From: Vladimir Davydov <vdavydov@parallels.com>
To: Greg Thelen <gthelen@google.com>
Cc: Suleiman Souhlal <suleiman@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>, Hugh Dickins <hughd@google.com>,
Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Motohiro Kosaki <Motohiro.Kosaki@us.fujitsu.com>,
Dave Chinner <david@fromorbit.com>,
Glauber Costa <glommer@gmail.com>, Tejun Heo <tj@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Pavel Emelianov <xemul@parallels.com>,
Konstantin Khorenko <khorenko@parallels.com>,
LKML-MM <linux-mm@kvack.org>,
LKML-cgroups <cgroups@vger.kernel.org>
Subject: Re: [RFC] memory cgroup: weak points of kmem accounting design
Date: Sun, 21 Sep 2014 19:30:10 +0400 [thread overview]
Message-ID: <20140921153010.GB32416@esperanza> (raw)
In-Reply-To: <xr93r3z9ctje.fsf@gthelen.mtv.corp.google.com>
Hi Greg,
On Wed, Sep 17, 2014 at 09:04:00PM -0700, Greg Thelen wrote:
> I've found per memcg per cache type stats useful in answering "why is my
> container oom?" While these are kernel allocations, it is common for
> user space operations to cause these allocations (e.g. lots of open file
> descriptors). So I don't specifically need per memcg slabinfo formatted
> data, but at the least a per memcg per cache type active object count
> would be very useful. Thus I imagine each memcg would have an array of
> slab cache types each with per-cpu active object counters. Per-cpu is
> used to avoid trashing those counters between cpus as objects are
> allocated and freed.
Hmm, that sounds sane. One more argument for the current design.
> As you say only memcg shrinkable cache types would need list heads. I
> assume these per memcg shrinkable object list heads would be per cache
> type per cpu list heads for cache performance. Allocation of a dentry
> today uses the normal slab management structures. In this proposal I
> suspect the dentry would be dual indexed: once in the global slab/slub
> dentry lru and once in the per memcg dentry list. If true, this might
> be a hot path regression allocation speed regression.
>
> Do you have a shrinker design in mind? I suspect this new design would
> involve a per memcg dcache shrinker which grabs a big per-memcg dcache
> lock while walking the dentry list. The classic per superblock
> shrinkers would not used for memcg shrinking.
To be honest, I hadn't elaborated that in my mind when I sent this
e-mail, but now I realize that it doesn't look as if there's an easy way
to implement shrinkers in such a setup efficiently. I thought we could
keep each dentry/inode simultaneously in two list, global and memcg.
However, apart from resulting in memory wastes this, as you pointed out,
would result in a regression in operating on the lrus, which is
unacceptable.
That said, I admit my idea sounds crazy. I think sticking to Glauber's
design and trying to make it work is the best we can do now.
Thanks,
Vladimir
prev parent reply other threads:[~2014-09-21 15:30 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-15 10:44 [RFC] memory cgroup: weak points of kmem accounting design Vladimir Davydov
2014-09-15 19:13 ` Suleiman Souhlal
2014-09-16 8:31 ` Vladimir Davydov
2014-09-18 4:04 ` Greg Thelen
2014-09-21 15:30 ` Vladimir Davydov [this message]
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