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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vvLxF-00000001e1C-2dOQ; Wed, 25 Feb 2026 20:57:57 +0000 Date: Wed, 25 Feb 2026 20:57:57 +0000 From: Matthew Wilcox To: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , cgroups@vger.kernel.org, linux-mm@kvack.org Cc: Axel Rasmussen Subject: Re: [PATCH 3/3] ptdesc: Account page tables to memcgs again Message-ID: References: <20260225162319.315281-1-willy@infradead.org> <20260225162319.315281-4-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260225162319.315281-4-willy@infradead.org> X-Stat-Signature: opfzffk1o93zqq4hnsz77m1yeo9jrec8 X-Rspamd-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: 56E6B4000D X-HE-Tag: 1772053081-56064 X-HE-Meta: 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 3ZO7Sp0f ZHETK1el42OcuS2sPQT5h3sRIQo+XuOVfwfSjVFGVMQknuSa6jE/MuZVxLljQ7Kf5WTHHtjd5rW/xMIzNnLnxsWUge/FzAhOF3c7GcNvV1qJEDaH+IABYSitpvCKjOWfNk2ILcVBt3WuXMPu7KtxxxhjmNERZNCfxxABgWhVM7sHOt7mEI7SvfJUooDKDeeJ/D0IYhFWYAwetetv7LCxpPw6iFxC8Iwy/pMrL5qPxrb09hsQVgTjpM1Bj9g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Feb 25, 2026 at 04:22:17PM +0000, Matthew Wilcox (Oracle) wrote: > static inline void __pagetable_ctor(struct ptdesc *ptdesc) > { > pg_data_t *pgdat = NODE_DATA(memdesc_nid(ptdesc->pt_flags)); > + struct mem_cgroup *memcg = pagetable_memcg(ptdesc); > > __SetPageTable(ptdesc_page(ptdesc)); > - mod_node_page_state(pgdat, NR_PAGETABLE, ptdesc_nr_pages(ptdesc)); > + memcg_stat_mod(memcg, pgdat, NR_PAGETABLE, ptdesc_nr_pages(ptdesc)); > } It occurs to me that we're not holding the rcu_read_lock() here (whereas we do for the other two callers). I'm not quite clear on what the rcu read lock is protecting here -- can it be that the memcg is rcu-freed while a page table belongs to it? Or does the task existing prevent the memcg from being freed? (is there documentation on this that I've been unable to find?)