writeback: get rid of generic_sync_sb_inodes() export

This adds two new exported functions:

- writeback_inodes_sb(), which only attempts to writeback dirty inodes on
  this super_block, for WB_SYNC_NONE writeout.
- sync_inodes_sb(), which writes out all dirty inodes on this super_block
  and also waits for the IO to complete.

Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/staging/pohmelfs/inode.c

@@ -1950,14 +1950,7 @@ static int pohmelfs_get_sb(struct file_system_type *fs_type,
  */
 static void pohmelfs_kill_super(struct super_block *sb)
 {
-	struct writeback_control wbc = {
-		.sync_mode	= WB_SYNC_ALL,
-		.range_start	= 0,
-		.range_end	= LLONG_MAX,
-		.nr_to_write	= LONG_MAX,
-	};
-	generic_sync_sb_inodes(sb, &wbc);
-
+	sync_inodes_sb(sb);
 	kill_anon_super(sb);
 }
 

fs/fs-writeback.c

@@ -458,8 +458,8 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
  * on the writer throttling path, and we get decent balancing between many
  * throttled threads: we don't want them all piling up on inode_sync_wait.
  */
-void generic_sync_sb_inodes(struct super_block *sb,
-				struct writeback_control *wbc)
+static void generic_sync_sb_inodes(struct super_block *sb,
+				   struct writeback_control *wbc)
 {
 	const unsigned long start = jiffies;	/* livelock avoidance */
 	int sync = wbc->sync_mode == WB_SYNC_ALL;
@@ -593,13 +593,6 @@ void generic_sync_sb_inodes(struct super_block *sb,
 
 	return;		/* Leave any unwritten inodes on s_io */
 }
-EXPORT_SYMBOL_GPL(generic_sync_sb_inodes);
-
-static void sync_sb_inodes(struct super_block *sb,
-				struct writeback_control *wbc)
-{
-	generic_sync_sb_inodes(sb, wbc);
-}
 
 /*
  * Start writeback of dirty pagecache data against all unlocked inodes.
@@ -640,7 +633,7 @@ restart:
 			 */
 			if (down_read_trylock(&sb->s_umount)) {
 				if (sb->s_root)
-					sync_sb_inodes(sb, wbc);
+					generic_sync_sb_inodes(sb, wbc);
 				up_read(&sb->s_umount);
 			}
 			spin_lock(&sb_lock);
@@ -653,35 +646,56 @@ restart:
 	spin_unlock(&sb_lock);
 }
 
-/*
- * writeback and wait upon the filesystem's dirty inodes.  The caller will
- * do this in two passes - one to write, and one to wait.
+/**
+ * writeback_inodes_sb	-	writeback dirty inodes from given super_block
+ * @sb: the superblock
  *
- * A finite limit is set on the number of pages which will be written.
- * To prevent infinite livelock of sys_sync().
- *
- * We add in the number of potentially dirty inodes, because each inode write
- * can dirty pagecache in the underlying blockdev.
+ * Start writeback on some inodes on this super_block. No guarantees are made
+ * on how many (if any) will be written, and this function does not wait
+ * for IO completion of submitted IO. The number of pages submitted is
+ * returned.
  */
-void sync_inodes_sb(struct super_block *sb, int wait)
+long writeback_inodes_sb(struct super_block *sb)
 {
 	struct writeback_control wbc = {
-		.sync_mode	= wait ? WB_SYNC_ALL : WB_SYNC_NONE,
+		.sync_mode	= WB_SYNC_NONE,
 		.range_start	= 0,
 		.range_end	= LLONG_MAX,
 	};
+	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
+	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
+	long nr_to_write;
 
-	if (!wait) {
-		unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
-		unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
-
-		wbc.nr_to_write = nr_dirty + nr_unstable +
+	nr_to_write = nr_dirty + nr_unstable +
 			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
-	} else
-		wbc.nr_to_write = LONG_MAX; /* doesn't actually matter */
 
-	sync_sb_inodes(sb, &wbc);
+	wbc.nr_to_write = nr_to_write;
+	generic_sync_sb_inodes(sb, &wbc);
+	return nr_to_write - wbc.nr_to_write;
 }
+EXPORT_SYMBOL(writeback_inodes_sb);
+
+/**
+ * sync_inodes_sb	-	sync sb inode pages
+ * @sb: the superblock
+ *
+ * This function writes and waits on any dirty inode belonging to this
+ * super_block. The number of pages synced is returned.
+ */
+long sync_inodes_sb(struct super_block *sb)
+{
+	struct writeback_control wbc = {
+		.sync_mode	= WB_SYNC_ALL,
+		.range_start	= 0,
+		.range_end	= LLONG_MAX,
+	};
+	long nr_to_write = LONG_MAX; /* doesn't actually matter */
+
+	wbc.nr_to_write = nr_to_write;
+	generic_sync_sb_inodes(sb, &wbc);
+	return nr_to_write - wbc.nr_to_write;
+}
+EXPORT_SYMBOL(sync_inodes_sb);
 
