linux-kernel - Re: [PATCH] mm: memcontrol: rename memcg_kmem

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Date:   Tue, 14 Feb 2023 10:19:55 -0800
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Muchun Song <muchun.song@...ux.dev>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Dennis Zhou <dennis@...nel.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: memcontrol: rename memcg_kmem_enabled()

On Tue, Feb 14, 2023 at 11:54:35AM +0800, Muchun Song wrote:
> 
> 
> > On Feb 14, 2023, at 03:29, Roman Gushchin <roman.gushchin@...ux.dev> wrote:
> > 
> > Currently there are two kmem-related helper functions with a confusing
> > semantics: memcg_kmem_enabled() and mem_cgroup_kmem_disabled().
> > 
> > The problem is that an obvious expectation
> > memcg_kmem_enabled() == !mem_cgroup_kmem_disabled(),
> > can be false.
> > 
> > mem_cgroup_kmem_disabled() is similar to mem_cgroup_disabled(): it
> > returns true only if CONFIG_MEMCG_KMEM is not set or the kmem
> > accounting is disabled using a boot time kernel option
> > "cgroup.memory=nokmem". It never changes the value dynamically.
> > 
> > memcg_kmem_enabled() is different: it always returns false until
> > the first non-root memory cgroup will get online (assuming the kernel
> > memory accounting is enabled). It's goal is to improve the performance
> > on systems without the cgroupfs mounted/memory controller enabled or
> > on the systems with only the root memory cgroup.
> > 
> > To make things more obvious and avoid potential bugs, let's rename
> > memcg_kmem_enabled() to memcg_kmem_online().
> > 
> > Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> 
> It's more clear.
> 
> Acked-by: Muchun Song <songmuchun@...edance.com>

Thank you!

> 
> BTW, I also dislike the name of mem_cgroup_kmem_disabled, it is not
> harmonious with memcg_kmem_enabled since the prefix of one is "mem_cgroup",
> another is "memcg". Maybe we could make them more consistent. Anyway, it
> is not related to this patch.

It's a pair to mem_cgroup_disabled().

Thanks!