1 files changed, 49 insertions, 21 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 0618fda..566f9a4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1222,6 +1222,7 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
 	struct shmem_sb_info *sbinfo;
 	struct page *filepage = *pagep;
 	struct page *swappage;
+	struct page *prealloc_page = NULL;
 	swp_entry_t *entry;
 	swp_entry_t swap;
 	gfp_t gfp;
@@ -1246,7 +1247,6 @@ repeat:
 		filepage = find_lock_page(mapping, idx);
 	if (filepage && PageUptodate(filepage))
 		goto done;
-	error = 0;
 	gfp = mapping_gfp_mask(mapping);
 	if (!filepage) {
 		/*
@@ -1257,7 +1257,19 @@ repeat:
 		if (error)
 			goto failed;
 		radix_tree_preload_end();
+		if (sgp != SGP_READ && !prealloc_page) {
+			/* We don't care if this fails */
+			prealloc_page = shmem_alloc_page(gfp, info, idx);
+			if (prealloc_page) {
+				if (mem_cgroup_cache_charge(prealloc_page,
+						current->mm, GFP_KERNEL)) {
+					page_cache_release(prealloc_page);
+					prealloc_page = NULL;
+				}
+			}
+		}
 	}
+	error = 0;
 
 	spin_lock(&info->lock);
 	shmem_recalc_inode(inode);
@@ -1405,28 +1417,38 @@ repeat:
 		if (!filepage) {
 			int ret;
 
-			spin_unlock(&info->lock);
-			filepage = shmem_alloc_page(gfp, info, idx);
-			if (!filepage) {
-				shmem_unacct_blocks(info->flags, 1);
-				shmem_free_blocks(inode, 1);
-				error = -ENOMEM;
-				goto failed;
-			}
-			SetPageSwapBacked(filepage);
+			if (!prealloc_page) {
+				spin_unlock(&info->lock);
+				filepage = shmem_alloc_page(gfp, info, idx);
+				if (!filepage) {
+					shmem_unacct_blocks(info->flags, 1);
+					shmem_free_blocks(inode, 1);
+					error = -ENOMEM;
+					goto failed;
+				}
+				SetPageSwapBacked(filepage);
 
-			/* Precharge page while we can wait, compensate after */
-			error = mem_cgroup_cache_charge(filepage, current->mm,
-					GFP_KERNEL);
-			if (error) {
-				page_cache_release(filepage);
-				shmem_unacct_blocks(info->flags, 1);
-				shmem_free_blocks(inode, 1);
-				filepage = NULL;
-				goto failed;
+				/*
+				 * Precharge page while we can wait, compensate
+				 * after
+				 */
+				error = mem_cgroup_cache_charge(filepage,
+					current->mm, GFP_KERNEL);
+				if (error) {
+					page_cache_release(filepage);
+					shmem_unacct_blocks(info->flags, 1);
+					shmem_free_blocks(inode, 1);
+					filepage = NULL;
+					goto failed;
+				}
+
+				spin_lock(&info->lock);
+			} else {
+				filepage = prealloc_page;
+				prealloc_page = NULL;
+				SetPageSwapBacked(filepage);
 			}
 
-			spin_lock(&info->lock);
 			entry = shmem_swp_alloc(info, idx, sgp);
 			if (IS_ERR(entry))
 				error = PTR_ERR(entry);
@@ -1467,13 +1489,19 @@ repeat:
 	}
 done:
 	*pagep = filepage;
-	return 0;
+	error = 0;
+	goto out;
 
 failed:
 	if (*pagep != filepage) {
 		unlock_page(filepage);
 		page_cache_release(filepage);
 	}
+out:
+	if (prealloc_page) {
+		mem_cgroup_uncharge_cache_page(prealloc_page);
+		page_cache_release(prealloc_page);
+	}
 	return error;
 }