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Tue, 29 Apr 2025 06:32:55 -0700 (PDT) MIME-Version: 1.0 References: <20250429114949.41124-1-ryncsn@gmail.com> <20250429114949.41124-5-ryncsn@gmail.com> <116d8920-6154-4ed1-946a-887cfe084fe9@redhat.com> In-Reply-To: <116d8920-6154-4ed1-946a-887cfe084fe9@redhat.com> From: Kairui Song Date: Tue, 29 Apr 2025 21:32:38 +0800 X-Gm-Features: ATxdqUHoUuhpLeU5Fj7rU7y8Azm60EAgkDBT80F_4JUCnHpkDv2oQWGVrihzMIs Message-ID: Subject: Re: [PATCH v2 4/6] filemap: do not use folio_contains for swap cache folios To: David Hildenbrand Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , 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-Rspamd-Queue-Id: 38B311A0011 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: rpaubey1qzdsd4jyhtu7hnurha4f9uh9 X-HE-Tag: 1745933577-618266 X-HE-Meta: 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 wY/q6gCT HpWMCmwefHPITALRh+U/MM6MujR4Tg6qtVeik/dmqCwSXVR5BnggeFpy1epX1U03h7LluBA8gT1u/0K0DgKIsEsMvhiimKMD/Nnw4I0bYP0ClD2D1p3UW2znA5oNZx2AoN1rPrSziiqOgSZhWE2Q/KDWSJ6SD/jsSRSglSBk2/KLgRN6xQZ34nxM235uZit+g+mBceciC5TomJPCQS0ykUkulhfnA4HW0jUNJGWvm+KuBPaOztY7wAFosBZ249KBbSydwFPVSM+B6Gs9HXT/yk0pjz1H64q9SVFowEGNHi4/rbgckofnUECmStAB1Z6qmUDTciSRa/QJMl+LQ8rXYt/RFhWebi9RznJ8RFgQSXlGK8KUW9uYLJDT5irl/6GXKHzawcL2imWDSCL3lLliF+n1MzkQT1F7MKMhW 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, Apr 29, 2025 at 8:22=E2=80=AFPM David Hildenbrand wrote: > > On 29.04.25 13:49, 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 helpe= r > > 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 > > --- > > 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..1dc3416a9c0d 100644 > > --- a/include/linux/pagemap.h > > +++ b/include/linux/pagemap.h > > @@ -935,14 +935,14 @@ static inline struct page *folio_file_page(struct= folio *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 cac= he > > - * 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 swap cache. > > The "(e.g.)" looks weird. Maybe "ensure that e.g., shmem ..." > > "to the" > > > * 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_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); > > Likely you want VM_WARN_ON_ONCE_FOLIO() here. All its caller will trigger a bug if it encounters a swap cache, so I kept that behaviour consistent. Let's keep that unchanged for now. > > > + return index - folio->index < folio_nr_pages(folio); > > } > > > > unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *s= tart, > > > Acked-by: David Hildenbrand Thanks! > > -- > Cheers, > > David / dhildenb > >