Re: [PATCH 4/5] xfs: drop inactive dquots before inactivating inodes

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Jun 01, 2021 at 10:35:06AM +1000, Dave Chinner wrote:
> On Mon, May 31, 2021 at 03:41:13PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > During quotaoff, the incore inode scan to detach dquots from inodes
> > won't touch inodes that have lost their VFS state but haven't yet been
> > queued for reclaim.  This isn't strictly a problem because we drop the
> > dquots at the end of inactivation, but if we detect this situation
> > before starting inactivation, we can drop the inactive dquots early to
> > avoid delaying quotaoff further.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > ---
> >  fs/xfs/xfs_super.c |   32 ++++++++++++++++++++++++++++----
> >  1 file changed, 28 insertions(+), 4 deletions(-)
> > 
> > 
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index a2dab05332ac..79f1cd1a0221 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -637,22 +637,46 @@ xfs_fs_destroy_inode(
> >  	struct inode		*inode)
> >  {
> >  	struct xfs_inode	*ip = XFS_I(inode);
> > +	struct xfs_mount	*mp = ip->i_mount;
> >  
> >  	trace_xfs_destroy_inode(ip);
> >  
> >  	ASSERT(!rwsem_is_locked(&inode->i_rwsem));
> > -	XFS_STATS_INC(ip->i_mount, vn_rele);
> > -	XFS_STATS_INC(ip->i_mount, vn_remove);
> > +	XFS_STATS_INC(mp, vn_rele);
> > +	XFS_STATS_INC(mp, vn_remove);
> > +
> > +	/*
> > +	 * If a quota type is turned off but we still have a dquot attached to
> > +	 * the inode, detach it before processing this inode to avoid delaying
> > +	 * quotaoff for longer than is necessary.
> > +	 *
> > +	 * The inode has no VFS state and hasn't been tagged for any kind of
> > +	 * reclamation, which means that iget, quotaoff, blockgc, and reclaim
> > +	 * will not touch it.  It is therefore safe to do this locklessly
> > +	 * because we have the only reference here.
> > +	 */
> > +	if (!XFS_IS_UQUOTA_ON(mp)) {
> > +		xfs_qm_dqrele(ip->i_udquot);
> > +		ip->i_udquot = NULL;
> > +	}
> > +	if (!XFS_IS_GQUOTA_ON(mp)) {
> > +		xfs_qm_dqrele(ip->i_gdquot);
> > +		ip->i_gdquot = NULL;
> > +	}
> > +	if (!XFS_IS_PQUOTA_ON(mp)) {
> > +		xfs_qm_dqrele(ip->i_pdquot);
> > +		ip->i_pdquot = NULL;
> > +	}
> >  
> >  	xfs_inactive(ip);
> 
> Shouldn't we just make xfs_inactive() unconditionally detatch dquots
> rather than just in the conditional case it does now after attaching
> dquots because it has to make modifications? For inodes that don't
> require any inactivation work, we get the same thing, and for those
> that do running a few extra transactions before dropping the dquots
> isn't going to make a huge difference to the quotaoff latency....

Actually... the previous patch does exactly that.  I'll drop this patch.

--D

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com