diff options
| author | David Hildenbrand <david@redhat.com> | 2024-07-31 18:07:58 +0200 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-09-02 05:25:57 +0200 |
| commit | 17d5f38b33b66210c5a46af639c47fddfe1c5b4d (patch) | |
| tree | 5060c5271442dbd25aa1724906ca7d0cf7dbda55 /include | |
| parent | mm/rmap: cleanup partially-mapped handling in __folio_remove_rmap() (diff) | |
| download | linux-17d5f38b33b66210c5a46af639c47fddfe1c5b4d.tar.xz linux-17d5f38b33b66210c5a46af639c47fddfe1c5b4d.zip | |
mm: clarify folio_likely_mapped_shared() documentation for KSM folios
For KSM folios, the function actually does what it is supposed to do: even
having multiple mappings inside the same MM is considered "sharing", as
there is no real relationship between these KSM page mappings -- in
contrast to mapping the same file range twice and having the same
pagecache page mapped twice.
Link: https://lkml.kernel.org/r/20240731160758.808925-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/mm.h | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index bd219ac9c026..2f6c08b53e4f 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2132,14 +2132,19 @@ static inline size_t folio_size(const struct folio *folio) * MM ("mapped shared"), or if the folio is only mapped into a single MM * ("mapped exclusively"). * + * For KSM folios, this function also returns "mapped shared" when a folio is + * mapped multiple times into the same MM, because the individual page mappings + * are independent. + * * As precise information is not easily available for all folios, this function * estimates the number of MMs ("sharers") that are currently mapping a folio * using the number of times the first page of the folio is currently mapped * into page tables. * - * For small anonymous folios (except KSM folios) and anonymous hugetlb folios, - * the return value will be exactly correct, because they can only be mapped - * at most once into an MM, and they cannot be partially mapped. + * For small anonymous folios and anonymous hugetlb folios, the return + * value will be exactly correct: non-KSM folios can only be mapped at most once + * into an MM, and they cannot be partially mapped. KSM folios are + * considered shared even if mapped multiple times into the same MM. * * For other folios, the result can be fuzzy: * #. For partially-mappable large folios (THP), the return value can wrongly @@ -2148,9 +2153,6 @@ static inline size_t folio_size(const struct folio *folio) * #. For pagecache folios (including hugetlb), the return value can wrongly * indicate "mapped shared" (false positive) when two VMAs in the same MM * cover the same file range. - * #. For (small) KSM folios, the return value can wrongly indicate "mapped - * shared" (false positive), when the folio is mapped multiple times into - * the same MM. * * Further, this function only considers current page table mappings that * are tracked using the folio mapcount(s). |