writeback: fix time ordering of the per superblock inode lists 8

Streamline the management of dirty inode lists and fix time ordering bugs.

The writeback logic used to move not-yet-expired dirty inodes from s_dirty to
s_io, *only to* move them back.  The move-inodes-back-and-forth thing is a
mess, which is eliminated by this patch.

The new scheme is:
- s_dirty acts as a time ordered io delaying queue;
- s_io/s_more_io together acts as an io dispatching queue.

On kupdate writeback, we pull some inodes from s_dirty to s_io at the start of
every full scan of s_io.  Otherwise  (i.e. for sync/throttle/background
writeback), we always pull from s_dirty on each run (a partial scan).

Note that the line
	list_splice_init(&sb->s_more_io, &sb->s_io);
is moved to queue_io() to leave s_io empty. Otherwise a big dirtied file will
sit in s_io for a long time, preventing new expired inodes to get in.

Cc: Ken Chen <kenchen@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
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 c9d105f..1f22fb5 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -119,7 +119,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                        goto out;
 
                /*
-                * If the inode was already on s_dirty or s_io, don't
+                * If the inode was already on s_dirty/s_io/s_more_io, don't
                 * reposition it (that would break s_dirty time-ordering).
                 */
                if (!was_dirty) {
@@ -173,6 +173,33 @@ static void requeue_io(struct inode *inode)
 }
 
 /*
+ * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
+ */
+static void move_expired_inodes(struct list_head *delaying_queue,
+                              struct list_head *dispatch_queue,
+                               unsigned long *older_than_this)
+{
+       while (!list_empty(delaying_queue)) {
+               struct inode *inode = list_entry(delaying_queue->prev,
+                                               struct inode, i_list);
+               if (older_than_this &&
+                       time_after(inode->dirtied_when, *older_than_this))
+                       break;
+               list_move(&inode->i_list, dispatch_queue);
+       }
+}
+
+/*
+ * Queue all expired dirty inodes for io, eldest first.
+ */
+static void queue_io(struct super_block *sb,
+                               unsigned long *older_than_this)
+{
+       list_splice_init(&sb->s_more_io, sb->s_io.prev);
+       move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
+}
+
+/*
  * Write a single inode's dirty pages and inode data out to disk.
  * If `wait' is set, wait on the writeout.
  *
@@ -222,7 +249,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
                        /*
                         * We didn't write back all the pages.  nfs_writepages()
                         * sometimes bales out without doing anything. Redirty
-                        * the inode.  It is moved from s_io onto s_dirty.
+                        * the inode; Move it from s_io onto s_more_io/s_dirty.
                         */
                        /*
                         * akpm: if the caller was the kupdate function we put
@@ -235,10 +262,9 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
                         */
                        if (wbc->for_kupdate) {
                                /*
-                                * For the kupdate function we leave the inode
-                                * at the head of sb_dirty so it will get more
-                                * writeout as soon as the queue becomes
-                                * uncongested.
+                                * For the kupdate function we move the inode
+                                * to s_more_io so it will get more writeout as
+                                * soon as the queue becomes uncongested.
                                 */
                                inode->i_state |= I_DIRTY_PAGES;
                                requeue_io(inode);
@@ -296,10 +322,10 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 
                /*
                 * We're skipping this inode because it's locked, and we're not
-                * doing writeback-for-data-integrity.  Move it to the head of
-                * s_dirty so that writeback can proceed with the other inodes
-                * on s_io.  We'll have another go at writing back this inode
-                * when the s_dirty iodes get moved back onto s_io.
+                * doing writeback-for-data-integrity.  Move it to s_more_io so
+                * that writeback can proceed with the other inodes on s_io.
+                * We'll have another go at writing back this inode when we
+                * completed a full scan of s_io.
                 */
                requeue_io(inode);
 
@@ -366,7 +392,7 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
        const unsigned long start = jiffies;    /* livelock avoidance */
 
        if (!wbc->for_kupdate || list_empty(&sb->s_io))
-               list_splice_init(&sb->s_dirty, &sb->s_io);
+               queue_io(sb, wbc->older_than_this);
 
        while (!list_empty(&sb->s_io)) {
                struct inode *inode = list_entry(sb->s_io.prev,
@@ -411,13 +437,6 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
                if (time_after(inode->dirtied_when, start))
                        break;
 
-               /* Was this inode dirtied too recently? */
-               if (wbc->older_than_this && time_after(inode->dirtied_when,
-                                               *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))
                        break;
@@ -446,10 +465,6 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
                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 */
 }
 
@@ -459,7 +474,7 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
  * Note:
  * We don't need to grab a reference to superblock here. If it has non-empty
  * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
- * past sync_inodes_sb() until both the ->s_dirty and ->s_io lists are
+ * past sync_inodes_sb() until the ->s_dirty/s_io/s_more_io lists are all
  * empty. Since __sync_single_inode() regains inode_lock before it finally moves
  * inode from superblock lists we are OK.
  *