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Tue, 21 Apr 2026 04:00:28 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id CS6oNlz25mnwYwAAD6G6ig (envelope-from ); Tue, 21 Apr 2026 04:00:28 +0000 Date: Tue, 21 Apr 2026 06:00:19 +0200 From: Oscar Salvador To: Muchun Song Cc: Andrew Morton , David Hildenbrand , Muchun Song , Michael Ellerman , Madhavan Srinivasan , Mike Rapoport , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Nicholas Piggin , Christophe Leroy , aneesh.kumar@linux.ibm.com, joao.m.martins@oracle.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 3/4] mm/sparse-vmemmap: Fix DAX vmemmap accounting with optimization Message-ID: References: <20260421022044.1217503-1-songmuchun@bytedance.com> <20260421022044.1217503-4-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260421022044.1217503-4-songmuchun@bytedance.com> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 69333A0011 X-Stat-Signature: c9rdsjnyseeeh5zuccatn6cd83ktg4mf X-Rspam-User: X-HE-Tag: 1776744031-12498 X-HE-Meta: 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 LjMZy24v R9S5ggctAn6uTtEM26XfG3Rvf9mhsSkucHb5R/D8ow9g9i02mZbA2dqQy3kLED8306sWLt6c23ohPgXSdM36mJ2vxE6ORFOxSkE02vsXVsa2QPtSLvXBlDnoDhjr/IC7ZcInpkyhHCAApLkEKrawidOs4QfrW6srO1Ewsm+44U/e0ZcxndiBlwWB0a5SYHX3sZqlfc4uXSQS3oHC4XkTR/Vi37tNMfCdkfuQyAJy/kSygFcDKIIkmD9Gg10JT1W5XZT+WQWiHglnkPyYcYWQrSpBi0MJRN6EDmD9Jxz5f+gUXFdhNcoQVqRgGjQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 21, 2026 at 10:20:43AM +0800, Muchun Song wrote: > When vmemmap optimization is enabled for DAX, the nr_memmap_pages > counter in /proc/vmstat is incorrect. The current code always accounts > for the full, non-optimized vmemmap size, but vmemmap optimization > reduces the actual number of vmemmap pages by reusing tail pages. This > causes the system to overcount vmemmap usage, leading to inaccurate > page statistics in /proc/vmstat. > > Fix this by introducing section_vmemmap_pages(), which returns the exact > vmemmap page count for a given pfn range based on whether optimization > is in effect. > > Fixes: 15995a352474 ("mm: report per-page metadata information") > Signed-off-by: Muchun Song > Acked-by: Mike Rapoport (Microsoft) Acked-by: Oscar Salvador -- Oscar Salvador SUSE Labs