[PATCH 03/13] writeback: introduce writeback_control.more_io

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

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Introduce writeback_control.more_io to indicate that more I/O is
scheduled for this wakeup of pdflush.

Note that more_io is only updated on the _visited_ superblocks,
which prevents pdflush deamons from interfering with one another.

Cc: Michael Rubin <mrubin@google.com>                                                                                   
Cc: Peter Zijlstra <peterz@infradead.org>                                                                               
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 fs/fs-writeback.c         |    6 +++++-
 include/linux/writeback.h |    1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

--- linux-mm.orig/fs/fs-writeback.c
+++ linux-mm/fs/fs-writeback.c
@@ -472,8 +472,12 @@ int generic_sync_sb_inodes(struct super_
 		iput(inode);
 		cond_resched();
 		spin_lock(&inode_lock);
-		if (wbc->nr_to_write <= 0)
+		if (wbc->nr_to_write <= 0) {
+			wbc->more_io = 1;
 			break;
+		}
+		if (!list_empty(&sb->s_more_io))
+			wbc->more_io = 1;
 	}
 	spin_unlock(&inode_lock);
 	return ret;		/* Leave any unwritten inodes on s_io */
--- linux-mm.orig/include/linux/writeback.h
+++ linux-mm/include/linux/writeback.h
@@ -62,6 +62,7 @@ struct writeback_control {
 	unsigned for_reclaim:1;		/* Invoked from the page allocator */
 	unsigned for_writepages:1;	/* This is a writepages() call */
 	unsigned range_cyclic:1;	/* range_start is cyclic */
+	unsigned more_io:1;		/* more io to be dispatched */
 };
 
 /*

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