ext4: Add configurable run-time mballoc debugging

Allow mballoc debugging to be enabled at run-time instead of just at
compile time.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/Kconfig

@@ -77,3 +77,12 @@ config EXT4_FS_SECURITY
 
 	  If you are not using a security module that requires using
 	  extended attributes for file security labels, say N.
+
+config EXT4_DEBUG
+	bool "EXT4 debugging support"
+	depends on EXT4_FS
+	help
+	  Enables run-time debugging support for the ext4 filesystem.
+
+	  If you select Y here, then you will be able to turn on debugging
+	  with a command such as "echo 1 > /sys/kernel/debug/ext4/mballoc-debug"

fs/ext4/mballoc.c

@@ -22,6 +22,7 @@
  */
 
 #include "mballoc.h"
+#include <linux/debugfs.h>
 #include <trace/events/ext4.h>
 
 /*
@@ -743,7 +744,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
 	char *data;
 	char *bitmap;
 
-	mb_debug("init page %lu\n", page->index);
+	mb_debug(1, "init page %lu\n", page->index);
 
 	inode = page->mapping->host;
 	sb = inode->i_sb;
@@ -822,7 +823,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
 		set_bitmap_uptodate(bh[i]);
 		bh[i]->b_end_io = end_buffer_read_sync;
 		submit_bh(READ, bh[i]);
-		mb_debug("read bitmap for group %u\n", first_group + i);
+		mb_debug(1, "read bitmap for group %u\n", first_group + i);
 	}
 
 	/* wait for I/O completion */
@@ -862,7 +863,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
 		if ((first_block + i) & 1) {
 			/* this is block of buddy */
 			BUG_ON(incore == NULL);
-			mb_debug("put buddy for group %u in page %lu/%x\n",
+			mb_debug(1, "put buddy for group %u in page %lu/%x\n",
 				group, page->index, i * blocksize);
 			grinfo = ext4_get_group_info(sb, group);
 			grinfo->bb_fragments = 0;
@@ -878,7 +879,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
 		} else {
 			/* this is block of bitmap */
 			BUG_ON(incore != NULL);
-			mb_debug("put bitmap for group %u in page %lu/%x\n",
+			mb_debug(1, "put bitmap for group %u in page %lu/%x\n",
 				group, page->index, i * blocksize);
 
 			/* see comments in ext4_mb_put_pa() */
@@ -922,7 +923,7 @@ ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct inode *inode = sbi->s_buddy_cache;
 
-	mb_debug("load group %u\n", group);
+	mb_debug(1, "load group %u\n", group);
 
 	blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
 	grp = ext4_get_group_info(sb, group);
@@ -1851,7 +1852,7 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
 	struct inode *inode = sbi->s_buddy_cache;
 	struct page *page = NULL, *bitmap_page = NULL;
 
-	mb_debug("init group %u\n", group);
+	mb_debug(1, "init group %u\n", group);
 	blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
 	this_grp = ext4_get_group_info(sb, group);
 	/*
@@ -2739,7 +2740,7 @@ static void ext4_mb_cleanup_pa(struct ext4_group_info *grp)
 		kmem_cache_free(ext4_pspace_cachep, pa);
 	}
 	if (count)
-		mb_debug("mballoc: %u PAs left\n", count);
+		mb_debug(1, "mballoc: %u PAs left\n", count);
 
 }
 
@@ -2820,7 +2821,7 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 	list_for_each_safe(l, ltmp, &txn->t_private_list) {
 		entry = list_entry(l, struct ext4_free_data, list);
 
-		mb_debug("gonna free %u blocks in group %u (0x%p):",
+		mb_debug(1, "gonna free %u blocks in group %u (0x%p):",
 			 entry->count, entry->group, entry);
 
 		err = ext4_mb_load_buddy(sb, entry->group, &e4b);
@@ -2855,9 +2856,43 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 		ext4_mb_release_desc(&e4b);
 	}
 
-	mb_debug("freed %u blocks in %u structures\n", count, count2);
+	mb_debug(1, "freed %u blocks in %u structures\n", count, count2);
 }
 
