linux-kernel - Re: [PATCH 2/2] mm, slab: Extend vm/drop

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Message-ID: <73f18141-7e74-9630-06ff-ac8cf9688e6e@redhat.com>
Date:   Thu, 27 Jun 2019 17:31:58 -0400
From:   Waiman Long <longman@...hat.com>
To:     Roman Gushchin <guro@...com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 2/2] mm, slab: Extend vm/drop_caches to shrink kmem slabs

On 6/27/19 5:24 PM, Roman Gushchin wrote:
>>> 2) what's your long-term vision here? do you think that we need to shrink
>>>    kmem_caches periodically, depending on memory pressure? how a user
>>>    will use this new sysctl?
>> Shrinking the kmem caches under extreme memory pressure can be one way
>> to free up extra pages, but the effect will probably be temporary.
>>> What's the problem you're trying to solve in general?
>> At least for the slub allocator, shrinking the caches allow the number
>> of active objects reported in slabinfo to be more accurate. In addition,
>> this allow to know the real slab memory consumption. I have been working
>> on a BZ about continuous memory leaks with a container based workloads.
>> The ability to shrink caches allow us to get a more accurate memory
>> consumption picture. Another alternative is to turn on slub_debug which
>> will then disables all the per-cpu slabs.
> I see... I agree with Michal here, that extending drop_caches sysctl isn't
> the best idea. Isn't it possible to achieve the same effect using slub sysfs?

Yes, using the slub sysfs interface can be a possible alternative.

Cheers,
Longman