writeback: fix periodic superblock dirty inode flushing
Current -mm tree has bucketful of bug fixes in periodic writeback path.
However, we still hit a glitch where dirty pages on a given inode aren't
completely flushed to the disk, and system will accumulate large amount of
dirty pages beyond what dirty_expire_interval is designed for.
The problem is __sync_single_inode() will move an inode to sb->s_dirty list
even when there are more pending dirty pages on that inode. If there is
another inode with a small number of dirty pages, we hit a case where the loop
iteration in wb_kupdate() terminates prematurely because wbc.nr_to_write > 0.
Thus leaving the inode that has large amount of dirty pages behind and it has
to wait for another dirty_writeback_interval before we flush it again. We
effectively only write out MAX_WRITEBACK_PAGES every dirty_writeback_interval.
If the rate of dirtying is sufficiently high, the system will start
accumulate a large number of dirty pages.
So fix it by having another sb->s_more_io list on which to park the inode
while we iterate through sb->s_io and to allow each dirty inode which resides
on that sb to have an equal chance of flushing some amount of dirty pages.
Signed-off-by: Ken Chen <kenchen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 39fadfa..c9d105f 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -165,25 +165,11 @@
}
/*
- * Redirty an inode, but mark it as the very next-to-be-written inode on its
- * superblock's dirty-inode list.
- * We need to preserve s_dirty's reverse-time-orderedness, so we cheat by
- * setting this inode's dirtied_when to the same value as that of the inode
- * which is presently head-of-list, if present head-of-list is newer than this
- * inode. (head-of-list is the least-recently-dirtied inode: the oldest one).
+ * requeue inode for re-scanning after sb->s_io list is exhausted.
*/
-static void redirty_head(struct inode *inode)
+static void requeue_io(struct inode *inode)
{
- struct super_block *sb = inode->i_sb;
-
- if (!list_empty(&sb->s_dirty)) {
- struct inode *head_inode;
-
- head_inode = list_entry(sb->s_dirty.prev, struct inode, i_list);
- if (time_after(inode->dirtied_when, head_inode->dirtied_when))
- inode->dirtied_when = head_inode->dirtied_when;
- }
- list_move_tail(&inode->i_list, &sb->s_dirty);
+ list_move(&inode->i_list, &inode->i_sb->s_more_io);
}
/*
@@ -255,7 +241,7 @@
* uncongested.
*/
inode->i_state |= I_DIRTY_PAGES;
- redirty_head(inode);
+ requeue_io(inode);
} else {
/*
* Otherwise fully redirty the inode so that
@@ -315,7 +301,7 @@
* on s_io. We'll have another go at writing back this inode
* when the s_dirty iodes get moved back onto s_io.
*/
- redirty_head(inode);
+ requeue_io(inode);
/*
* Even if we don't actually write the inode itself here,
@@ -410,14 +396,14 @@
wbc->encountered_congestion = 1;
if (!sb_is_blkdev_sb(sb))
break; /* Skip a congested fs */
- redirty_head(inode);
+ requeue_io(inode);
continue; /* Skip a congested blockdev */
}
if (wbc->bdi && bdi != wbc->bdi) {
if (!sb_is_blkdev_sb(sb))
break; /* fs has the wrong queue */
- redirty_head(inode);
+ requeue_io(inode);
continue; /* blockdev has wrong queue */
}
@@ -427,8 +413,10 @@
/* Was this inode dirtied too recently? */
if (wbc->older_than_this && time_after(inode->dirtied_when,
- *wbc->older_than_this))
+ *wbc->older_than_this)) {
+ list_splice_init(&sb->s_io, sb->s_dirty.prev);
break;
+ }
/* Is another pdflush already flushing this queue? */
if (current_is_pdflush() && !writeback_acquire(bdi))
@@ -458,6 +446,10 @@
if (wbc->nr_to_write <= 0)
break;
}
+
+ if (list_empty(&sb->s_io))
+ list_splice_init(&sb->s_more_io, &sb->s_io);
+
return; /* Leave any unwritten inodes on s_io */
}
diff --git a/fs/super.c b/fs/super.c
index fc8ebed..1bfcca2 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -67,6 +67,7 @@
}
INIT_LIST_HEAD(&s->s_dirty);
INIT_LIST_HEAD(&s->s_io);
+ INIT_LIST_HEAD(&s->s_more_io);
INIT_LIST_HEAD(&s->s_files);
INIT_LIST_HEAD(&s->s_instances);
INIT_HLIST_HEAD(&s->s_anon);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 30aca33..0b38a89 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1002,6 +1002,7 @@
struct list_head s_inodes; /* all inodes */
struct list_head s_dirty; /* dirty inodes */
struct list_head s_io; /* parked for writeback */
+ struct list_head s_more_io; /* parked for more writeback */
struct hlist_head s_anon; /* anonymous dentries for (nfs) exporting */
struct list_head s_files;