+#ifdef CONFIG_EXT4_DEBUG
+u8 mb_enable_debug __read_mostly;
+
+static struct dentry *debugfs_dir;
+static struct dentry *debugfs_debug;
+
+static void __init ext4_create_debugfs_entry(void)
+{
+	debugfs_dir = debugfs_create_dir("ext4", NULL);
+	if (debugfs_dir)
+		debugfs_debug = debugfs_create_u8("mballoc-debug",
+						  S_IRUGO | S_IWUSR,
+						  debugfs_dir,
+						  &mb_enable_debug);
+}
+
+static void ext4_remove_debugfs_entry(void)
+{
+	debugfs_remove(debugfs_debug);
+	debugfs_remove(debugfs_dir);
+}
+
+#else
+
+static void __init ext4_create_debugfs_entry(void)
+{
+}
+
+static void ext4_remove_debugfs_entry(void)
+{
+}
+
+#endif
+
 int __init init_ext4_mballoc(void)
 {
 	ext4_pspace_cachep =
@@ -2885,6 +2920,7 @@ int __init init_ext4_mballoc(void)
 		kmem_cache_destroy(ext4_ac_cachep);
 		return -ENOMEM;
 	}
+	ext4_create_debugfs_entry();
 	return 0;
 }
 
@@ -2898,6 +2934,7 @@ void exit_ext4_mballoc(void)
 	kmem_cache_destroy(ext4_pspace_cachep);
 	kmem_cache_destroy(ext4_ac_cachep);
 	kmem_cache_destroy(ext4_free_ext_cachep);
+	ext4_remove_debugfs_entry();
 }
 
 
@@ -3042,7 +3079,7 @@ static void ext4_mb_normalize_group_request(struct ext4_allocation_context *ac)
 		ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_stripe;
 	else
 		ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;
-	mb_debug("#%u: goal %u blocks for locality group\n",
+	mb_debug(1, "#%u: goal %u blocks for locality group\n",
 		current->pid, ac->ac_g_ex.fe_len);
 }
 
@@ -3232,7 +3269,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 		ac->ac_flags |= EXT4_MB_HINT_TRY_GOAL;
 	}
 
-	mb_debug("goal: %u(was %u) blocks at %u\n", (unsigned) size,
+	mb_debug(1, "goal: %u(was %u) blocks at %u\n", (unsigned) size,
 		(unsigned) orig_size, (unsigned) start);
 }
 
@@ -3281,7 +3318,7 @@ static void ext4_mb_use_inode_pa(struct ext4_allocation_context *ac,
 	BUG_ON(pa->pa_free < len);
 	pa->pa_free -= len;
 
-	mb_debug("use %llu/%u from inode pa %p\n", start, len, pa);
+	mb_debug(1, "use %llu/%u from inode pa %p\n", start, len, pa);
 }
 
 /*
@@ -3305,7 +3342,7 @@ static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac,
 	 * in on-disk bitmap -- see ext4_mb_release_context()
 	 * Other CPUs are prevented from allocating from this pa by lg_mutex
 	 */
-	mb_debug("use %u/%u from group pa %p\n", pa->pa_lstart-len, len, pa);
+	mb_debug(1, "use %u/%u from group pa %p\n", pa->pa_lstart-len, len, pa);
 }
 
 /*
@@ -3484,7 +3521,7 @@ void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
 		preallocated += len;
 		count++;
 	}
-	mb_debug("prellocated %u for group %u\n", preallocated, group);
+	mb_debug(1, "prellocated %u for group %u\n", preallocated, group);
 }
 
 static void ext4_mb_pa_callback(struct rcu_head *head)
@@ -3619,7 +3656,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
 	pa->pa_deleted = 0;
 	pa->pa_type = MB_INODE_PA;
 
-	mb_debug("new inode pa %p: %llu/%u for %u\n", pa,
+	mb_debug(1, "new inode pa %p: %llu/%u for %u\n", pa,
 			pa->pa_pstart, pa->pa_len, pa->pa_lstart);
 	trace_ext4_mb_new_inode_pa(ac, pa);
 
