Re: [RFC PATCH 2/2] xfs_export_operations.commit_metadata

Re: [RFC PATCH 2/2] xfs_export_operations.commit_metadata

[Christoph Hellwig]

On Tue, Feb 09, 2010 at 06:33:37PM -0600, Ben Myers wrote:
> Here is the commit_metadata export_operation for xfs.  We take two dentries and
> force the log up to the larger lsn.  It looks to me that in nfsd the child is
> always modified after the parent so generally we expect the child's lsn to be
> larger.  If that's not the case we'll just force the entire thing.
> 
> The basic form of this is based upon one of Christoph's suggestions.  I'm an
> xfs newbie so I'm not very comfortable with it yet.  My understanding is that I
> need to verify that all of the necessary changes make it into the transations
> we're forcing into the log here.  I am still looking into that and hopefully
> the XFS gurus can continue to provide guidance.

Ccing the xfs list would help with that :)  Anyway, I think it looks
pretty good, but there's quite a few smaller nitpicks:

> +STATIC int
> +xfs_fs_nfs_commit_metadata(
> +	struct dentry		*parent,
> +	struct dentry		*child)
> +{
> +	struct xfs_inode	*p_xip = NULL, *c_xip = NULL;

Normal xfs naming would be dp for the parent, and ip for the child,
it would be good to stick to that.

> +	struct xfs_mount	*i_mount = NULL;	

Normal name all over xfs would be mp.

> +	} else if (parent && child) {
> +		p_xip = XFS_I(parent->d_inode);
> +		c_xip = XFS_I(child->d_inode);
> +		xfs_ilock(p_xip, XFS_ILOCK_SHARED);
> +		xfs_ilock(c_xip, XFS_ILOCK_SHARED);

If we need to lock both parent and child we need to use
xfs_lock_two_inodes to make sure the lock order is correct.

> +		if (xfs_ipincount(c_xip)) {
> +			/*
> +			 * AFAICS the child is always modified after the parent
> +			 * in nfsd so should always have a larger lsn.
> +			 */
> +			if (c_xip->i_itemp->ili_last_lsn > force_lsn) {
> +				force_lsn = c_xip->i_itemp->ili_last_lsn;
> +			} else {
> +				force_lsn = 0; /* whole thing */
> +			}

I wouldn't rely on that and always take the larger one.


Now with the simplification of always having a non-zero first argument
suggested in the previous mail this might be simplified down to:

STATIC int
xfs_fs_nfs_commit_metadata(
	struct dentry		*parent,
	struct dentry		*child)
{
	struct xfs_inode	*dp = XFS_I(parent->d_inode);
	struct xfs_inode	*ip = NULL;
	struct xfs_mount	*mp = dp->i_mount;
	xfs_lsn_t		force_lsn = 0;
	int			error = 0;

	if (child) {
		ip = XFS_I(child->d_inode);
		xfs_lock_two_inodes(dp, ip, XFS_ILOCK_SHARED);
	} else {
		xfs_ilock(dp, XFS_ILOCK_SHARED);
	}

	if (xfs_ipincount(dp))
		force_lsn = dp->i_itemp->ili_last_lsn;
	if (ip && xfs_ipincount(ip))
		force_lsn = max(force_lsn, ip->i_itemp->ili_last_lsn);

	error = _xfs_log_force_lsn(mp, force_lsn, NULL);

	if (ip)
		xfs_iunlock(ip, XFS_ILOCK_SHARED);
	xfs_iunlock(dp, XFS_ILOCK_SHARED);

	return error;
}

Note that _xfs_log_force_lsn is new in the XFS tree, mainline still
has _xfs_log_force with an lsn argument.

Also note that ->commit_metadata probably should take just two inodes
instead of two dentires given the level it operates on, but it shouldn't
matter too much.

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Re: [RFC PATCH 2/2] xfs_export_operations.commit_metadata

[Christoph Hellwig]

On Wed, Feb 10, 2010 at 04:07:50AM -0500, Christoph Hellwig wrote:
> > +			/*
> > +			 * AFAICS the child is always modified after the parent
> > +			 * in nfsd so should always have a larger lsn.
> > +			 */
> > +			if (c_xip->i_itemp->ili_last_lsn > force_lsn) {
> > +				force_lsn = c_xip->i_itemp->ili_last_lsn;
> > +			} else {
> > +				force_lsn = 0; /* whole thing */
> > +			}
> 
> I wouldn't rely on that and always take the larger one.

Or we could use that fact for making the prototype saner:

 - the commit_metadata only takes a single inode to force out
 - we make sure to always call in on the child first.  For any
   log based filesystem that will force the parent update, too.
 - we then call it on the parent, which will be a no-op and thus
   fast for a log based filesystem, but still provide a fallback
   if that is not the case.

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Re: [RFC PATCH 2/2] xfs_export_operations.commit_metadata

[bpm]

Howdy,

On Wed, Feb 10, 2010 at 04:07:50AM -0500, Christoph Hellwig wrote:
> On Tue, Feb 09, 2010 at 06:33:37PM -0600, Ben Myers wrote:
> > hopefully
> > the XFS gurus can continue to provide guidance.
> 
> Ccing the xfs list would help with that :) 

I'll cross-post the next rev.  ;)

> > +		if (xfs_ipincount(c_xip)) {
> > +			/*
> > +			 * AFAICS the child is always modified after the parent
> > +			 * in nfsd so should always have a larger lsn.
> > +			 */
> > +			if (c_xip->i_itemp->ili_last_lsn > force_lsn) {
> > +				force_lsn = c_xip->i_itemp->ili_last_lsn;
> > +			} else {
> > +				force_lsn = 0; /* whole thing */
> > +			}
> 
> I wouldn't rely on that and always take the larger one.

