linux-kernel - [179/197] fs-writeback: Add helper function to start writeback if idle

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Date:	Thu, 22 Apr 2010 12:10:30 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Eric Sandeen <sandeen@...hat.com>, Jan Kara <jack@...e.cz>,
	maximilian attems <max@...o.at>
Subject: [179/197] fs-writeback: Add helper function to start writeback if idle

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Eric Sandeen <sandeen@...hat.com>

commit 17bd55d037a02b04d9119511cfd1a4b985d20f63 upstream.

ext4, at least, would like to start pushing on writeback if it starts
to get close to ENOSPC when reserving worst-case blocks for delalloc
writes.  Writing out delalloc data will convert those worst-case
predictions into usually smaller actual usage, freeing up space
before we hit ENOSPC based on this speculation.

Thanks to Jens for the suggestion for the helper function,
& the naming help.

I've made the helper return status on whether writeback was
started even though I don't plan to use it in the ext4 patch;
it seems like it would be potentially useful to test this
in some cases.

Signed-off-by: Eric Sandeen <sandeen@...hat.com>
Acked-by: Jan Kara <jack@...e.cz>
Cc: maximilian attems <max@...o.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/fs-writeback.c         |   17 +++++++++++++++++
 include/linux/writeback.h |    1 +
 2 files changed, 18 insertions(+)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1213,6 +1213,23 @@ void writeback_inodes_sb(struct super_bl
 EXPORT_SYMBOL(writeback_inodes_sb);
 
 /**
+ * writeback_inodes_sb_if_idle	-	start writeback if none underway
+ * @sb: the superblock
+ *
+ * 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)
+{
+	if (!writeback_in_progress(sb->s_bdi)) {
+		writeback_inodes_sb(sb);
+		return 1;
+	} else
+		return 0;
+}
+EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
+
+/**
  * sync_inodes_sb	-	sync sb inode pages
  * @sb: the superblock
  *
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -69,6 +69,7 @@ struct writeback_control {
 struct bdi_writeback;
 int inode_wait(void *);
 void writeback_inodes_sb(struct super_block *);
+int writeback_inodes_sb_if_idle(struct super_block *);
 void sync_inodes_sb(struct super_block *);
 void writeback_inodes_wbc(struct writeback_control *wbc);
 long wb_do_writeback(struct bdi_writeback *wb, int force_wait);


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