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From: Muchun Song In-Reply-To: Date: Sun, 28 May 2023 21:01:37 +0800 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-Transfer-Encoding: quoted-printable Message-Id: References: <20230527103126.398267-1-linmiaohe@huawei.com> To: Yosry Ahmed X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3605F140002 X-Stat-Signature: rbj4hbxf5fn6egbae3zcqt6i6koj73hn X-HE-Tag: 1685278937-917488 X-HE-Meta: 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 Vk1KszLL KNl2dumjMDhSwaDPHZTkfewZQgiDwCUTTzqVZxt9K1MHPIEEFymSr6GfDka/eGI3R3etOVaSqeIDm9FjBexxuPzshwo2MJBJs2QQduiFX2HgZDWRFOiV8qdvfvso/Nm4CNHcIH461tBQwtP7J2Znll/oIoWf3pa3OJriQwbWAoYpk3U5S+KfONB9qFsnMvan19wUNVdQvCDfGx/Awj0zQSyIqtbtwrktgltsQ1GPJMB/nRlYi0jTG2YchTvvemwkHtiqqDS/FmY7Srz8Q/GMTPB+thQ== 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 May 28, 2023, at 02:54, Yosry Ahmed wrote: >=20 > On Sat, May 27, 2023 at 8:07=E2=80=AFAM Matthew Wilcox = wrote: >>=20 >> 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: >>>>=20 >>>> 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. >>>>=20 >>>> You should have looked at the git history to see why it was created >>>> and who used it. >>>>=20 >>>> Shakeel, Vasily, are you going to retry adding commit 1d0403d20f6c? >>>=20 >>> 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. >>=20 >> The commit immediately preceding it is fc4db90fe71e. >>=20 >> 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. >>=20 >>> 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? >>=20 >> Clearly not. >=20 > I dived deeper into the history on LKML, and you are right: > https://lore.kernel.org/all/Yp4F6n2Ie32re7Ed@qian/ >=20 > 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. Thanks.