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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vvM0U-00000001eGe-2y1H; Wed, 25 Feb 2026 21:01:18 +0000 Date: Wed, 25 Feb 2026 21:01:18 +0000 From: Matthew Wilcox To: Shakeel Butt Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , cgroups@vger.kernel.org, linux-mm@kvack.org, 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: X-Stat-Signature: prxds1ewer1ah4jo4gnpypkd3tpcru1d X-Rspamd-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: AC68340010 X-HE-Tag: 1772053280-784562 X-HE-Meta: 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 CxT7O4hW 4Xh3W7KkzUXRmrjsnQFyVS+qU181DjnVsoXV8HikCd4r/n1fg/Rl3Xy6BIJw5BDJg55TCZI6i/wpMygxOgbZtYRmd865eS9Lh3hOJBZYbAT8sQQZzauR9E7+Guh7JKYHbZ2U/ofC4a4a5EP1VOEVuBG/nvkkGFRdoAVbZJ7o06UOCWwwucAY52NTrNVRLfq9aVOxWL5X6NmWC7EQcxIrTpHU+tzrObawsouCQO3JRAAS7curwLTMVrfq4PA== 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 08:55:54AM -0800, Shakeel Butt wrote: > > #ifdef CONFIG_MEMCG > > - unsigned long pt_memcg_data; > > + struct mem_cgroup *pt_memcg; > > This is kernel memory, so this would be struct obj_cgroup * instead of struct > mem_cgroup pointer. We will need something similar to __folio_objcg(), maybe > __ptdesc_objcg() and then call obj_cgroup_memcg() on it. Basically how > folio_memcg() handles the kernel memory. Why would we want to do that instead of just stashing a pointer to the memcg in the ptdesc? I feel very stupid about the differences between all of these things and would dearly love to read some documentation to learn.