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

Theodore Ts'o
2014-11-27T23:00:27Z

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