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-rw-r--r--include/linux/page-flags.h20
1 files changed, 18 insertions, 2 deletions
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index f91cb8898ff0..1bf83c8fcaa7 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -622,12 +622,28 @@ static inline int PageTransCompound(struct page *page)
*
* Unlike PageTransCompound, this is safe to be called only while
* split_huge_pmd() cannot run from under us, like if protected by the
- * MMU notifier, otherwise it may result in page->_mapcount < 0 false
+ * MMU notifier, otherwise it may result in page->_mapcount check false
* positives.
+ *
+ * We have to treat page cache THP differently since every subpage of it
+ * would get _mapcount inc'ed once it is PMD mapped. But, it may be PTE
+ * mapped in the current process so comparing subpage's _mapcount to
+ * compound_mapcount to filter out PTE mapped case.
*/
static inline int PageTransCompoundMap(struct page *page)
{
- return PageTransCompound(page) && atomic_read(&page->_mapcount) < 0;
+ struct page *head;
+
+ if (!PageTransCompound(page))
+ return 0;
+
+ if (PageAnon(page))
+ return atomic_read(&page->_mapcount) < 0;
+
+ head = compound_head(page);
+ /* File THP is PMD mapped and not PTE mapped */
+ return atomic_read(&page->_mapcount) ==
+ atomic_read(compound_mapcount_ptr(head));
}
/*