@@ -3679,7 +3716,7 @@ ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
 	pa->pa_deleted = 0;
 	pa->pa_type = MB_GROUP_PA;
 
-	mb_debug("new group pa %p: %llu/%u for %u\n", pa,
+	mb_debug(1, "new group pa %p: %llu/%u for %u\n", pa,
 			pa->pa_pstart, pa->pa_len, pa->pa_lstart);
 	trace_ext4_mb_new_group_pa(ac, pa);
 
@@ -3758,7 +3795,7 @@ ext4_mb_release_inode_pa(struct ext4_buddy *e4b, struct buffer_head *bitmap_bh,
 		next = mb_find_next_bit(bitmap_bh->b_data, end, bit);
 		start = group * EXT4_BLOCKS_PER_GROUP(sb) + bit +
 				le32_to_cpu(sbi->s_es->s_first_data_block);
-		mb_debug("    free preallocated %u/%u in group %u\n",
+		mb_debug(1, "    free preallocated %u/%u in group %u\n",
 				(unsigned) start, (unsigned) next - bit,
 				(unsigned) group);
 		free += next - bit;
@@ -3849,7 +3886,7 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
 	int busy = 0;
 	int free = 0;
 
-	mb_debug("discard preallocation for group %u\n", group);
+	mb_debug(1, "discard preallocation for group %u\n", group);
 
 	if (list_empty(&grp->bb_prealloc_list))
 		return 0;
@@ -3973,7 +4010,7 @@ void ext4_discard_preallocations(struct inode *inode)
 		return;
 	}
 
-	mb_debug("discard preallocation for inode %lu\n", inode->i_ino);
+	mb_debug(1, "discard preallocation for inode %lu\n", inode->i_ino);
 	trace_ext4_discard_preallocations(inode);
 
 	INIT_LIST_HEAD(&list);
@@ -4078,7 +4115,7 @@ static void ext4_mb_return_to_preallocation(struct inode *inode,
 {
 	BUG_ON(!list_empty(&EXT4_I(inode)->i_prealloc_list));
 }
-#ifdef MB_DEBUG
+#ifdef CONFIG_EXT4_DEBUG
 static void ext4_mb_show_ac(struct ext4_allocation_context *ac)
 {
 	struct super_block *sb = ac->ac_sb;
@@ -4227,7 +4264,7 @@ ext4_mb_initialize_context(struct ext4_allocation_context *ac,
 	 * locality group. this is a policy, actually */
 	ext4_mb_group_or_file(ac);
 
-	mb_debug("init ac: %u blocks @ %u, goal %u, flags %x, 2^%d, "
+	mb_debug(1, "init ac: %u blocks @ %u, goal %u, flags %x, 2^%d, "
 			"left: %u/%u, right %u/%u to %swritable\n",
 			(unsigned) ar->len, (unsigned) ar->logical,
 			(unsigned) ar->goal, ac->ac_flags, ac->ac_2order,
@@ -4249,7 +4286,7 @@ ext4_mb_discard_lg_preallocations(struct super_block *sb,
 	struct ext4_prealloc_space *pa, *tmp;
 	struct ext4_allocation_context *ac;
 
-	mb_debug("discard locality group preallocation\n");
+	mb_debug(1, "discard locality group preallocation\n");
 
 	INIT_LIST_HEAD(&discard_list);
 	ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);

fs/ext4/mballoc.h

@@ -37,11 +37,19 @@
 
 /*
  */
-#define MB_DEBUG__
-#ifdef MB_DEBUG
-#define mb_debug(fmt, a...)	printk(fmt, ##a)
+#ifdef CONFIG_EXT4_DEBUG
+extern u8 mb_enable_debug;
+
+#define mb_debug(n, fmt, a...)	                                        \
+	do {								\
+		if ((n) <= mb_enable_debug) {		        	\
+			printk(KERN_DEBUG "(%s, %d): %s: ",		\
+			       __FILE__, __LINE__, __func__);		\
+			printk(fmt, ## a);				\
+		}							\
+	} while (0)
 #else
-#define mb_debug(fmt, a...)
+#define mb_debug(n, fmt, a...)
 #endif
 
 /*