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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> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260421022044.1217503-4-songmuchun@bytedance.com> X-Spamd-Result: default: False [-8.30 / 50.00]; REPLY(-4.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[19]; MISSING_XM_UA(0.00)[]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[linux-foundation.org,kernel.org,linux.dev,ellerman.id.au,linux.ibm.com,oracle.com,google.com,suse.com,gmail.com,kvack.org,lists.ozlabs.org,vger.kernel.org]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,localhost.localdomain:mid,suse.de:email] 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