I am concerned that ili_last_lsn will roll over at some point.  I
haven't figured out how to detect that yet.
 
> Now with the simplification of always having a non-zero first argument
> suggested in the previous mail this might be simplified down to:
> 
> STATIC int
> xfs_fs_nfs_commit_metadata(
> 	struct dentry		*parent,
> 	struct dentry		*child)
> {
> 	struct xfs_inode	*dp = XFS_I(parent->d_inode);
> 	struct xfs_inode	*ip = NULL;
> 	struct xfs_mount	*mp = dp->i_mount;
> 	xfs_lsn_t		force_lsn = 0;
> 	int			error = 0;
> 
> 	if (child) {
> 		ip = XFS_I(child->d_inode);
> 		xfs_lock_two_inodes(dp, ip, XFS_ILOCK_SHARED);
> 	} else {
> 		xfs_ilock(dp, XFS_ILOCK_SHARED);
> 	}
> 
> 	if (xfs_ipincount(dp))
> 		force_lsn = dp->i_itemp->ili_last_lsn;
> 	if (ip && xfs_ipincount(ip))
> 		force_lsn = max(force_lsn, ip->i_itemp->ili_last_lsn);
> 
+	if (force_lsn)
>	 	error = _xfs_log_force_lsn(mp, force_lsn, NULL);
> 
> 	if (ip)
> 		xfs_iunlock(ip, XFS_ILOCK_SHARED);
> 	xfs_iunlock(dp, XFS_ILOCK_SHARED);
> 
> 	return error;
> }

That's nice!

> Note that _xfs_log_force_lsn is new in the XFS tree, mainline still
> has _xfs_log_force with an lsn argument.

I've been working with Bruce's tree.  Not sure how best to handle that.

Thanks,
	Ben

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Re: [RFC PATCH 2/2] xfs_export_operations.commit_metadata

[Dave Chinner]

On Wed, Feb 10, 2010 at 02:15:27PM -0600, bpm@sgi.com wrote:
> Howdy,
> 
> On Wed, Feb 10, 2010 at 04:07:50AM -0500, Christoph Hellwig wrote:
> > On Tue, Feb 09, 2010 at 06:33:37PM -0600, Ben Myers wrote:
> > > hopefully
> > > the XFS gurus can continue to provide guidance.
> > 
> > Ccing the xfs list would help with that :) 
> 
> I'll cross-post the next rev.  ;)
> 
> > > +		if (xfs_ipincount(c_xip)) {
> > > +			/*
> > > +			 * AFAICS the child is always modified after the parent
> > > +			 * in nfsd so should always have a larger lsn.
> > > +			 */
> > > +			if (c_xip->i_itemp->ili_last_lsn > force_lsn) {
> > > +				force_lsn = c_xip->i_itemp->ili_last_lsn;
> > > +			} else {
> > > +				force_lsn = 0; /* whole thing */
> > > +			}
> > 
> > I wouldn't rely on that and always take the larger one.
> 
> I am concerned that ili_last_lsn will roll over at some point.  I
> haven't figured out how to detect that yet.

XFS_LSN_CMP() should be used for LSN comparisons - it handles
rollover corectly.


> > Now with the simplification of always having a non-zero first argument
> > suggested in the previous mail this might be simplified down to:
> > 
> > STATIC int
> > xfs_fs_nfs_commit_metadata(
> > 	struct dentry		*parent,
> > 	struct dentry		*child)
> > {
> > 	struct xfs_inode	*dp = XFS_I(parent->d_inode);
> > 	struct xfs_inode	*ip = NULL;
> > 	struct xfs_mount	*mp = dp->i_mount;
> > 	xfs_lsn_t		force_lsn = 0;
> > 	int			error = 0;
> > 
> > 	if (child) {
> > 		ip = XFS_I(child->d_inode);
> > 		xfs_lock_two_inodes(dp, ip, XFS_ILOCK_SHARED);
> > 	} else {
> > 		xfs_ilock(dp, XFS_ILOCK_SHARED);
> > 	}
> > 
> > 	if (xfs_ipincount(dp))
> > 		force_lsn = dp->i_itemp->ili_last_lsn;
> > 	if (ip && xfs_ipincount(ip))
> > 		force_lsn = max(force_lsn, ip->i_itemp->ili_last_lsn);

So this should be:

		if (XFS_LSN_CMP(force_lsn, ip->i_itemp->ili_last_lsn) < 0)
			force_lsn = ip->i_itemp->ili_last_lsn;

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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Re: [RFC PATCH 2/2] xfs_export_operations.commit_metadata

[Christoph Hellwig]

On Wed, Feb 10, 2010 at 02:15:27PM -0600, bpm@sgi.com wrote:
> > Note that _xfs_log_force_lsn is new in the XFS tree, mainline still
> > has _xfs_log_force with an lsn argument.
> 
> I've been working with Bruce's tree.  Not sure how best to handle that.

Keep working against it for now, the merge fixup will be easy enough.

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