[PATCH 6/6] writeback: introduce writeback_control.inodes_written

[Wu Fengguang]

Introduce writeback_control.inodes_written to count successful
->write_inode() calls.  A non-zero value means there are some
progress on writeback, in which case more writeback will be tried.

This prevents aborting a background writeback work prematually when
the current set of inodes for IO happen to be metadata-only dirty.

Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/fs-writeback.c         |    5 +++++
 include/linux/writeback.h |    1 +
 2 files changed, 6 insertions(+)

--- linux-next.orig/fs/fs-writeback.c	2010-07-22 13:07:54.000000000 +0800
+++ linux-next/fs/fs-writeback.c	2010-07-22 13:07:58.000000000 +0800
@@ -379,6 +379,8 @@ writeback_single_inode(struct inode *ino
 		int err = write_inode(inode, wbc);
 		if (ret == 0)
 			ret = err;
+		if (!err)
+			wbc->inodes_written++;
 	}
 
 	spin_lock(&inode_lock);
@@ -628,6 +630,7 @@ static long wb_writeback(struct bdi_writ
 
 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 		wbc.pages_skipped = 0;
+		wbc.inodes_written = 0;
 
 		trace_wbc_writeback_start(&wbc, wb->bdi);
 		if (work->sb)
@@ -650,6 +653,8 @@ static long wb_writeback(struct bdi_writ
 		 */
 		if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)
 			continue;
+		if (wbc.inodes_written)
+			continue;
 
 		/*
 		 * Nothing written and no more inodes for IO, bail
--- linux-next.orig/include/linux/writeback.h	2010-07-22 11:24:46.000000000 +0800
+++ linux-next/include/linux/writeback.h	2010-07-22 13:07:58.000000000 +0800
@@ -34,6 +34,7 @@ struct writeback_control {
 	long nr_to_write;		/* Write this many pages, and decrement
 					   this for each page written */
 	long pages_skipped;		/* Pages which were not written */
+	long inodes_written;		/* Number of inodes(metadata) synced */
 
 	/*
 	 * For a_ops->writepages(): is start or end are non-zero then this is


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