From: Yosry Ahmed <yosryahmed@google.com>
To: Muchun Song <muchun.song@linux.dev>
Cc: Matthew Wilcox <willy@infradead.org>,
Miaohe Lin <linmiaohe@huawei.com>,
Vasily Averin <vasily.averin@linux.dev>,
hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev,
shakeelb@google.com, akpm@linux-foundation.org,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: remove unused mem_cgroup_from_obj()
Date: Sun, 28 May 2023 13:19:30 -0700 [thread overview]
Message-ID: <CAJD7tkb+Y6PXHEVkmXyfMSXh=kY_T-qxvJFv=nF-m0ZYZv5Ryw@mail.gmail.com> (raw)
In-Reply-To: <D2B59104-B602-45A3-B938-AE5DC67BAC98@linux.dev>
On Sun, May 28, 2023 at 6:02 AM Muchun Song <muchun.song@linux.dev> wrote:
>
>
>
> > On May 28, 2023, at 02:54, Yosry Ahmed <yosryahmed@google.com> wrote:
> >
> > On Sat, May 27, 2023 at 8:07 AM Matthew Wilcox <willy@infradead.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@infradead.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.
>
> I think it is because *init_net* which is not allocated from slab meant
> its address does not belong to linear mapping addresses on arm64. However,
> virt_to_page() is only applicable to linear mapping addresses. So,
> mem_cgroup_from_slab_obj() is not sufficient. mem_cgroup_from_obj() is used
> in this case, which will use vmalloc_to_page() for the page associated
> with *init_net*. If Vasily does not want to bring commit 1d0403d20f6c back,
> this patch LGTM. Otherwise, let's wait for Vasily.
I see, thanks for the context, Muchun!
>
> Thanks.
>
prev parent reply other threads:[~2023-05-28 20:20 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-27 10:31 Miaohe Lin
2023-05-27 3:55 ` Yosry Ahmed
2023-05-27 4:00 ` Matthew Wilcox
2023-05-27 4:13 ` Yosry Ahmed
2023-05-27 15:07 ` Matthew Wilcox
2023-05-27 18:54 ` Yosry Ahmed
2023-05-28 13:01 ` Muchun Song
2023-05-28 19:36 ` Matthew Wilcox
2023-05-29 18:53 ` Shakeel Butt
2023-05-28 20:19 ` Yosry Ahmed [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAJD7tkb+Y6PXHEVkmXyfMSXh=kY_T-qxvJFv=nF-m0ZYZv5Ryw@mail.gmail.com' \
--to=yosryahmed@google.com \
--cc=akpm@linux-foundation.org \
--cc=cgroups@vger.kernel.org \
--cc=hannes@cmpxchg.org \
--cc=linmiaohe@huawei.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
--cc=muchun.song@linux.dev \
--cc=roman.gushchin@linux.dev \
--cc=shakeelb@google.com \
--cc=vasily.averin@linux.dev \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox