On Mon, Jul 26, 2010 at 09:11:52PM +0800, Wu Fengguang wrote:
> On Mon, Jul 26, 2010 at 08:59:55PM +0800, Mel Gorman wrote:
> > On Mon, Jul 26, 2010 at 08:56:35PM +0800, Wu Fengguang wrote:
> > > > > @@ -232,8 +232,15 @@ static void move_expired_inodes(struct l
> > > > > while (!list_empty(delaying_queue)) {
> > > > > inode = list_entry(delaying_queue->prev, struct inode, i_list);
> > > > > if (expire_interval &&
> > > > > - inode_dirtied_after(inode, older_than_this))
> > > > > - break;
> > > > > + inode_dirtied_after(inode, older_than_this)) {
> > > > > + if (wbc->for_background &&
> > > > > + list_empty(dispatch_queue) && list_empty(&tmp)) {
> > > > > + expire_interval >>= 1;
> > > > > + older_than_this = jiffies - expire_interval;
> > > > > + continue;
> > > > > + } else
> > > > > + break;
> > > > > + }
> > > >
> > > > This needs a comment.
> > > >
> > > > I think what it is saying is that if background flush is active but no
> > > > inodes are old enough, consider newer inodes. This is on the assumption
> > > > that page reclaim has encountered dirty pages and the dirty inodes are
> > > > still too young.
> > >
> > > Yes this should be commented. How about this one?
> > >
> > > @@ -232,8 +232,20 @@ static void move_expired_inodes(struct l
> > > while (!list_empty(delaying_queue)) {
> > > inode = list_entry(delaying_queue->prev, struct inode, i_list);
> > > if (expire_interval &&
> > > - inode_dirtied_after(inode, older_than_this))
> > > + inode_dirtied_after(inode, older_than_this)) {
> > > + /*
> > > + * background writeback will start with expired inodes,
> > > + * and then fresh inodes. This order helps reducing
> > > + * the number of dirty pages reaching the end of LRU
> > > + * lists and cause trouble to the page reclaim.
> > > + */
> >
> > s/reducing/reduce/
> >
> > Otherwise, it's enough detail to know what is going on. Thanks
>
> Thanks. Here is the updated patch.
> ---
> Subject: writeback: sync expired inodes first in background writeback
> From: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> Date: Wed Jul 21 20:11:53 CST 2010
>
> A background flush work may run for ever. So it's reasonable for it to
> mimic the kupdate behavior of syncing old/expired inodes first.
>
> The policy is
> - enqueue all newly expired inodes at each queue_io() time
> - enqueue all dirty inodes if there are no more expired inodes to sync
>
> This will help reduce the number of dirty pages encountered by page
> reclaim, eg. the pageout() calls. Normally older inodes contain older
> dirty pages, which are more close to the end of the LRU lists. So
> syncing older inodes first helps reducing the dirty pages reached by
> the page reclaim code.
>
> CC: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Acked-by: Mel Gorman <mel@xxxxxxxxx>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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