thp: add compound_trans_head() helper
Cleanup some code with common compound_trans_head helper.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index bddfba1..8e6c8c4 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -126,6 +126,23 @@
return HPAGE_PMD_NR;
return 1;
}
+static inline struct page *compound_trans_head(struct page *page)
+{
+ if (PageTail(page)) {
+ struct page *head;
+ head = page->first_page;
+ smp_rmb();
+ /*
+ * head may be a dangling pointer.
+ * __split_huge_page_refcount clears PageTail before
+ * overwriting first_page, so if PageTail is still
+ * there it means the head pointer isn't dangling.
+ */
+ if (PageTail(page))
+ return head;
+ }
+ return page;
+}
#else /* CONFIG_TRANSPARENT_HUGEPAGE */
#define HPAGE_PMD_SHIFT ({ BUG(); 0; })
#define HPAGE_PMD_MASK ({ BUG(); 0; })
@@ -144,6 +161,7 @@
do { } while (0)
#define wait_split_huge_page(__anon_vma, __pmd) \
do { } while (0)
+#define compound_trans_head(page) compound_head(page)
static inline int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
{
diff --git a/mm/ksm.c b/mm/ksm.c
index 4d5a681..33781de 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -415,20 +415,11 @@
static struct page *page_trans_compound_anon(struct page *page)
{
if (PageTransCompound(page)) {
- struct page *head;
- head = compound_head(page);
+ struct page *head = compound_trans_head(page);
/*
- * head may be a dangling pointer.
- * __split_huge_page_refcount clears PageTail
- * before overwriting first_page, so if
- * PageTail is still there it means the head
- * pointer isn't dangling.
+ * head may actually be splitted and freed from under
+ * us but it's ok here.
*/
- if (head != page) {
- smp_rmb();
- if (!PageTransCompound(page))
- return NULL;
- }
if (PageAnon(head))
return head;
}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4286d47..f29abeb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -104,34 +104,24 @@
inline int kvm_is_mmio_pfn(pfn_t pfn)
{
if (pfn_valid(pfn)) {
- struct page *head;
+ int reserved;
struct page *tail = pfn_to_page(pfn);
- head = compound_head(tail);
+ struct page *head = compound_trans_head(tail);
+ reserved = PageReserved(head);
if (head != tail) {
- smp_rmb();
/*
- * head may be a dangling pointer.
- * __split_huge_page_refcount clears PageTail
- * before overwriting first_page, so if
- * PageTail is still there it means the head
- * pointer isn't dangling.
+ * "head" is not a dangling pointer
+ * (compound_trans_head takes care of that)
+ * but the hugepage may have been splitted
+ * from under us (and we may not hold a
+ * reference count on the head page so it can
+ * be reused before we run PageReferenced), so
+ * we've to check PageTail before returning
+ * what we just read.
*/
- if (PageTail(tail)) {
- /*
- * the "head" is not a dangling
- * pointer but the hugepage may have
- * been splitted from under us (and we
- * may not hold a reference count on
- * the head page so it can be reused
- * before we run PageReferenced), so
- * we've to recheck PageTail before
- * returning what we just read.
- */
- int reserved = PageReserved(head);
- smp_rmb();
- if (PageTail(tail))
- return reserved;
- }
+ smp_rmb();
+ if (PageTail(tail))
+ return reserved;
}
return PageReserved(tail);
}