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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Miaohe Lin , Naoya Horiguchi , Wei Yang , Balbir Singh , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/4] mm/huge_memory: change folio_split_supported() to folio_check_splittable() Message-Id: <20251125094446.c78c5139f00ad8e00e9bd5d9@linux-foundation.org> In-Reply-To: References: <20251122025529.1562592-1-ziy@nvidia.com> <20251122025529.1562592-2-ziy@nvidia.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 67DE74001F X-Stat-Signature: nmps7gsnaz37zoq3emp31fs4iuejadfc X-Rspam-User: X-HE-Tag: 1764092702-552827 X-HE-Meta: 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 wEmkbpou kTAAcO3DOp/cTv7GzSu4SYNBt9QrShDJl/X9x90djVjy4Gst7DSJEhiN542g4ZzqbORqJf0gD7UJU2ctbk7K5qRcJmM4QqhxXZtiGAW/9aYG10J4= 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, 25 Nov 2025 09:58:03 +0100 "David Hildenbrand (Red Hat)" wrote: > > + * Return: 0 - @folio can be split to @new_order, otherwise an error number is > > + * returned. > > + */ > > +int folio_check_splittable(struct folio *folio, unsigned int new_order, > > + enum split_type split_type, bool warns) > > { > > + VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); > > + /* > > + * Folios that just got truncated cannot get split. Signal to the > > + * caller that there was a race. > > + * > > + * TODO: this will also currently refuse shmem folios that are in the > > + * swapcache. > > + */ > > Per the other discussion, should this even be: > > "this will also currently refuse folios without a mapping in the > swapcache (shmem or to-be-anon folios)" > > IOW, to spell out that anon folios that were read into the swapcache but > not mapped yet into page tables (where we set folio->mapping). This? --- a/mm/huge_memory.c~mm-huge_memory-change-folio_split_supported-to-folio_check_splittable-fix +++ a/mm/huge_memory.c @@ -3714,7 +3714,8 @@ int folio_check_splittable(struct folio * caller that there was a race. * * TODO: this will also currently refuse shmem folios that are in the - * swapcache. + * swapcache. Currently it will also refuse folios without a mapping + * in the swapcache (shmem or to-be-anon folios). */ if (!folio_test_anon(folio) && !folio->mapping) return -EBUSY; _