 /**
  * write_inode_now	-	write an inode to disk

fs/sync.c

@@ -19,20 +19,22 @@
 			SYNC_FILE_RANGE_WAIT_AFTER)
 
 /*
- * Do the filesystem syncing work. For simple filesystems sync_inodes_sb(sb, 0)
- * just dirties buffers with inodes so we have to submit IO for these buffers
- * via __sync_blockdev(). This also speeds up the wait == 1 case since in that
- * case write_inode() functions do sync_dirty_buffer() and thus effectively
- * write one block at a time.
+ * Do the filesystem syncing work. For simple filesystems
+ * writeback_inodes_sb(sb) just dirties buffers with inodes so we have to
+ * submit IO for these buffers via __sync_blockdev(). This also speeds up the
+ * wait == 1 case since in that case write_inode() functions do
+ * sync_dirty_buffer() and thus effectively write one block at a time.
  */
 static int __sync_filesystem(struct super_block *sb, int wait)
 {
 	/* Avoid doing twice syncing and cache pruning for quota sync */
-	if (!wait)
+	if (!wait) {
 		writeout_quota_sb(sb, -1);
-	else
+		writeback_inodes_sb(sb);
+	} else {
 		sync_quota_sb(sb, -1);
-	sync_inodes_sb(sb, wait);
+		sync_inodes_sb(sb);
+	}
 	if (sb->s_op->sync_fs)
 		sb->s_op->sync_fs(sb, wait);
 	return __sync_blockdev(sb->s_bdev, wait);

fs/ubifs/budget.c

@@ -65,26 +65,14 @@
 static int shrink_liability(struct ubifs_info *c, int nr_to_write)
 {
 	int nr_written;
-	struct writeback_control wbc = {
-		.sync_mode   = WB_SYNC_NONE,
-		.range_end   = LLONG_MAX,
-		.nr_to_write = nr_to_write,
-	};
-
-	generic_sync_sb_inodes(c->vfs_sb, &wbc);
-	nr_written = nr_to_write - wbc.nr_to_write;
 
+	nr_written = writeback_inodes_sb(c->vfs_sb);
 	if (!nr_written) {
 		/*
 		 * Re-try again but wait on pages/inodes which are being
 		 * written-back concurrently (e.g., by pdflush).
 		 */
-		memset(&wbc, 0, sizeof(struct writeback_control));
-		wbc.sync_mode   = WB_SYNC_ALL;
-		wbc.range_end   = LLONG_MAX;
-		wbc.nr_to_write = nr_to_write;
-		generic_sync_sb_inodes(c->vfs_sb, &wbc);
-		nr_written = nr_to_write - wbc.nr_to_write;
+		nr_written = sync_inodes_sb(c->vfs_sb);
 	}
 
 	dbg_budg("%d pages were written back", nr_written);

fs/ubifs/super.c

@@ -438,12 +438,6 @@ static int ubifs_sync_fs(struct super_block *sb, int wait)
 {
 	int i, err;
 	struct ubifs_info *c = sb->s_fs_info;
-	struct writeback_control wbc = {
-		.sync_mode   = WB_SYNC_ALL,
-		.range_start = 0,
-		.range_end   = LLONG_MAX,
-		.nr_to_write = LONG_MAX,
-	};
 
 	/*
 	 * Zero @wait is just an advisory thing to help the file system shove
@@ -462,7 +456,7 @@ static int ubifs_sync_fs(struct super_block *sb, int wait)
 	 * the user be able to get more accurate results of 'statfs()' after
 	 * they synchronize the file system.
 	 */
-	generic_sync_sb_inodes(sb, &wbc);
+	sync_inodes_sb(sb);
 
 	/*
 	 * Synchronize write buffers, because 'ubifs_run_commit()' does not

include/linux/fs.h

@@ -2071,8 +2071,6 @@ static inline void invalidate_remote_inode(struct inode *inode)
 extern int invalidate_inode_pages2(struct address_space *mapping);
 extern int invalidate_inode_pages2_range(struct address_space *mapping,
 					 pgoff_t start, pgoff_t end);
-extern void generic_sync_sb_inodes(struct super_block *sb,
-				struct writeback_control *wbc);
 extern int write_inode_now(struct inode *, int);
 extern int filemap_fdatawrite(struct address_space *);
 extern int filemap_flush(struct address_space *);

include/linux/writeback.h

@@ -78,7 +78,8 @@ struct writeback_control {
  */	
 void writeback_inodes(struct writeback_control *wbc);
 int inode_wait(void *);
-void sync_inodes_sb(struct super_block *, int wait);
+long writeback_inodes_sb(struct super_block *);
+long sync_inodes_sb(struct super_block *);
 
 /* writeback.h requires fs.h; it, too, is not included from here. */
 static inline void wait_on_inode(struct inode *inode)