thp: alter compound get_page/put_page

[android-x86/kernel.git] / mm / swap.c

diff --git a/mm/swap.c b/mm/swap.c
index 3f48542..33f5292 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -56,17 +56,93 @@ static void __page_cache_release(struct page *page)
                del_page_from_lru(zone, page);
                spin_unlock_irqrestore(&zone->lru_lock, flags);
        }
+}
+
+static void __put_single_page(struct page *page)
+{
+       __page_cache_release(page);
        free_hot_cold_page(page, 0);
 }
 
-static void put_compound_page(struct page *page)
+static void __put_compound_page(struct page *page)
 {
-       page = compound_head(page);
-       if (put_page_testzero(page)) {
-               compound_page_dtor *dtor;
+       compound_page_dtor *dtor;
+
+       __page_cache_release(page);
+       dtor = get_compound_page_dtor(page);
+       (*dtor)(page);
+}
 
-               dtor = get_compound_page_dtor(page);
-               (*dtor)(page);
+static void put_compound_page(struct page *page)
+{
+       if (unlikely(PageTail(page))) {
+               /* __split_huge_page_refcount can run under us */
+               struct page *page_head = page->first_page;
+               smp_rmb();
+               /*
+                * If PageTail is still set after smp_rmb() we can be sure
+                * that the page->first_page we read wasn't a dangling pointer.
+                * See __split_huge_page_refcount() smp_wmb().
+                */
+               if (likely(PageTail(page) && get_page_unless_zero(page_head))) {
+                       unsigned long flags;
+                       /*
+                        * Verify that our page_head wasn't converted
+                        * to a a regular page before we got a
+                        * reference on it.
+                        */
+                       if (unlikely(!PageHead(page_head))) {
+                               /* PageHead is cleared after PageTail */
+                               smp_rmb();
+                               VM_BUG_ON(PageTail(page));
+                               goto out_put_head;
+                       }
+                       /*
+                        * Only run compound_lock on a valid PageHead,
+                        * after having it pinned with
+                        * get_page_unless_zero() above.
+                        */
+                       smp_mb();
+                       /* page_head wasn't a dangling pointer */
+                       flags = compound_lock_irqsave(page_head);
+                       if (unlikely(!PageTail(page))) {
+                               /* __split_huge_page_refcount run before us */
+                               compound_unlock_irqrestore(page_head, flags);
+                               VM_BUG_ON(PageHead(page_head));
+                       out_put_head:
+                               if (put_page_testzero(page_head))
+                                       __put_single_page(page_head);
+                       out_put_single:
+                               if (put_page_testzero(page))
+                                       __put_single_page(page);
+                               return;
+                       }
+                       VM_BUG_ON(page_head != page->first_page);
+                       /*
+                        * We can release the refcount taken by
+                        * get_page_unless_zero now that
+                        * split_huge_page_refcount is blocked on the
+                        * compound_lock.
+                        */
+                       if (put_page_testzero(page_head))
+                               VM_BUG_ON(1);
+                       /* __split_huge_page_refcount will wait now */
+                       VM_BUG_ON(atomic_read(&page->_count) <= 0);
+                       atomic_dec(&page->_count);
+                       VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
+                       compound_unlock_irqrestore(page_head, flags);
+                       if (put_page_testzero(page_head))
+                               __put_compound_page(page_head);
+               } else {
+                       /* page_head is a dangling pointer */
+                       VM_BUG_ON(PageTail(page));
+                       goto out_put_single;
+               }
+       } else if (put_page_testzero(page)) {
+               if (PageHead(page))
+                       __put_compound_page(page);
+               else
+                       __put_single_page(page);
        }
 }
 
@@ -75,7 +151,7 @@ void put_page(struct page *page)
        if (unlikely(PageCompound(page)))
                put_compound_page(page);
        else if (put_page_testzero(page))
-               __page_cache_release(page);
+               __put_single_page(page);
 }
 EXPORT_SYMBOL(put_page);