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 093b959..0039c58 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1581,19 +1581,8 @@
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 @@
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 @@
* 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 @@
* 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);
}