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From: Shakeel Butt To: Yu Zhao Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Hugh Dickins , Yosry Ahmed , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH] memcg: workingset: remove folio_memcg_rcu usage Message-ID: References: <20241026071145.3287517-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: m7ujzyqgk38jkwqax58q51s5shf7at66 X-Rspamd-Queue-Id: EA0EC4001C X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1729960460-938650 X-HE-Meta: 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 lPduO+pa BhZgZW4SKzY/aCcSMDwEEuZxgTOAFiF7vC/Z7QA1fNUIB2Y1atmg0+1qJMteez4qhcm4tJyEHDbwEvj12gknr+1J52TeSAXNbyursG84NitEc1YDxYvLKxdnjQ4dsPlrHv8kFr5C3zydywtFJlnetMe7csv/VmSXjQyYfTOEynrS/c+gql0gBUAUul4AuR+0sxcmUPU8c0RWfYNliR91MFHezoDM9SQ735gceHA3ZWM3pw1PJ8yzUTBgSDg== 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: List-Subscribe: List-Unsubscribe: On Sat, Oct 26, 2024 at 09:37:00AM GMT, Yu Zhao wrote: > On Sat, Oct 26, 2024 at 1:12 AM Shakeel Butt wrote: > > > > The function workingset_activation() is called from > > folio_mark_accessed() with the guarantee that the given folio can not be > > freed under us in workingset_activation(). In addition, the association > > of the folio and its memcg can not be broken here because charge > > migration is no more. There is no need to use folio_memcg_rcu. Simply > > use folio_memcg_charged() because that is what this function cares > > about. > > > > Signed-off-by: Shakeel Butt > > Suggested-by: Yu Zhao > > --- > > > > Andrew, please put this patch after the charge migration deprecation > > series. > > > > include/linux/memcontrol.h | 35 ----------------------------------- > > mm/workingset.c | 10 ++-------- > > 2 files changed, 2 insertions(+), 43 deletions(-) > > > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > > index 932534291ca2..89a1e9f10e1b 100644 > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -443,35 +443,6 @@ static inline bool folio_memcg_charged(struct folio *folio) > > return __folio_memcg(folio) != NULL; > > } > > > > -/** > > - * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio. > > - * @folio: Pointer to the folio. > > - * > > - * This function assumes that the folio is known to have a > > - * proper memory cgroup pointer. It's not safe to call this function > > - * against some type of folios, e.g. slab folios or ex-slab folios. > > - * > > - * Return: A pointer to the memory cgroup associated with the folio, > > - * or NULL. > > - */ > > -static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio) > > -{ > > - unsigned long memcg_data = READ_ONCE(folio->memcg_data); > > - > > - VM_BUG_ON_FOLIO(folio_test_slab(folio), folio); > > - > > - if (memcg_data & MEMCG_DATA_KMEM) { > > - struct obj_cgroup *objcg; > > - > > - objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK); > > - return obj_cgroup_memcg(objcg); > > - } > > - > > - WARN_ON_ONCE(!rcu_read_lock_held()); > > - > > - return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK); > > -} > > - > > /* > > * folio_memcg_check - Get the memory cgroup associated with a folio. > > * @folio: Pointer to the folio. > > @@ -1084,12 +1055,6 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio) > > return NULL; > > } > > > > -static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio) > > -{ > > - WARN_ON_ONCE(!rcu_read_lock_held()); > > - return NULL; > > -} > > - > > static inline struct mem_cgroup *folio_memcg_check(struct folio *folio) > > { > > return NULL; > > diff --git a/mm/workingset.c b/mm/workingset.c > > index 4b58ef535a17..c47aa482fad5 100644 > > --- a/mm/workingset.c > > +++ b/mm/workingset.c > > @@ -591,9 +591,6 @@ void workingset_refault(struct folio *folio, void *shadow) > > */ > > void workingset_activation(struct folio *folio) > > { > > - struct mem_cgroup *memcg; > > - > > - rcu_read_lock(); > > /* > > * Filter non-memcg pages here, e.g. unmap can call > > * mark_page_accessed() on VDSO pages. > > @@ -601,12 +598,9 @@ void workingset_activation(struct folio *folio) > > * XXX: See workingset_refault() - this should return > > * root_mem_cgroup even for !CONFIG_MEMCG. > > The "XXX" part of the comments doesn't apply anymore. > > > */ > > - memcg = folio_memcg_rcu(folio); > > - if (!mem_cgroup_disabled() && !memcg) > > - goto out; > > + if (mem_cgroup_disabled() || !folio_memcg_charged(folio)) > > + return; > > workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio)); > > if (mem_cgroup_disabled() || folio_memcg_charged(folio)) > workingset_age_nonresident() > > We still want to call workingset_age_nonresident() when memcg is > disabled. (We just want to "Filter non-memcg pages here" when memcg is > enabled, as the comment above says, which I assume still applies?) > Yes, you are right. Let me send the v2 with the fix.