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Sun, 28 May 2023 13:20:06 -0700 (PDT) MIME-Version: 1.0 References: <20230527103126.398267-1-linmiaohe@huawei.com> In-Reply-To: From: Yosry Ahmed Date: Sun, 28 May 2023 13:19:30 -0700 Message-ID: Subject: Re: [PATCH] memcg: remove unused mem_cgroup_from_obj() To: Muchun Song Cc: Matthew Wilcox , Miaohe Lin , Vasily Averin , 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 8442FA0013 X-Rspam-User: X-Stat-Signature: ash58ogh1j6pmd1c5u3o889hygh8yrtc X-Rspamd-Server: rspam03 X-HE-Tag: 1685305208-672478 X-HE-Meta: U2FsdGVkX1+Fh9KaSjTNKoZWObUcfB6FpnzA7G9AzvJAuZ45mPjBWCe7NsFq8qU31hiEtKM81SSUsGR7XILYFkEh2tMufuLe07w9y2fUJymt6ZQw3491ewqrFRzbeurPckmfH/FqRJtI+dp23K2NxTwXpEyr7DroeCuwoDiDmxEVTz9nx9LRPaK99T0fNaCGEBdMNH8yKsP9UX/XFWzMxn4rd5yLNyEUJSx6An9vSw9Q3STU/ZRHz+1g0PLguLMl6X1BE3nW7+CF2SH6LV4dsiqe+X4QUvmdVbPPT4Yn/XAcuJZFENXq+ZnUg8RbLPuVnjaGlFrwwUwWvrd5p+2x+jeixQ2wrWNAIublL+dlP16iu1joNXGpCkCZtloWcndwCbdnxUQmz/L6VFNv4k9flw8XRlGTGy9E1QfW2aeL/qU+tnuXJFQ4AL+UkHFEvN7U26aEAVnhGYD8eWMGXzRsOMGtL5LZ334quPKCJjWHSyVYW6F22h76Rjf9rEi3U99a04jw7V33We885S/24MWW12rXxs5Y1IrgOidxLuej8eGtJDKIfvvQgRfjhYmbRuzBy9JtdiHKS0Tyri+Ip/cu7A6cC3RVW0siQA6TWe7wRu4s4hChyIdp/Qp0jD07VeG+W6QM7Qp25A2KOCX6ILn7+VEwj4eS4tvwBcimaE/t6FGAOlFRW+VdFnd5WhO5nLxRSAOk9ZTW6jXA1NMswiLWjptcjgecK2FOekQjFWKLGJbgepmGovAMRf83wvJmnHOCOgLqoYdBDy5AJy2XElO6eAwMuraYHGAzUY9T6o07KS1HEcHwkSGnyxkYlw+eMN2Cr0TSyXn+jbzbdKcidZR7Jxhz1as91/dcAZcg3K5qshKB1O3S74hPfGGHM4Ne7V1i/Ak9gv6rHTbjh3FWqCx0UibWwPlxlRBQsvoZFH9S52vJd0F71Km0mpuYKydGI+50hnvVzoBCwxQ6U2NGDOg I4z8k2oD Ks+l3H+LN52ASiIrlPjRkNNugnOcsewNaaanpkxOXFXZu3b6jEaUaIaqiis94HzDOXRX0UX57JSqVnjZHG5CWFWaxHdrEa7nvg5nbANqeT6dmGDFWZiT73gg3eyxn4W1f43hgx+cj1PZMP3ImH9Q7caZF6Nx76L3HM0+TxMJmPns4cT/vOHhcjjxN6GkeT5Qh+nEyRVC8T+yo9zGrTF9kwmCC5aogm7fjV3qp8X65XBFS1VDPcS4j7Mej8mPxtVuL6yd7FMqfy7ymwoB8ZVomD0qDyRsZ4Fu5Q4Pg3bY3CSTjPaUzDFduxZy/WNEIcuNMvOyJHSMIu52RYZfHbHOrPtsOO8p0dGuYDu0NJ2mldZzgM7qJVsy6hQzo93qs4FA+6urMhqvObfUvu68ZjU4iCusybKCPkNNFlgE+ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, May 28, 2023 at 6:02=E2=80=AFAM Muchun Song = wrote: > > > > > On May 28, 2023, at 02:54, Yosry Ahmed wrote: > > > > On Sat, May 27, 2023 at 8:07=E2=80=AFAM Matthew Wilcox wrote: > >> > >> On Fri, May 26, 2023 at 09:13:05PM -0700, Yosry Ahmed wrote: > >>> On Fri, May 26, 2023 at 9:01=E2=80=AFPM Matthew Wilcox 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 a= nd > >>>>> 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 us= ed > 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 bac= k, > this patch LGTM. Otherwise, let's wait for Vasily. I see, thanks for the context, Muchun! > > Thanks. >