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Tue, 21 Apr 2026 03:45:46 +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 U/DjEury5ml4VwAAD6G6ig (envelope-from ); Tue, 21 Apr 2026 03:45:46 +0000 Date: Tue, 21 Apr 2026 05:45:40 +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 1/4] mm/sparse-vmemmap: Fix vmemmap accounting underflow Message-ID: References: <20260421022044.1217503-1-songmuchun@bytedance.com> <20260421022044.1217503-2-songmuchun@bytedance.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260421022044.1217503-2-songmuchun@bytedance.com> X-Spam-Score: -4.30 X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; 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]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[19]; FUZZY_RATELIMITED(0.00)[rspamd.com]; 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)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[bytedance.com:email,imap1.dmz-prg2.suse.org:helo,suse.de:email] X-Spam-Flag: NO On Tue, Apr 21, 2026 at 10:20:41AM +0800, Muchun Song wrote: > In section_activate(), if populate_section_memmap() fails, the error > handling path calls section_deactivate() to roll back the state. This > causes a vmemmap accounting imbalance. > > Since commit c3576889d87b ("mm: fix accounting of memmap pages"), > memmap pages are accounted for only after populate_section_memmap() > succeeds. However, the failure path unconditionally calls > section_deactivate(), which decreases the vmemmap count. Consequently, > a failure in populate_section_memmap() leads to an accounting underflow, > incorrectly reducing the system's tracked vmemmap usage. > > Fix this more thoroughly by moving all accounting calls into the lower > level functions that actually perform the vmemmap allocation and freeing: > > - populate_section_memmap() accounts for newly allocated vmemmap pages > - depopulate_section_memmap() unaccounts when vmemmap is freed > > This ensures proper accounting in all code paths, including error > handling and early section cases. > > Fixes: c3576889d87b ("mm: fix accounting of memmap pages") > Signed-off-by: Muchun Song > Acked-by: Mike Rapoport (Microsoft) Acked-by: Oscar Salvador -- Oscar Salvador SUSE Labs