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 (file)
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -126,6 +126,23 @@ static inline int hpage_nr_pages(struct page *page)
                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 @@ static inline int split_huge_page(struct page *page)
        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 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -415,20 +415,11 @@ out:
 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 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -104,34 +104,24 @@ static pfn_t fault_pfn;
 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);
        }