[PATCH 4/6] xfs: reduce the number of log forces from tail pushing

[Dave Chinner]

On Thu, Aug 25, 2011 at 03:57:06PM -0500, Alex Elder wrote:
> On Thu, 2011-08-25 at 17:17 +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner at redhat.com>
> > 
> > The AIL push code will issue a log force on ever single push loop
> > that it exits and has encountered pinned items. It doesn't rescan
> > these pinned items until it revisits the AIL from the start. Hence
> > we only need to force the log once per walk from the start of the
> > AIL to the target LSN.
> > 
> > This results in numbers like this:
> > 
> > 	xs_push_ail_flush.....         1456
> > 	xs_log_force.........          1485
> > 
> > For an 8-way 50M inode create workload - almost all the log forces
> > are coming from the AIL pushing code.
> > 
> > Reduce the number of log forces by only forcing the log if the
> > previous walk found pinned buffers. This reduces the numbers to:
> > 
> > 	xs_push_ail_flush.....          665
> > 	xs_log_force.........           682
> > 
> > For the same test.
> > 
> > Signed-off-by: Dave Chinner <dchinner at redhat.com>
> 
> This looks good to me and if you don't update it
> I can take it as-is.  A couple trivial things below
> if you decide to update.
> 
> Reviewed-by: Alex Elder <aelder at sgi.com>
> 
> > ---
> >  fs/xfs/xfs_trans_ail.c  |   28 ++++++++++++++++------------
> >  fs/xfs/xfs_trans_priv.h |    1 +
> >  2 files changed, 17 insertions(+), 12 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
> > index c15aa29..dd966e0 100644
> > --- a/fs/xfs/xfs_trans_ail.c
> > +++ b/fs/xfs/xfs_trans_ail.c
> > @@ -372,12 +372,24 @@ xfs_ail_worker(
> >  	xfs_lsn_t		lsn;
> >  	xfs_lsn_t		target;
> >  	long			tout = 10;
> > -	int			flush_log = 0;
> >  	int			stuck = 0;
> >  	int			count = 0;
> >  	int			push_xfsbufd = 0;
> >  
> > +	/*
> > +	 * If last time we ran we encountered pinned items, force the log first,
> > +	 * wait for it and then push again.
>           * and wait for it before we push it again.
>           */
> 

OK.

> > +	 */
> >  	spin_lock(&ailp->xa_lock);
> > +	if (ailp->xa_last_pushed_lsn == 0 && ailp->xa_log_flush &&
> > +	    !list_empty(&ailp->xa_ail)) {
> > +		ailp->xa_log_flush = 0;
> > +		spin_unlock(&ailp->xa_lock);
> > +		XFS_STATS_INC(xs_push_ail_flush);
> > +		xfs_log_force(mp, XFS_LOG_SYNC);
> > +		spin_lock(&ailp->xa_lock);
> > +	}
> 
> This is a definite improvement over the previous version.
> 
> > +
> >  	target = ailp->xa_target;
> >  	lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->xa_last_pushed_lsn);
> >  	if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
> > @@ -391,6 +403,7 @@ xfs_ail_worker(
> >  
> >  	XFS_STATS_INC(xs_push_ail);
> >  
> > +
> >  	/*
> >  	 * While the item we are looking at is below the given threshold
> >  	 * try to flush it out. We'd like not to stop until we've at least
> 
> Kill this hunk.

Yep, will do.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com