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-rw-r--r--include/linux/page-flags.h22
1 files changed, 22 insertions, 0 deletions
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index f4ed4f1b0c77..6b052aa7b5b7 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -517,6 +517,27 @@ static inline int PageTransCompound(struct page *page)
}
/*
+ * PageTransCompoundMap is the same as PageTransCompound, but it also
+ * guarantees the primary MMU has the entire compound page mapped
+ * through pmd_trans_huge, which in turn guarantees the secondary MMUs
+ * can also map the entire compound page. This allows the secondary
+ * MMUs to call get_user_pages() only once for each compound page and
+ * to immediately map the entire compound page with a single secondary
+ * MMU fault. If there will be a pmd split later, the secondary MMUs
+ * will get an update through the MMU notifier invalidation through
+ * split_huge_pmd().
+ *
+ * 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
+ * positives.
+ */
+static inline int PageTransCompoundMap(struct page *page)
+{
+ return PageTransCompound(page) && atomic_read(&page->_mapcount) < 0;
+}
+
+/*
* PageTransTail returns true for both transparent huge pages
* and hugetlbfs pages, so it should only be called when it's known
* that hugetlbfs pages aren't involved.
@@ -559,6 +580,7 @@ static inline int TestClearPageDoubleMap(struct page *page)
#else
TESTPAGEFLAG_FALSE(TransHuge)
TESTPAGEFLAG_FALSE(TransCompound)
+TESTPAGEFLAG_FALSE(TransCompoundMap)
TESTPAGEFLAG_FALSE(TransTail)
TESTPAGEFLAG_FALSE(DoubleMap)
TESTSETFLAG_FALSE(DoubleMap)