linux-ext4 - Re: [PATCH-v4 2/7] vfs: add support for a lazytime mount option

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Date:	Thu, 27 Nov 2014 18:00:16 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Linux Filesystem Development List <linux-fsdevel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Linux btrfs Developers List <linux-btrfs@...r.kernel.org>,
	XFS Developers <xfs@....sgi.com>
Subject: Re: [PATCH-v4 2/7] vfs: add support for a lazytime mount option

On Thu, Nov 27, 2014 at 02:14:21PM +0100, Jan Kara wrote:
> * change queue_io() to also call
> 	moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io, time + 24hours)
>   For this you need to tweak move_expired_inodes() to take pointer to
>   timestamp instead of pointer to work but that's trivial. Also you want
>   probably leave time ->older_than_this value (i.e. without +24 hours) if
>   we are doing WB_SYNC_ALL writeback. With this you can remove
>   flush_sb_dirty_time() completely.

Well.... it's not quite enough.  The problem is that for ext3 and
ext4, the actual work of writing the inode happens in dirty_inode(),
not in write_inode().  Which means we need to do something like this.

I'm not entirely sure whether or not this is too ugly to live;
personally, I think my hack of handling this in update_time() might be
preferable....

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index b93c529..95a42b3 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -253,7 +253,7 @@ static bool inode_dirtied_after(struct inode *inode, unsigned long t)
  */
 static int move_expired_inodes(struct list_head *delaying_queue,
 			       struct list_head *dispatch_queue,
-			       struct wb_writeback_work *work)
+			       unsigned long *older_than_this)
 {
 	LIST_HEAD(tmp);
 	struct list_head *pos, *node;
@@ -264,8 +264,8 @@ static int move_expired_inodes(struct list_head *delaying_queue,
 
 	while (!list_empty(delaying_queue)) {
 		inode = wb_inode(delaying_queue->prev);
-		if (work->older_than_this &&
-		    inode_dirtied_after(inode, *work->older_than_this))
+		if (older_than_this &&
+		    inode_dirtied_after(inode, *older_than_this))
 			break;
 		list_move(&inode->i_wb_list, &tmp);
 		moved++;
@@ -309,9 +309,14 @@ out:
 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
 {
 	int moved;
+	unsigned long one_day_later = jiffies + (HZ * 86400);
+
 	assert_spin_locked(&wb->list_lock);
 	list_splice_init(&wb->b_more_io, &wb->b_io);
-	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
+	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io,
+				    work->older_than_this);
+	moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
+				     &one_day_later);
 	trace_writeback_queue_io(wb, work, moved);
 }
 
@@ -637,6 +642,17 @@ static long writeback_sb_inodes(struct super_block *sb,
 		}
 
 		/*
+		 * If the inode is marked dirty time but is not dirty,
+		 * then at last for ext3 and ext4 we need to call
+		 * mark_inode_dirty_sync in order to get the inode
+		 * timestamp transferred to the on disk inode, since
+		 * write_inode is a no-op for those file systems.  HACK HACK HACK
+		 */
+		if ((inode->i_state & I_DIRTY_TIME) &&
+		    ((inode->i_state & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) == 0))
+			mark_inode_dirty_sync(inode);
+
+		/*
 		 * Don't bother with new inodes or inodes being freed, first
 		 * kind does not need periodic writeout yet, and for the latter
 		 * kind writeout is handled by the freer.
@@ -1233,9 +1249,10 @@ void inode_requeue_dirtytime(struct inode *inode)
 	spin_lock(&bdi->wb.list_lock);
 	spin_lock(&inode->i_lock);
 	if ((inode->i_state & I_DIRTY_WB) == 0) {
-		if (inode->i_state & I_DIRTY_TIME)
+		if (inode->i_state & I_DIRTY_TIME) {
+			inode->dirtied_when = jiffies;
 			list_move(&inode->i_wb_list, &bdi->wb.b_dirty_time);
-		else
+		} else
 			list_del_init(&inode->i_wb_list);
 	}
 	spin_unlock(&inode->i_lock);

Comments?

						- Ted
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