From: Waiman Long <longman@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Christoph Lameter <cl@linux.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>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
linux-mm@kvack.org, linux-doc@vger.kernel.org,
linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, Roman Gushchin <guro@fb.com>,
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: Tue, 2 Jul 2019 14:41:43 -0400 [thread overview]
Message-ID: <eeca4ef9-1b62-dada-3d31-c247cb0b137f@redhat.com> (raw)
In-Reply-To: <20190628073128.GC2751@dhcp22.suse.cz>
On 6/28/19 3:31 AM, Michal Hocko wrote:
> On Thu 27-06-19 17:16:04, Waiman Long wrote:
>> On 6/27/19 11:15 AM, Michal Hocko wrote:
>>> On Mon 24-06-19 13:42:19, Waiman Long wrote:
>>>> With the slub memory allocator, the numbers of active slab objects
>>>> reported in /proc/slabinfo are not real because they include objects
>>>> that are held by the per-cpu slab structures whether they are actually
>>>> used or not. The problem gets worse the more CPUs a system have. For
>>>> instance, looking at the reported number of active task_struct objects,
>>>> one will wonder where all the missing tasks gone.
>>>>
>>>> I know it is hard and costly to get a real count of active objects.
>>> What exactly is expensive? Why cannot slabinfo reduce the number of
>>> active objects by per-cpu cached objects?
>>>
>> The number of cachelines that needs to be accessed in order to get an
>> accurate count will be much higher if we need to iterate through all the
>> per-cpu structures. In addition, accessing the per-cpu partial list will
>> be racy.
> Why is all that a problem for a root only interface that should be used
> quite rarely (it is not something that you should be reading hundreds
> time per second, right)?
That can be true. Anyway, I have posted a new patch to use the existing
<slab>/shrink sysfs file to perform memcg cache shrinking as well. So I
am not going to pursue this patch.
Thanks,
Longman
prev parent reply other threads:[~2019-07-02 18:41 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
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 [this message]
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