writeback: restructure try_writeback_inodes_sb[_nr]()

try_writeback_inodes_sb_nr() wraps writeback_inodes_sb_nr() so that it
handles s_umount locking and skips if writeback is already in
progress.  The in progress test is performed on the root wb
(bdi_writeback) which isn't sufficient for cgroup writeback support.
The test must be done per-wb.

To prepare for the change, this patch factors out
__writeback_inodes_sb_nr() from writeback_inodes_sb_nr() and adds
@skip_if_busy and moves the in progress test right before queueing the
wb_writeback_work.  try_writeback_inodes_sb_nr() now just grabs
s_umount and invokes __writeback_inodes_sb_nr() with asserted
@skip_if_busy.  This way, later addition of multiple wb handling can
skip only the wb's which already have writeback in progress.

This swaps the order between in progress test and s_umount test which
can flip the return value when writeback is in progress and s_umount
is being held by someone else but this shouldn't cause any meaningful
difference.  It's a fringe condition and the return value is an
unsynchronized hint anyway.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 093b9594e846008b4010420c9a25c96d24e1143d..0039c5839cdd6e66444ea1cbc135858735cf4c4c 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1581,19 +1581,8 @@ static void wait_sb_inodes(struct super_block *sb)
        iput(old_inode);
 }
 
-/**
- * writeback_inodes_sb_nr -    writeback dirty inodes from given super_block
- * @sb: the superblock
- * @nr: the number of pages to write
- * @reason: reason why some writeback work initiated
- *
- * 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.
- */
-void writeback_inodes_sb_nr(struct super_block *sb,
-                           unsigned long nr,
-                           enum wb_reason reason)
+static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
+                                    enum wb_reason reason, bool skip_if_busy)
 {
        DEFINE_WB_COMPLETION_ONSTACK(done);
        struct wb_writeback_work work = {
@@ -1609,9 +1598,30 @@ void writeback_inodes_sb_nr(struct super_block *sb,
        if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
                return;
        WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+       if (skip_if_busy && writeback_in_progress(&bdi->wb))
+               return;
+
        wb_queue_work(&bdi->wb, &work);
        wb_wait_for_completion(bdi, &done);
 }
+
+/**
+ * writeback_inodes_sb_nr -    writeback dirty inodes from given super_block
+ * @sb: the superblock
+ * @nr: the number of pages to write
+ * @reason: reason why some writeback work initiated
+ *
+ * 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.
+ */
+void writeback_inodes_sb_nr(struct super_block *sb,
+                           unsigned long nr,
+                           enum wb_reason reason)
+{
+       __writeback_inodes_sb_nr(sb, nr, reason, false);
+}
 EXPORT_SYMBOL(writeback_inodes_sb_nr);
 
 /**
@@ -1638,19 +1648,15 @@ EXPORT_SYMBOL(writeback_inodes_sb);
  * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
  */
-int try_to_writeback_inodes_sb_nr(struct super_block *sb,
-                                 unsigned long nr,
-                                 enum wb_reason reason)
+bool try_to_writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
+                                  enum wb_reason reason)
 {
-       if (writeback_in_progress(&sb->s_bdi->wb))
-               return 1;
-
        if (!down_read_trylock(&sb->s_umount))
-               return 0;
+               return false;
 
-       writeback_inodes_sb_nr(sb, nr, reason);
+       __writeback_inodes_sb_nr(sb, nr, reason, true);
        up_read(&sb->s_umount);
-       return 1;
+       return true;
 }
 EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
 
@@ -1662,7 +1668,7 @@ EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
  * 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)
+bool 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);
 }

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index a6b9db7fcee8c43ab97d036d65d04962f632de79..23af355d547154072d52e56c70aebe2836ea9598 100644 (file)
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -93,9 +93,9 @@ struct bdi_writeback;
 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 try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
-int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
-                                 enum wb_reason reason);
+bool try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
+bool try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
+                                  enum wb_reason reason);
 void sync_inodes_sb(struct super_block *);
 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason);
 void inode_wait_for_writeback(struct inode *inode);