linux-kernel - Re: [PATCH] memcg: remove unused mem_cgroup_from

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJD7tkZ2Q1ZCqNchpiiC6FCE08dYH6tzANA=VqujeDgT8YhRUA@mail.gmail.com>
Date:   Sat, 27 May 2023 11:54:50 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Miaohe Lin <linmiaohe@...wei.com>,
        Vasily Averin <vasily.averin@...ux.dev>, hannes@...xchg.org,
        mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
        akpm@...ux-foundation.org, muchun.song@...ux.dev,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: remove unused mem_cgroup_from_obj()

On Sat, May 27, 2023 at 8:07 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Fri, May 26, 2023 at 09:13:05PM -0700, Yosry Ahmed wrote:
> > On Fri, May 26, 2023 at 9:01 PM Matthew Wilcox <willy@...radead.org> wrote:
> > >
> > > On Sat, May 27, 2023 at 06:31:26PM +0800, Miaohe Lin wrote:
> > > > The function mem_cgroup_from_obj() is not used anymore. Remove it and
> > > > clean up relevant comments.
> > >
> > > You should have looked at the git history to see why it was created
> > > and who used it.
> > >
> > > Shakeel, Vasily, are you going to retry adding commit 1d0403d20f6c?
> >
> > That commit did not introduce the function though, no? It was
> > introduced before it and replaced by other variants over time (like
> > mem_cgroup_from_slab_obj()). It looks like that commit was reverted ~9
> > months ago. We can always bring it back if/when needed.
>
> The commit immediately preceding it is fc4db90fe71e.
>
> Of course we can bring it back.  It's just code.  But avoiding
> unnecessary churn is also good.  Let's wait to hear from Vasily.
>
> > It also looks to me that 1d0403d20f6c was using mem_cgroup_from_obj()
> > on a struct net object, which is allocated in net_alloc() from a slab
> > cache, so mem_cgroup_from_slab_obj() should be sufficient, no?
>
> Clearly not.

I dived deeper into the history on LKML, and you are right:
https://lore.kernel.org/all/Yp4F6n2Ie32re7Ed@qian/

I still do not understand why mem_cgroup_from_slab_obj() would not be
sufficient, so I am hoping Vasily or Shakeel can help me understand
here. Seems to be something arch-specific.

Thanks for digging this up, Matthew.