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 J2u15Rrx Eew81QSKtt5+zqUoXQZXqISaTce1FfwpZ7KQNnZci8mlhVtPD7+sbKAq6ZEdBt+LGJ09Bw7JNKvU2lCdFX5EDRz3mheCZ5H5J9s/RS9H6pA+xNaC9KOY9X9guXXYsehK94zGPFLYIwlZqhjzJI4ZJc7bdDSbE8fIwUwFD 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, Jul 08, 2025 at 10:07:26AM +0200, David Hildenbrand wrote: > > if (folio_test_anon(folio)) { > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > > index 970600d79dac..00ba2c8b221e 100644 > > --- a/include/linux/page-flags.h > > +++ b/include/linux/page-flags.h > > @@ -706,12 +706,15 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted) > > * address_space which maps the folio from disk; whereas "folio_mapped" > > * refers to user virtual address space into which the folio is mapped. > > * > > - * For slab pages, since slab reuses the bits in struct page to store its > > - * internal states, the folio->mapping does not exist as such, nor do > > - * these flags below. So in order to avoid testing non-existent bits, > > - * please make sure that folio_test_slab(folio) actually evaluates to > > - * false before calling the following functions (e.g., folio_test_anon). > > - * See mm/slab.h. > > + * For certain typed pages like slabs, since they reuse bits in struct page > > + * to store internal states, folio->mapping does not point to a valid > > + * mapping, nor do these flags exist. To avoid testing non-existent bits, > > + * make sure folio_has_mapcount() actually evaluates to true before calling > > + * the following functions (e.g., folio_test_anon). > > + * > > + * The folio_has_mapcount() check can be skipped if the folio is mapped > > + * to userspace, since a folio with !folio_has_mapcount() cannot be mapped > > + * to userspace at all. > > */ > > #define FOLIO_MAPPING_ANON 0x1 > > #define FOLIO_MAPPING_ANON_KSM 0x2 > > @@ -1092,6 +1095,11 @@ static inline bool PageHuge(const struct page *page) > > return folio_test_hugetlb(page_folio(page)); > > } > > +static inline bool folio_has_mapcount(const struct folio *folio) > > +{ > > + return !page_has_type(&folio->page) || folio_test_hugetlb(folio); > > +} > > + > > I don't like the naming. I don't like it either, but I couldn't come up with a better name :( > The thing is, in the future only folios will have a mapcount. Agreed. > Asking whether a folio has a mapcount is asking the wrong question. Agreed. > It's rather, that we want to reject *pages* early, and not cast them to the > folio in the first place. Totally agreed. But that's the future, and we're not there yet. What should we do now? -- Cheers, Harry / Hyeonggon