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Thu, 5 Nov 2026 11:37:46 +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 VJcRJYpq7GrlcQAAD6G6ig (envelope-from ); Thu, 05 Nov 2026 11:37:46 +0000 Date: Thu, 5 Nov 2026 11:37:45 +0000 From: Pedro Falcato To: Baolin Wang Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, qi.zheng@linux.dev, ayushr@modal.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: synchronize with PTE table reclaim for all folio sizes Message-ID: References: X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: CA7C721FAE X-Spam-Level: X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Flag: NO X-Spamd-Result: default: False [-13.51 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; MIME_TRACE(0.00)[0:+]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Score: -13.51 On Thu, Nov 05, 2026 at 10:56:28AM +0800, Baolin Wang wrote: > Similar to commit 243cf1f67b36 ("mm: memory: fix truncation removing mapped > folios"), the '!pmd_present()' check in page_vma_mapped_walk() can also race > with concurrent page table reclamation via zap_empty_pte_table(). > > page_vma_mapped_walk() is used by many functions including try_to_unmap(), > try_to_migrate(), folio_mkclean(), pfn_mkclean_range(), remove_migration_ptes(), > page_mapped_in_vma(), and mapping_wrprotect_range(). Except for try_to_unmap() > and try_to_migrate(), the other callers do not perform post-walk accounting > checks, so the race has no observable impact on them. > > For migration, the race can cause unnecessary retries. For reclaim via > try_to_unmap(), the race can cause failure to reclaim a folio that is in > fact already unmapped (as shown below), which may lead to unexpected OOM > or increased refaults. This is very handwavy. Do you have numbers? Does this actually make sense? -- Pedro