1 files changed, 82 insertions, 61 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 5ae6b8b78c80..6d1daeb1cb4a 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -67,10 +67,10 @@ void show_swap_cache_info(void)
 }
 
 /*
- * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
+ * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  * but sets SwapCache flag and private instead of mapping and index.
  */
-int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
+static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 {
         int error;
 
@@ -78,28 +78,43 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
         VM_BUG_ON(PageSwapCache(page));
         VM_BUG_ON(!PageSwapBacked(page));
 
+        page_cache_get(page);
+        SetPageSwapCache(page);
+        set_page_private(page, entry.val);
+
+        spin_lock_irq(&swapper_space.tree_lock);
+        error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
+        if (likely(!error)) {
+                total_swapcache_pages++;
+                __inc_zone_page_state(page, NR_FILE_PAGES);
+                INC_CACHE_INFO(add_total);
+        }
+        spin_unlock_irq(&swapper_space.tree_lock);
+
+        if (unlikely(error)) {
+                /*
+                 * Only the context which have set SWAP_HAS_CACHE flag
+                 * would call add_to_swap_cache().
+                 * So add_to_swap_cache() doesn't returns -EEXIST.
+                 */
+                VM_BUG_ON(error == -EEXIST);
+                set_page_private(page, 0UL);
+                ClearPageSwapCache(page);
+                page_cache_release(page);
+        }
+
+        return error;
+}
+
+
+int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
+{
+        int error;
+
         error = radix_tree_preload(gfp_mask);
         if (!error) {
-                page_cache_get(page);
-                SetPageSwapCache(page);
-                set_page_private(page, entry.val);
-
-                spin_lock_irq(&swapper_space.tree_lock);
-                error = radix_tree_insert(&swapper_space.page_tree,
-                                                entry.val, page);
-                if (likely(!error)) {
-                        total_swapcache_pages++;
-                        __inc_zone_page_state(page, NR_FILE_PAGES);
-                        INC_CACHE_INFO(add_total);
-                }
-                spin_unlock_irq(&swapper_space.tree_lock);
+                error = __add_to_swap_cache(page, entry);
                 radix_tree_preload_end();
-
-                if (unlikely(error)) {
-                        set_page_private(page, 0UL);
-                        ClearPageSwapCache(page);
-                        page_cache_release(page);
-                }
         }
         return error;
 }
@@ -137,38 +152,34 @@ int add_to_swap(struct page *page)
         VM_BUG_ON(!PageLocked(page));
         VM_BUG_ON(!PageUptodate(page));
 
-        for (;;) {
-                entry = get_swap_page();
-                if (!entry.val)
-                        return 0;
+        entry = get_swap_page();
+        if (!entry.val)
+                return 0;
 
+        /*
+         * Radix-tree node allocations from PF_MEMALLOC contexts could
+         * completely exhaust the page allocator. __GFP_NOMEMALLOC
+         * stops emergency reserves from being allocated.
+         *
+         * TODO: this could cause a theoretical memory reclaim
+         * deadlock in the swap out path.
+         */
+        /*
+         * Add it to the swap cache and mark it dirty
+         */
+        err = add_to_swap_cache(page, entry,
+                        __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
+
+        if (!err) {     /* Success */
+                SetPageDirty(page);
+                return 1;
+        } else {        /* -ENOMEM radix-tree allocation failure */
                 /*
-                 * Radix-tree node allocations from PF_MEMALLOC contexts could
-                 * completely exhaust the page allocator. __GFP_NOMEMALLOC
-                 * stops emergency reserves from being allocated.
-                 *
-                 * TODO: this could cause a theoretical memory reclaim
-                 * deadlock in the swap out path.
-                 */
-                /*
-                 * Add it to the swap cache and mark it dirty
+                 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+                 * clear SWAP_HAS_CACHE flag.
                  */
-                err = add_to_swap_cache(page, entry,
-                                __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
-
-                switch (err) {
-                case 0:                         /* Success */
-                        SetPageDirty(page);
-                        return 1;
-                case -EEXIST:
-                        /* Raced with "speculative" read_swap_cache_async */
-                        swapcache_free(entry, NULL);
-                        continue;
-                default:
-                        /* -ENOMEM radix-tree allocation failure */
-                        swapcache_free(entry, NULL);
-                        return 0;
-                }
+                swapcache_free(entry, NULL);
+                return 0;
         }
 }
 
@@ -290,26 +301,31 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                 }
 
                 /*
+                 * call radix_tree_preload() while we can wait.
+                 */
+                err = radix_tree_preload(gfp_mask & GFP_KERNEL);
+                if (err)
+                        break;
+
+                /*
                  * Swap entry may have been freed since our caller observed it.
                  */
                 err = swapcache_prepare(entry);
-                if (err == -EEXIST) /* seems racy */
+                if (err == -EEXIST) {   /* seems racy */
+                        radix_tree_preload_end();
                         continue;
-                if (err)           /* swp entry is obsolete ? */
+                }
+                if (err) {              /* swp entry is obsolete ? */
+                        radix_tree_preload_end();
                         break;
+                }
 
-                /*
-                 * Associate the page with swap entry in the swap cache.
-                 * May fail (-EEXIST) if there is already a page associated
-                 * with this entry in the swap cache: added by a racing
-                 * read_swap_cache_async, or add_to_swap or shmem_writepage
-                 * re-using the just freed swap entry for an existing page.
-                 * May fail (-ENOMEM) if radix-tree node allocation failed.
-                 */
+                /* May fail (-ENOMEM) if radix-tree node allocation failed. */
                 __set_page_locked(new_page);
                 SetPageSwapBacked(new_page);
-                err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL);
+                err = __add_to_swap_cache(new_page, entry);
                 if (likely(!err)) {
+                        radix_tree_preload_end();
                         /*
                          * Initiate read into locked page and return.
                          */
@@ -317,8 +333,13 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                         swap_readpage(new_page);
                         return new_page;
                 }
+                radix_tree_preload_end();
                 ClearPageSwapBacked(new_page);
                 __clear_page_locked(new_page);
+                /*
+                 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+                 * clear SWAP_HAS_CACHE flag.
+                 */
                 swapcache_free(entry, NULL);
         } while (err != -ENOMEM);