linux-kernel - Re: [PATCH 00/16] The new slab memory controller

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Message-ID: <20191022133148.GP9379@dhcp22.suse.cz>
Date:   Tue, 22 Oct 2019 15:31:48 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        Shakeel Butt <shakeelb@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Waiman Long <longman@...hat.com>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 00/16] The new slab memory controller

On Thu 17-10-19 17:28:04, Roman Gushchin wrote:
> This patchset provides a new implementation of the slab memory controller,
> which aims to reach a much better slab utilization by sharing slab pages
> between multiple memory cgroups. Below is the short description of the new
> design (more details in commit messages).
> 
> Accounting is performed per-object instead of per-page. Slab-related
> vmstat counters are converted to bytes. Charging is performed on page-basis,
> with rounding up and remembering leftovers.
> 
> Memcg ownership data is stored in a per-slab-page vector: for each slab page
> a vector of corresponding size is allocated. To keep slab memory reparenting
> working, instead of saving a pointer to the memory cgroup directly an
> intermediate object is used. It's simply a pointer to a memcg (which can be
> easily changed to the parent) with a built-in reference counter. This scheme
> allows to reparent all allocated objects without walking them over and changing
> memcg pointer to the parent.
> 
> Instead of creating an individual set of kmem_caches for each memory cgroup,
> two global sets are used: the root set for non-accounted and root-cgroup
> allocations and the second set for all other allocations. This allows to
> simplify the lifetime management of individual kmem_caches: they are destroyed
> with root counterparts. It allows to remove a good amount of code and make
> things generally simpler.

What is the performance impact? Also what is the effect on the memory
reclaim side and the isolation. I would expect that mixing objects from
different cgroups would have a negative/unpredictable impact on the
memcg slab shrinking.
-- 
Michal Hocko
SUSE Labs