out the slabs for a specific memcg. Particularly for the
> count operation, it may have to scan the list from the beginning all
> the way down to the end. It may take unbounded time.
>
> When I worked on THP deferred split shrinker problem, I used to do
> like this, but it turns out it may take milliseconds to count the
> objects on the list, but it may just need reclaim a few of them.
I don't think the shrinker mechanism should be altered. Shrinker lists
already contain individual objects, and I don't see any reasons, why
these objects can't reside on a shared set of pages.
What we're discussing is that it's way too costly (under some conditions)
to have many sets of kmem_caches, if each of them is containing only
few objects.
Thanks!
next prev parent reply other threads:[~2019-06-28 17:31 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-24 17:42 [PATCH 0/2] mm, slab: Extend vm/drop_caches to shrink kmem slabs Waiman Long
2019-06-24 17:42 ` [PATCH 1/2] mm, memcontrol: Add memcg_iterate_all() Waiman Long
2019-06-27 15:07 ` Michal Hocko
2019-06-27 21:03 ` Waiman Long
2019-06-28 7:10 ` Michal Hocko
2019-06-24 17:42 ` [PATCH 2/2] mm, slab: Extend vm/drop_caches to shrink kmem slabs Waiman Long
2019-06-26 20:19 ` Roman Gushchin
2019-06-27 20:57 ` Waiman Long
2019-06-27 21:24 ` Roman Gushchin
2019-06-27 21:31 ` Waiman Long
2019-06-28 15:32 ` Christopher Lameter
2019-06-28 16:33 ` Roman Gushchin
2019-06-28 17:16 ` Yang Shi
2019-06-28 17:30 ` Roman Gushchin [this message]
2019-06-27 21:25 ` Luis Chamberlain
2019-06-27 15:15 ` Michal Hocko
2019-06-27 21:16 ` Waiman Long
2019-06-28 7:31 ` Michal Hocko
2019-07-02 18:41 ` Waiman Long
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