| Message ID | 20240409192301.907377-7-david@redhat.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | mm: mapcount for large folios + page_mapcount() cleanups | expand |
On 09.04.24 21:22, David Hildenbrand wrote: > We already handle it properly for large folios. Let's also return "0" > for small typed folios, like page_mapcount() currently would. > > Consequently, folio_mapcount() will never return negative values for > typed folios, but may return negative values for underflows. > > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > include/linux/mm.h | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index daf687f0e8e5..d453232bba62 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1260,12 +1260,19 @@ static inline int folio_large_mapcount(const struct folio *folio) > * references the entire folio counts exactly once, even when such special > * page table entries are comprised of multiple ordinary page table entries. > * > + * Will report 0 for pages which cannot be mapped into userspace, such as > + * slab, page tables and similar. > + * > * Return: The number of times this folio is mapped. > */ > static inline int folio_mapcount(const struct folio *folio) > { > - if (likely(!folio_test_large(folio))) > - return atomic_read(&folio->_mapcount) + 1; > + int mapcount; > + > + if (likely(!folio_test_large(folio))) { > + mapcount = atomic_read(&folio->_mapcount); > + return page_type_has_type(mapcount) ? 0 : mapcount + 1; > + } > return folio_large_mapcount(folio); > } > From 98acfb7ff35cb65fcfca5e799bf58f8afe84a645 Mon Sep 17 00:00:00 2001 From: David Hildenbrand <david@redhat.com> Date: Wed, 24 Apr 2024 10:56:17 +0200 Subject: [PATCH] !fixup: mm: make folio_mapcount() return 0 for small typed folios Just like page_mapcount(), let's make folio_mapcount() slightly more efficient. Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/mm.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index cf700c5cdd58b..78e583b50e421 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1271,8 +1271,11 @@ static inline int folio_mapcount(const struct folio *folio) int mapcount; if (likely(!folio_test_large(folio))) { - mapcount = atomic_read(&folio->_mapcount); - return page_type_has_type(mapcount) ? 0 : mapcount + 1; + mapcount = atomic_read(&folio->_mapcount) + 1; + /* Handle page_has_type() pages */ + if (mapcount < PAGE_MAPCOUNT_RESERVE + 1) + mapcount = 0; + return mapcount; } return folio_large_mapcount(folio); }
diff --git a/include/linux/mm.h b/include/linux/mm.h index daf687f0e8e5..d453232bba62 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1260,12 +1260,19 @@ static inline int folio_large_mapcount(const struct folio *folio) * references the entire folio counts exactly once, even when such special * page table entries are comprised of multiple ordinary page table entries. * + * Will report 0 for pages which cannot be mapped into userspace, such as + * slab, page tables and similar. + * * Return: The number of times this folio is mapped. */ static inline int folio_mapcount(const struct folio *folio) { - if (likely(!folio_test_large(folio))) - return atomic_read(&folio->_mapcount) + 1; + int mapcount; + + if (likely(!folio_test_large(folio))) { + mapcount = atomic_read(&folio->_mapcount); + return page_type_has_type(mapcount) ? 0 : mapcount + 1; + } return folio_large_mapcount(folio); }
We already handle it properly for large folios. Let's also return "0" for small typed folios, like page_mapcount() currently would. Consequently, folio_mapcount() will never return negative values for typed folios, but may return negative values for underflows. Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/mm.h | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)