fault-injection: add min-order parameter to fail_page_alloc

Limiting smaller allocation failures by fault injection helps to find real
possible bugs.  Because higher order allocations are likely to fail and
zero-order allocations are not likely to fail.

This patch adds min-order parameter to fail_page_alloc.  It specifies the
minimum page allocation order to be injected failures.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/fault-injection/fault-injection.txt

@@ -103,6 +103,11 @@ configuration of fault-injection capabilities.
 	default is 'N', setting it to 'Y' will inject failures
 	only into non-sleep allocations (GFP_ATOMIC allocations).
 
+- /debug/fail_page_alloc/min-order:
+
+	specifies the minimum page allocation order to be injected
+	failures.
+
 o Boot option
 
 In order to inject faults while debugfs is not available (early boot time),

mm/page_alloc.c

@@ -900,18 +900,21 @@ static struct fail_page_alloc_attr {
 
 	u32 ignore_gfp_highmem;
 	u32 ignore_gfp_wait;
+	u32 min_order;
 
 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
 
 	struct dentry *ignore_gfp_highmem_file;
 	struct dentry *ignore_gfp_wait_file;
+	struct dentry *min_order_file;
 
 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
 
 } fail_page_alloc = {
 	.attr = FAULT_ATTR_INITIALIZER,
 	.ignore_gfp_wait = 1,
 	.ignore_gfp_highmem = 1,
+	.min_order = 1,
 };
 
 static int __init setup_fail_page_alloc(char *str)
@@ -922,6 +925,8 @@ __setup("fail_page_alloc=", setup_fail_page_alloc);
 
 static int should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
 {
+	if (order < fail_page_alloc.min_order)
+		return 0;
 	if (gfp_mask & __GFP_NOFAIL)
 		return 0;
 	if (fail_page_alloc.ignore_gfp_highmem && (gfp_mask & __GFP_HIGHMEM))
@@ -953,12 +958,17 @@ static int __init fail_page_alloc_debugfs(void)
 	fail_page_alloc.ignore_gfp_highmem_file =
 		debugfs_create_bool("ignore-gfp-highmem", mode, dir,
 				      &fail_page_alloc.ignore_gfp_highmem);
+	fail_page_alloc.min_order_file =
+		debugfs_create_u32("min-order", mode, dir,
+				   &fail_page_alloc.min_order);
 
 	if (!fail_page_alloc.ignore_gfp_wait_file ||
-			!fail_page_alloc.ignore_gfp_highmem_file) {
+            !fail_page_alloc.ignore_gfp_highmem_file ||
+            !fail_page_alloc.min_order_file) {
 		err = -ENOMEM;
 		debugfs_remove(fail_page_alloc.ignore_gfp_wait_file);
 		debugfs_remove(fail_page_alloc.ignore_gfp_highmem_file);
+		debugfs_remove(fail_page_alloc.min_order_file);
 		cleanup_fault_attr_dentries(&fail_page_alloc.attr);
 	}