ext4: Clean up s_dirt handling

We don't need to set s_dirt in most of the ext4 code when journaling
is enabled.  In ext3/4 some of the summary statistics for # of free
inodes, blocks, and directories are calculated from the per-block
group statistics when the file system is mounted or unmounted.  As a
result the superblock doesn't have to be updated, either via the
journal or by setting s_dirt.  There are a few exceptions, most
notably when resizing the file system, where the superblock needs to
be modified --- and in that case it should be done as a journalled
operation if possible, and s_dirt set only in no-journal mode.

This patch will optimize out some unneeded disk writes when using ext4
with a journal.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/balloc.c

@@ -377,14 +377,11 @@ void ext4_add_groupblocks(handle_t *handle, struct super_block *sb,
 	ext4_grpblk_t bit;
 	unsigned int i;
 	struct ext4_group_desc *desc;
-	struct ext4_super_block *es;
-	struct ext4_sb_info *sbi;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	int err = 0, ret, blk_free_count;
 	ext4_grpblk_t blocks_freed;
 	struct ext4_group_info *grp;
 
-	sbi = EXT4_SB(sb);
-	es = sbi->s_es;
 	ext4_debug("Adding block(s) %llu-%llu\n", block, block + count - 1);
 
 	ext4_get_group_no_and_offset(sb, block, &block_group, &bit);
@@ -477,7 +474,6 @@ void ext4_add_groupblocks(handle_t *handle, struct super_block *sb,
 	ret = ext4_handle_dirty_metadata(handle, NULL, gd_bh);
 	if (!err)
 		err = ret;
-	sb->s_dirt = 1;
 
 error_return:
 	brelse(bitmap_bh);

fs/ext4/ext4.h

@@ -1860,6 +1860,12 @@ static inline void ext4_unlock_group(struct super_block *sb,
 	spin_unlock(ext4_group_lock_ptr(sb, group));
 }
 
+static inline void ext4_mark_super_dirty(struct super_block *sb)
+{
+	if (EXT4_SB(sb)->s_journal == NULL)
+		sb->s_dirt =1;
+}
+
 /*
  * Inodes and files operations
  */

fs/ext4/ext4_jbd2.c

@@ -143,3 +143,19 @@ int __ext4_handle_dirty_metadata(const char *where, handle_t *handle,
 	}
 	return err;
 }
+
+int __ext4_handle_dirty_super(const char *where, handle_t *handle,
+			      struct super_block *sb)
+{
+	struct buffer_head *bh = EXT4_SB(sb)->s_sbh;
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_dirty_metadata(handle, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	} else
+		sb->s_dirt = 1;
+	return err;
+}

fs/ext4/ext4_jbd2.h

@@ -141,6 +141,9 @@ int __ext4_journal_get_create_access(const char *where,
 int __ext4_handle_dirty_metadata(const char *where, handle_t *handle,
 				 struct inode *inode, struct buffer_head *bh);
 
+int __ext4_handle_dirty_super(const char *where, handle_t *handle,
+			      struct super_block *sb);
+
 #define ext4_journal_get_undo_access(handle, bh) \
 	__ext4_journal_get_undo_access(__func__, (handle), (bh))
 #define ext4_journal_get_write_access(handle, bh) \
@@ -152,6 +155,8 @@ int __ext4_handle_dirty_metadata(const char *where, handle_t *handle,
 	__ext4_journal_get_create_access(__func__, (handle), (bh))
 #define ext4_handle_dirty_metadata(handle, inode, bh) \
 	__ext4_handle_dirty_metadata(__func__, (handle), (inode), (bh))
+#define ext4_handle_dirty_super(handle, sb) \
+	__ext4_handle_dirty_super(__func__, (handle), (sb))
 
 handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks);
 int __ext4_journal_stop(const char *where, handle_t *handle);

fs/ext4/file.c

@@ -123,7 +123,7 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 		if (!IS_ERR(cp)) {
 			memcpy(sbi->s_es->s_last_mounted, cp,
 			       sizeof(sbi->s_es->s_last_mounted));
-			sb->s_dirt = 1;
+			ext4_mark_super_dirty(sb);
 		}
 	}
 	return dquot_file_open(inode, filp);

fs/ext4/ialloc.c

@@ -279,7 +279,7 @@ void ext4_free_inode(handle_t *handle, struct inode *inode)
 		err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
 		if (!fatal)
 			fatal = err;
-		sb->s_dirt = 1;
+		ext4_mark_super_dirty(sb);
 	} else
 		ext4_error(sb, "bit already cleared for inode %lu", ino);
 
@@ -965,7 +965,7 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode,
 	percpu_counter_dec(&sbi->s_freeinodes_counter);
 	if (S_ISDIR(mode))
 		percpu_counter_inc(&sbi->s_dirs_counter);
-	sb->s_dirt = 1;
+	ext4_mark_super_dirty(sb);
 
 	if (sbi->s_log_groups_per_flex) {
 		flex_group = ext4_flex_group(sbi, group);

fs/ext4/mballoc.c

@@ -2812,7 +2812,7 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
 	err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
 
 out_err:
-	sb->s_dirt = 1;
+	ext4_mark_super_dirty(sb);
 	brelse(bitmap_bh);
 	return err;
 }
@@ -4680,7 +4680,7 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 		put_bh(bitmap_bh);
 		goto do_more;
 	}
-	sb->s_dirt = 1;
+	ext4_mark_super_dirty(sb);
 error_return:
 	if (freed)
 		dquot_free_block(inode, freed);

fs/ext4/resize.c

@@ -921,8 +921,7 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
 			   &sbi->s_flex_groups[flex_group].free_inodes);
 	}
 
-	ext4_handle_dirty_metadata(handle, NULL, sbi->s_sbh);
-	sb->s_dirt = 1;
+	ext4_handle_dirty_super(handle, sb);
 
 exit_journal:
 	mutex_unlock(&sbi->s_resize_lock);
@@ -1045,13 +1044,12 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es,
 		goto exit_put;
 	}
 	ext4_blocks_count_set(es, o_blocks_count + add);
-	ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
-	sb->s_dirt = 1;
 	mutex_unlock(&EXT4_SB(sb)->s_resize_lock);
 	ext4_debug("freeing blocks %llu through %llu\n", o_blocks_count,
 		   o_blocks_count + add);
 	/* We add the blocks to the bitmap and set the group need init bit */
 	ext4_add_groupblocks(handle, sb, o_blocks_count, add);
+	ext4_handle_dirty_super(handle, sb);
 	ext4_debug("freed blocks %llu through %llu\n", o_blocks_count,
 		   o_blocks_count + add);
 	if ((err = ext4_journal_stop(handle)))

fs/ext4/xattr.c

@@ -458,8 +458,7 @@ static void ext4_xattr_update_super_block(handle_t *handle,
 
 	if (ext4_journal_get_write_access(handle, EXT4_SB(sb)->s_sbh) == 0) {
 		EXT4_SET_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_EXT_ATTR);
-		sb->s_dirt = 1;
-		ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
+		ext4_handle_dirty_super(handle, sb);
 	}
 }