2 writeback fixes

- fix negative (setpoint - dirty) in 32bit archs
 - use down_read_trylock() in writeback_inodes_sb(_nr)_if_idle()
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Merge tag 'writeback-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux

Pull writeback fixes from Wu Fengguang:
 "Two writeback fixes

   - fix negative (setpoint - dirty) in 32bit archs

   - use down_read_trylock() in writeback_inodes_sb(_nr)_if_idle()"

* tag 'writeback-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux:
  Negative (setpoint-dirty) in bdi_position_ratio()
  vfs: re-implement writeback_inodes_sb(_nr)_if_idle() and rename them

fs/btrfs/extent-tree.c

@@ -3689,20 +3689,6 @@ static int can_overcommit(struct btrfs_root *root,
 	return 0;
 }
 
-static int writeback_inodes_sb_nr_if_idle_safe(struct super_block *sb,
-					       unsigned long nr_pages,
-					       enum wb_reason reason)
-{
-	if (!writeback_in_progress(sb->s_bdi) &&
-	    down_read_trylock(&sb->s_umount)) {
-		writeback_inodes_sb_nr(sb, nr_pages, reason);
-		up_read(&sb->s_umount);
-		return 1;
-	}
-
-	return 0;
-}
-
 /*
  * shrink metadata reservation for delalloc
  */
@@ -3735,9 +3721,9 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
 	while (delalloc_bytes && loops < 3) {
 		max_reclaim = min(delalloc_bytes, to_reclaim);
 		nr_pages = max_reclaim >> PAGE_CACHE_SHIFT;
-		writeback_inodes_sb_nr_if_idle_safe(root->fs_info->sb,
+		try_to_writeback_inodes_sb_nr(root->fs_info->sb,
-						    nr_pages,
+					      nr_pages,
-						    WB_REASON_FS_FREE_SPACE);
+					      WB_REASON_FS_FREE_SPACE);
 
 		/*
 		 * We need to wait for the async pages to actually start before

fs/ext4/inode.c

@@ -2512,12 +2512,8 @@ static int ext4_nonda_switch(struct super_block *sb)
 	/*
 	 * Start pushing delalloc when 1/2 of free blocks are dirty.
 	 */
-	if (dirty_blocks && (free_blocks < 2 * dirty_blocks) &&
+	if (dirty_blocks && (free_blocks < 2 * dirty_blocks))
-	    !writeback_in_progress(sb->s_bdi) &&
+		try_to_writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
-	    down_read_trylock(&sb->s_umount)) {
-		writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
-		up_read(&sb->s_umount);
-	}
 
 	if (2 * free_blocks < 3 * dirty_blocks ||
 		free_blocks < (dirty_blocks + EXT4_FREECLUSTERS_WATERMARK)) {

fs/fs-writeback.c

@@ -1344,47 +1344,43 @@ void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
 EXPORT_SYMBOL(writeback_inodes_sb);
 
 /**
- * writeback_inodes_sb_if_idle	-	start writeback if none underway
+ * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
- * @sb: the superblock
- * @reason: reason why some writeback work was initiated
- *
- * Invoke writeback_inodes_sb if no writeback is currently underway.
- * Returns 1 if writeback was started, 0 if not.
- */
-int writeback_inodes_sb_if_idle(struct super_block *sb, enum wb_reason reason)
-{
-	if (!writeback_in_progress(sb->s_bdi)) {
-		down_read(&sb->s_umount);
-		writeback_inodes_sb(sb, reason);
-		up_read(&sb->s_umount);
-		return 1;
-	} else
-		return 0;
-}
-EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
-
-/**
- * writeback_inodes_sb_nr_if_idle	-	start writeback if none underway
  * @sb: the superblock
  * @nr: the number of pages to write
- * @reason: reason why some writeback work was initiated
+ * @reason: the reason of writeback
  *
- * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
  */
-int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
+int try_to_writeback_inodes_sb_nr(struct super_block *sb,
-				   unsigned long nr,
+				  unsigned long nr,
-				   enum wb_reason reason)
+				  enum wb_reason reason)
 {
-	if (!writeback_in_progress(sb->s_bdi)) {
+	if (writeback_in_progress(sb->s_bdi))
-		down_read(&sb->s_umount);
-		writeback_inodes_sb_nr(sb, nr, reason);
-		up_read(&sb->s_umount);
 		return 1;
-	} else
+
+	if (!down_read_trylock(&sb->s_umount))
 		return 0;
+
+	writeback_inodes_sb_nr(sb, nr, reason);
+	up_read(&sb->s_umount);
+	return 1;
 }
-EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
+EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
+
+/**
+ * try_to_writeback_inodes_sb - try to start writeback if none underway
+ * @sb: the superblock
+ * @reason: reason why some writeback work was initiated
+ *
+ * Implement by try_to_writeback_inodes_sb_nr()
+ * Returns 1 if writeback was started, 0 if not.
+ */
+int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
+{
+	return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
+}
+EXPORT_SYMBOL(try_to_writeback_inodes_sb);
 
 /**
  * sync_inodes_sb	-	sync sb inode pages

include/linux/writeback.h

@@ -87,9 +87,9 @@ int inode_wait(void *);
 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
 							enum wb_reason reason);
-int writeback_inodes_sb_if_idle(struct super_block *, enum wb_reason reason);
+int try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
-int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr,
+int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
-							enum wb_reason reason);
+				  enum wb_reason reason);
 void sync_inodes_sb(struct super_block *);
 long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
 				enum wb_reason reason);

mm/page-writeback.c

@@ -696,7 +696,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
 	 *     => fast response on large errors; small oscillation near setpoint
 	 */
 	setpoint = (freerun + limit) / 2;
-	x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
+	x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
 		    limit - setpoint + 1);
 	pos_ratio = x;
 	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;