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Thu, 24 Sep 2020 13:07:14 -0700 (PDT) Date: Thu, 24 Sep 2020 16:05:42 -0400 From: Johannes Weiner To: Roman Gushchin Cc: Andrew Morton , Shakeel Butt , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com Subject: Re: [PATCH v1 3/4] mm: introduce page memcg flags Message-ID: <20200924200542.GD329853@cmpxchg.org> References: <20200922203700.2879671-1-guro@fb.com> <20200922203700.2879671-4-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200922203700.2879671-4-guro@fb.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000014, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 22, 2020 at 01:36:59PM -0700, Roman Gushchin wrote: > @@ -422,7 +421,13 @@ static inline void clear_page_mem_cgroup(struct page *page) > */ > static inline struct obj_cgroup **page_obj_cgroups(struct page *page) > { > - return (struct obj_cgroup **)(page->memcg_data & ~0x1UL); > + unsigned long memcg_data = page->memcg_data; > + > + VM_BUG_ON_PAGE(memcg_data && !test_bit(PG_MEMCG_OBJ_CGROUPS, > + &memcg_data), page); > + __clear_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data); > + > + return (struct obj_cgroup **)memcg_data; Slab allocations set up page->memcg_data locklessly, right? AFAICS, the page_objcg lookup functions all need READ_ONCE() loads.