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Wed, 30 Apr 2025 11:15:23 -0700 (PDT) MIME-Version: 1.0 References: <20250430181052.55698-1-ryncsn@gmail.com> <20250430181052.55698-5-ryncsn@gmail.com> In-Reply-To: <20250430181052.55698-5-ryncsn@gmail.com> From: Kairui Song Date: Thu, 1 May 2025 02:15:06 +0800 X-Gm-Features: ATxdqUFkfhYcI-xu2JK_XpeN5Mtxg3WBPHGYn_pVC1uNsqLT6ryrqzsJgPa2fY4 Message-ID: Subject: Re: [PATCH v3 4/6] filemap: do not use folio_contains for swap cache folios To: linux-mm@kvack.org Cc: Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , David Hildenbrand , Yosry Ahmed , "Huang, Ying" , Nhat Pham , Johannes Weiner , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: 68D171C000A X-Rspamd-Server: rspam04 X-Stat-Signature: i4mx6knhkokrghuctmo4cdahe6ngxjsw X-HE-Tag: 1746036926-406472 X-HE-Meta: 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 jIK6Qpbq uACY1YGCVeQ+J+4fKBcS4HBOLqB3kklGeHDldVAtA/5ewqQ0t9NaMvHkZozJyR/tkal86QucAAQ/Pvn0ErKPWD7ofBas//IjuPXX8ZFH54Y9fh47nnCbR2ZqPtbGeKlf315fHUUmOBzMVaHne5nWdAD6bIr18cmfPTLZd8JGCBy2C9rVjyhzM8OYCZ1sRGRtcg6RVu4V/gdIJm+2oXSWejqDr5rfe+kGC7Nh459rborAOz9TEeJEurwm9MV+hKOUOc1wVTj5nVmq1uLitzvKjftFxhnM6CxA/cbL9WQvO/uW2zyXDJA8elin5d8YXiLUGHY5WU3GEsuOOzLsclnSeziTIxTxVXCHSEL1ekvblcJfwRhjgpHVXI3Y67I5M+cQ7Xa1qQnrNyYWLkuWVA6mygcnKGJUswbh/WvggW+ffWAWTvpT2hBaEHG3C3g== 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 Thu, May 1, 2025 at 2:11=E2=80=AFAM Kairui Song wrote= : > > From: Kairui Song > > Currently, none of the folio_contains callers should encounter swap > cache folios. > > For fs/ callers, swap cache folios are never part of their workflow. > > For filemap and truncate, folio_contains is only used for sanity > checks to verify the folio index matches the expected > lookup / invalidation target. > > The swap cache does not utilize filemap or truncate helpers in ways > that would trigger these checks, as it mostly implements its own > cache management. > > Shmem won't trigger these sanity checks either unless thing went > wrong, as it would directly trigger a BUG because swap cache index are > unrelated and almost never matches shmem index. Shmem have to handle > mixed values of folios, shadows, and swap entries, so it has its own > way of handling the mapping. > > While some filemap helpers works for swap cache space, the swap cache > is different from the page cache in many ways. So this particular helper > will unlikely to work in a helpful way for swap cache folios. > > So make it explicit here that folio_contains should not be used for > swap cache folios. This helps to avoid misuse, make swap cache less > exposed and remove the folio_index usage here. > > Signed-off-by: Kairui Song > Acked-by: David Hildenbrand > --- > include/linux/pagemap.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index af25fb640463..0c9aff5ec77f 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -935,14 +935,14 @@ static inline struct page *folio_file_page(struct f= olio *folio, pgoff_t index) > * @folio: The folio. > * @index: The page index within the file. > * > - * Context: The caller should have the page locked in order to prevent > - * (eg) shmem from moving the page between the page cache and swap cache > - * and changing its index in the middle of the operation. > + * Context: The caller should have the folio locked and ensure > + * e.g., shmem did not move this folio to the swap cache. > * Return: true or false. > */ > static inline bool folio_contains(struct folio *folio, pgoff_t index) > { > - return index - folio_index(folio) < folio_nr_pages(folio); > + VM_WARN_ON_FOLIO(folio_test_swapcache(folio), folio); Ah, my bad, it will be better to be VM_WARN_ON_ONCE_FOLIO here as suggested by David, other than this this series should be good. > + return index - folio->index < folio_nr_pages(folio); > } > > unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *star= t, > -- > 2.49.0 >