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From: Roman Gushchin To: Yafang Shao Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, quentin@isovalent.com, hannes@cmpxchg.org, mhocko@kernel.org, shakeelb@google.com, songmuchun@bytedance.com, akpm@linux-foundation.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz, linux-mm@kvack.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH bpf-next 03/10] mm, memcg: Add new helper obj_cgroup_from_current() Message-ID: References: <20220619155032.32515-1-laoar.shao@gmail.com> <20220619155032.32515-4-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220619155032.32515-4-laoar.shao@gmail.com> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655953286; a=rsa-sha256; cv=none; b=uqSS078QxOcjz/FtQAWJiI7K6z9Y/U3doGkJxHFPRGhFwEzmbnXPzIFTjg/t7nbpjbIuMx j9eAZL9Q/vyMIcjS12Woar5q8Se8H4axYdwy44MSnbvh7TWE/AZbXEOsen3LCwHdVme1EF yELFrrRa+l2sYaidm3JKwgOFKNTa/Xg= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KMRiFv2V; spf=pass (imf17.hostedemail.com: domain of roman.gushchin@linux.dev designates 94.23.1.103 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655953286; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=n5GDjc2kkjgyMykxueFJ5rZ4OEDMKe2lQ0sdlnoaP7g=; b=Hgldk2i+UR6XsgqsHagw+j/dsJU5U4KDng29bQ6wAwm4ernYFX6xH9EQAOQIJH5a4L4myP 5WCvaL9cTmtqWA7YlQu8QTVQKaPD3wxaAGd+54b0mJXVmepjEgSOJ3YcKQwHiOKg3IhjI3 iDk16ge2gOke7VQTIsAAE6uQ+smyfek= Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KMRiFv2V; spf=pass (imf17.hostedemail.com: domain of roman.gushchin@linux.dev designates 94.23.1.103 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9583340017 X-Stat-Signature: fd3mauwc41psfonfz6k118rn6uihynm9 X-Rspam-User: X-HE-Tag: 1655953286-404412 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, Jun 19, 2022 at 03:50:25PM +0000, Yafang Shao wrote: > The difference between get_obj_cgroup_from_current() and obj_cgroup_from_current() > is that the later one doesn't add objcg's refcnt. > > Signed-off-by: Yafang Shao > --- > include/linux/memcontrol.h | 1 + > mm/memcontrol.c | 24 ++++++++++++++++++++++++ > 2 files changed, 25 insertions(+) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index cf074156c6ac..402b42670bcd 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -1703,6 +1703,7 @@ bool mem_cgroup_kmem_disabled(void); > int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order); > void __memcg_kmem_uncharge_page(struct page *page, int order); > > +struct obj_cgroup *obj_cgroup_from_current(void); > struct obj_cgroup *get_obj_cgroup_from_current(void); > struct obj_cgroup *get_obj_cgroup_from_page(struct page *page); > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index abec50f31fe6..350a7849dac3 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2950,6 +2950,30 @@ struct obj_cgroup *get_obj_cgroup_from_page(struct page *page) > return objcg; > } > > +__always_inline struct obj_cgroup *obj_cgroup_from_current(void) > +{ > + struct obj_cgroup *objcg = NULL; > + struct mem_cgroup *memcg; > + > + if (memcg_kmem_bypass()) > + return NULL; > + > + rcu_read_lock(); > + if (unlikely(active_memcg())) > + memcg = active_memcg(); > + else > + memcg = mem_cgroup_from_task(current); > + > + for (; memcg != root_mem_cgroup; memcg = parent_mem_cgroup(memcg)) { > + objcg = rcu_dereference(memcg->objcg); > + if (objcg) > + break; > + } > + rcu_read_unlock(); Hm, what prevents the objcg from being released here? Under which conditions it's safe to call it?