1 files changed, 28 insertions, 5 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index efc6387..05c44aa 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -107,12 +107,33 @@
  *   ->tasklist_lock            (memory_failure, collect_procs_ao)
  */
 
+static void page_cache_tree_delete(struct address_space *mapping,
+				   struct page *page, void *shadow)
+{
+	if (shadow) {
+		void **slot;
+
+		slot = radix_tree_lookup_slot(&mapping->page_tree, page->index);
+		radix_tree_replace_slot(slot, shadow);
+		mapping->nrshadows++;
+		/*
+		 * Make sure the nrshadows update is committed before
+		 * the nrpages update so that final truncate racing
+		 * with reclaim does not see both counters 0 at the
+		 * same time and miss a shadow entry.
+		 */
+		smp_wmb();
+	} else
+		radix_tree_delete(&mapping->page_tree, page->index);
+	mapping->nrpages--;
+}
+
 /*
  * Delete a page from the page cache and free it. Caller has to make
  * sure the page is locked and that nobody else uses it - or that usage
  * is safe.  The caller must hold the mapping's tree_lock.
  */
-void __delete_from_page_cache(struct page *page)
+void __delete_from_page_cache(struct page *page, void *shadow)
 {
 	struct address_space *mapping = page->mapping;
 
@@ -127,10 +148,11 @@ void __delete_from_page_cache(struct page *page)
 	else
 		cleancache_invalidate_page(mapping, page);
 
-	radix_tree_delete(&mapping->page_tree, page->index);
+	page_cache_tree_delete(mapping, page, shadow);
+
 	page->mapping = NULL;
 	/* Leave page->index set: truncation lookup relies upon it */
-	mapping->nrpages--;
+
 	__dec_zone_page_state(page, NR_FILE_PAGES);
 	if (PageSwapBacked(page))
 		__dec_zone_page_state(page, NR_SHMEM);
@@ -166,7 +188,7 @@ void delete_from_page_cache(struct page *page)
 
 	freepage = mapping->a_ops->freepage;
 	spin_lock_irq(&mapping->tree_lock);
-	__delete_from_page_cache(page);
+	__delete_from_page_cache(page, NULL);
 	spin_unlock_irq(&mapping->tree_lock);
 	mem_cgroup_uncharge_cache_page(page);
 
@@ -426,7 +448,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
 		new->index = offset;
 
 		spin_lock_irq(&mapping->tree_lock);
-		__delete_from_page_cache(old);
+		__delete_from_page_cache(old, NULL);
 		error = radix_tree_insert(&mapping->page_tree, offset, new);
 		BUG_ON(error);
 		mapping->nrpages++;
@@ -460,6 +482,7 @@ static int page_cache_tree_insert(struct address_space *mapping,
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
 		radix_tree_replace_slot(slot, page);
+		mapping->nrshadows--;
 		mapping->nrpages++;
 		return 0;
 	}