On Thu, 24 Sep 2009 15:14:15 +0800
Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> On Thu, Sep 24, 2009 at 02:54:20PM +0800, Li, Shaohua wrote:
> > __mark_inode_dirty adds inode to wb dirty list in random order. If
> > a disk has several partitions, writeback might keep spindle moving
> > between partitions. To reduce the move, better write big chunk of
> > one partition and then move to another. Inodes from one fs usually
> > are in one partion, so idealy move indoes from one fs together
> > should reduce spindle move. This patch tries to address this.
> > Before per-bdi writeback is added, the behavior is write indoes
> > from one fs first and then another, so the patch restores previous
> > behavior. The loop in the patch is a bit ugly, should we add a
> > dirty list for each superblock in bdi_writeback?
> >
> > Test in a two partition disk with attached fio script shows about
> > 3% ~ 6% improvement.
>
> Reviewed-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
>
> Good idea! The optimization looks good to me, it addresses one
> weakness of per-bdi writeback.
>
> But one problem is, Jan Kara and me are planning to remove b_io and
> hence this move_expired_inodes() function. Not sure how to do this
> optimization without b_io.
>
> > Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
> >
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index 8e1e5e1..fc87730 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -324,13 +324,29 @@ static void move_expired_inodes(struct
> > list_head *delaying_queue, struct list_head *dispatch_queue,
> > unsigned long *older_than_this)
> > {
> > + LIST_HEAD(tmp);
> > + struct list_head *pos, *node;
> > + struct super_block *sb;
> > + struct inode *inode;
> > +
> > while (!list_empty(delaying_queue)) {
> > - struct inode *inode =
> > list_entry(delaying_queue->prev,
> > - struct inode,
> > i_list);
> > + inode = list_entry(delaying_queue->prev, struct
> > inode, i_list); if (older_than_this &&
> > inode_dirtied_after(inode, *older_than_this))
> > break;
> > - list_move(&inode->i_list, dispatch_queue);
> > + list_move(&inode->i_list, &tmp);
> > + }
> > +
> > + /* Move indoes from one superblock together */
> > + while (!list_empty(&tmp)) {
> > + inode = list_entry(tmp.prev, struct inode, i_list);
> > + sb = inode->i_sb;
> > + list_for_each_prev_safe(pos, node, &tmp) {
>
> We are in spin lock, so not necessary to use the safe version?
>
safe is needed for list walks that remove entries from the list
has nothing to do with locking ;-)
--
Arjan van de Ven Intel Open Source Technology Centre
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visit http://www.lesswatts.org
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