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Wed, 25 Jun 2025 08:32:41 +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 QkyABSm0W2jmHwAAD6G6ig (envelope-from ); Wed, 25 Jun 2025 08:32:41 +0000 Date: Wed, 25 Jun 2025 10:32:31 +0200 From: Oscar Salvador To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, Andrew Morton , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Dan Williams , Alistair Popple , Matthew Wilcox , Jan Kara , Alexander Viro , Christian Brauner , Zi Yan , Baolin Wang , Lorenzo Stoakes , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato Subject: Re: [PATCH RFC 08/14] mm/huge_memory: mark PMD mappings of the huge zero folio special Message-ID: References: <20250617154345.2494405-1-david@redhat.com> <20250617154345.2494405-9-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250617154345.2494405-9-david@redhat.com> X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0807614000E X-Stat-Signature: kos4pkjijdf64tquc14gwe5cxgh4mryj X-HE-Tag: 1750840363-588407 X-HE-Meta: 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 B3M5HHwa 7ImzB7qd/JwuH69znwvdVMrJzWXk9dYKySim6w/JS9os4lB0rcvl34sioIns1oEFBiNQ2EqxZ33rWk6Th4CIx5454sIcdM032Ma+6ZJQCotvMdOFHtUBO5ApElSnSCnDCo+LR8Fc3JIYP0OakcxzAoRmM0T8Pl9lGc22E5WlhdX9OXOv2pmi3FwJEox/P2fDR7wqNx78Z1eNWiCrUh5KjaY3suTSUSHLxGHVyb6/WFDmfo/gQ8ZfG98V7IwEbAtJQd8uc+18BsCHahZAS6uTrziz5yKdvYbNn2wlwINSgjz44RlRDs/J6C/Lo4azf8hsYcSG8xj7bIdhBBoE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 17, 2025 at 05:43:39PM +0200, David Hildenbrand wrote: > The huge zero folio is refcounted (+mapcounted -- is that a word?) > differently than "normal" folios, similarly (but different) to the ordinary > shared zeropage. > > For this reason, we special-case these pages in > vm_normal_page*/vm_normal_folio*, and only allow selected callers to > still use them (e.g., GUP can still take a reference on them). > > vm_normal_page_pmd() already filters out the huge zero folio. However, > so far we are not marking it as special like we do with the ordinary > shared zeropage. Let's mark it as special, so we can further refactor > vm_normal_page_pmd() and vm_normal_page(). > > While at it, update the doc regarding the shared zero folios. > > Signed-off-by: David Hildenbrand Reviewed-by: Oscar Salvador While doing this, would it make sense to update vm_normal_page_pmd() comments to refelect that pmd_special will also catch huge_zero_folio()? It only mentions huge pfnmaps. It might not be worth doing since you remove that code later on, but maybe if someone stares at this commit alone.. -- Oscar Salvador SUSE Labs