[PATCH 3/5] xfs: reduce ilock hold times in xfs_setattr_size

[Dave Chinner]

On Thu, Apr 19, 2012 at 04:00:44PM -0500, Ben Myers wrote:
> On Tue, Mar 27, 2012 at 10:34:48AM -0400, Christoph Hellwig wrote:
> > We do not need the ilock for most checks done in the beginning of
> > xfs_setattr_size.  Replace the long critical section before starting the
> > transaction with a smaller one around xfs_zero_eof and an optional one
> > inside xfs_qm_dqattach that isn't entered unless using quotas.  While
> > this isn't a big optimization for xfs_setattr_size itself it will allow
> > pushing the ilock into xfs_zero_eof itself later.
> > 
> > Signed-off-by: Christoph Hellwig <hch at lst.de>
> > 
> > ---
> >  fs/xfs/xfs_iops.c |   14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> > 
> > Index: xfs/fs/xfs/xfs_iops.c
> > ===================================================================
> > --- xfs.orig/fs/xfs/xfs_iops.c	2012-03-26 15:17:47.088854526 +0200
> > +++ xfs/fs/xfs/xfs_iops.c	2012-03-26 15:17:57.265521382 +0200
> > @@ -700,7 +700,7 @@ xfs_setattr_size(
> >  	xfs_off_t		oldsize, newsize;
> >  	struct xfs_trans	*tp;
> >  	int			error;
> > -	uint			lock_flags;
> > +	uint			lock_flags = 0;
> >  	uint			commit_flags = 0;
> >  
> >  	trace_xfs_setattr(ip);
> > @@ -720,10 +720,10 @@ xfs_setattr_size(
> >  			ATTR_MTIME_SET|ATTR_KILL_SUID|ATTR_KILL_SGID|
> >  			ATTR_KILL_PRIV|ATTR_TIMES_SET)) == 0);
> >  
> > -	lock_flags = XFS_ILOCK_EXCL;
> > -	if (!(flags & XFS_ATTR_NOLOCK))
> > +	if (!(flags & XFS_ATTR_NOLOCK)) {
> >  		lock_flags |= XFS_IOLOCK_EXCL;
> > -	xfs_ilock(ip, lock_flags);
> > +		xfs_ilock(ip, lock_flags);
> > +	}
> >  
> >  	oldsize = inode->i_size;
> >  	newsize = iattr->ia_size;
> 
> Usually the ilock is taken to protect i_d.di_nextents.

I don't think it matters here - we hold the IO lock exclusive and
the inode size is 0 so there can be no writes in progress nor dirty
data to write back. Hence no allocation can occur, so the extent
count cannot change, either.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com