[{"id":3679662,"web_url":"http://patchwork.ozlabs.org/comment/3679662/","msgid":"","date":"2026-04-21T04:00:19","subject":"Re: [PATCH v3 3/4] mm/sparse-vmemmap: Fix DAX vmemmap accounting\n with optimization","submitter":{"id":76330,"url":"http://patchwork.ozlabs.org/api/people/76330/","name":"Oscar Salvador","email":"osalvador@suse.de"},"content":"On Tue, Apr 21, 2026 at 10:20:43AM +0800, Muchun Song wrote:\n> When vmemmap optimization is enabled for DAX, the nr_memmap_pages\n> counter in /proc/vmstat is incorrect. The current code always accounts\n> for the full, non-optimized vmemmap size, but vmemmap optimization\n> reduces the actual number of vmemmap pages by reusing tail pages. This\n> causes the system to overcount vmemmap usage, leading to inaccurate\n> page statistics in /proc/vmstat.\n> \n> Fix this by introducing section_vmemmap_pages(), which returns the exact\n> vmemmap page count for a given pfn range based on whether optimization\n> is in effect.\n> \n> Fixes: 15995a352474 (\"mm: report per-page metadata information\")\n> Signed-off-by: Muchun Song \n> Acked-by: Mike Rapoport (Microsoft) \n\nAcked-by: Oscar Salvador ","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256\n header.s=susede2_rsa header.b=l/rWzc7W;\n\tdkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256\n header.s=susede2_ed25519 header.b=qkBNhF1f;\n\tdkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de\n header.a=rsa-sha256 header.s=susede2_rsa header.b=l/rWzc7W;\n\tdkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256\n header.s=susede2_ed25519 header.b=qkBNhF1f;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; 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Howlett\" ,\n\tVlastimil Babka ,\n\tSuren Baghdasaryan ,\n\tMichal Hocko , Nicholas Piggin ,\n\tChristophe Leroy , aneesh.kumar@linux.ibm.com,\n\tjoao.m.martins@oracle.com, linux-mm@kvack.org,\n\tlinuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org","Subject":"Re: [PATCH v3 3/4] mm/sparse-vmemmap: Fix DAX vmemmap accounting\n with optimization","Message-ID":"","References":"<20260421022044.1217503-1-songmuchun@bytedance.com>\n <20260421022044.1217503-4-songmuchun@bytedance.com>","X-Mailing-List":"linuxppc-dev@lists.ozlabs.org","List-Id":"","List-Help":"","List-Owner":"","List-Post":"","List-Archive":",\n ","List-Subscribe":",\n ,\n ","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-Spam-Score":"-8.30","X-Spam-Level":"","X-Spamd-Result":"default: False [-8.30 / 50.00];\n\tREPLY(-4.00)[];\n\tBAYES_HAM(-3.00)[100.00%];\n\tNEURAL_HAM_LONG(-1.00)[-1.000];\n\tNEURAL_HAM_SHORT(-0.20)[-1.000];\n\tMIME_GOOD(-0.10)[text/plain];\n\tFUZZY_RATELIMITED(0.00)[rspamd.com];\n\tRCVD_VIA_SMTP_AUTH(0.00)[];\n\tMIME_TRACE(0.00)[0:+];\n\tRCPT_COUNT_TWELVE(0.00)[19];\n\tMISSING_XM_UA(0.00)[];\n\tARC_NA(0.00)[];\n\tRCVD_TLS_ALL(0.00)[];\n\tFREEMAIL_ENVRCPT(0.00)[gmail.com];\n\tDKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519];\n\tFROM_HAS_DN(0.00)[];\n\tFREEMAIL_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];\n\tTO_DN_SOME(0.00)[];\n\tFROM_EQ_ENVFROM(0.00)[];\n\tRCVD_COUNT_TWO(0.00)[2];\n\tTO_MATCH_ENVRCPT_ALL(0.00)[];\n\tDBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,localhost.localdomain:mid,suse.de:email]","X-Spam-Status":"No, score=-0.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID,\n\tDKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS autolearn=disabled\n\tversion=4.0.1 OzLabs 8","X-Spam-Checker-Version":"SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org"}}]