RE: [PATCH v5 7/7] fs/xfs: Add dax dedupe support

[ruansy.fnst@xxxxxxxxxxx]

> -----Original Message-----
> From: Darrick J. Wong <djwong@xxxxxxxxxx>
> Subject: Re: [PATCH v5 7/7] fs/xfs: Add dax dedupe support
> 
> On Tue, May 11, 2021 at 11:09:33AM +0800, Shiyang Ruan wrote:
> > Introduce xfs_mmaplock_two_inodes_and_break_dax_layout() for dax files
> > who are going to be deduped.  After that, call compare range function
> > only when files are both DAX or not.
> >
> > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> > ---
> >  fs/xfs/xfs_file.c    |  2 +-
> >  fs/xfs/xfs_inode.c   | 66
> +++++++++++++++++++++++++++++++++++++++++++-
> >  fs/xfs/xfs_inode.h   |  1 +
> >  fs/xfs/xfs_reflink.c |  4 +--
> >  4 files changed, 69 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index
> > 38d8eca05aee..bd5002d38df4 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -823,7 +823,7 @@ xfs_wait_dax_page(
> >  	xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
> >  }
> >
> > -static int
> > +int
> >  xfs_break_dax_layouts(
> >  	struct inode		*inode,
> >  	bool			*retry)
> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c index
> > 0369eb22c1bb..0774b6e2b940 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -3711,6 +3711,64 @@ xfs_iolock_two_inodes_and_break_layout(
> >  	return 0;
> >  }
> >
> > +static int
> > +xfs_mmaplock_two_inodes_and_break_dax_layout(
> > +	struct inode		*src,
> > +	struct inode		*dest)
> 
> MMAPLOCK is an xfs_inode lock, so please pass those in here.
> 
> > +{
> > +	int			error, attempts = 0;
> > +	bool			retry;
> > +	struct xfs_inode	*ip0, *ip1;
> > +	struct page		*page;
> > +	struct xfs_log_item	*lp;
> > +
> > +	if (src > dest)
> > +		swap(src, dest);
> 
> The MMAPLOCK (and ILOCK) locking order is increasing inode number, not the
> address of the incore object.  This is different (and not consistent
> with) i_rwsem/XFS_IOLOCK, but those are the rules.

Yes, I misunderstood here.

> 
> > +	ip0 = XFS_I(src);
> > +	ip1 = XFS_I(dest);
> > +
> > +again:
> > +	retry = false;
> > +	/* Lock the first inode */
> > +	xfs_ilock(ip0, XFS_MMAPLOCK_EXCL);
> > +	error = xfs_break_dax_layouts(src, &retry);
> > +	if (error || retry) {
> > +		xfs_iunlock(ip0, XFS_MMAPLOCK_EXCL);
> > +		goto again;
> > +	}
> > +
> > +	if (src == dest)
> > +		return 0;
> > +
> > +	/* Nested lock the second inode */
> > +	lp = &ip0->i_itemp->ili_item;
> > +	if (lp && test_bit(XFS_LI_IN_AIL, &lp->li_flags)) {
> > +		if (!xfs_ilock_nowait(ip1,
> > +		    xfs_lock_inumorder(XFS_MMAPLOCK_EXCL, 1))) {
> > +			xfs_iunlock(ip0, XFS_MMAPLOCK_EXCL);
> > +			if ((++attempts % 5) == 0)
> > +				delay(1); /* Don't just spin the CPU */
> > +			goto again;
> > +		}
> > +	} else
> > +		xfs_ilock(ip1, xfs_lock_inumorder(XFS_MMAPLOCK_EXCL, 1));
> > +	/*
> > +	 * We cannot use xfs_break_dax_layouts() directly here because it may
> > +	 * need to unlock & lock the XFS_MMAPLOCK_EXCL which is not suitable
> > +	 * for this nested lock case.
> > +	 */
> > +	page = dax_layout_busy_page(dest->i_mapping);
> > +	if (page) {
> > +		if (page_ref_count(page) != 1) {
> 
> This could be flattened to:
> 
> 	if (page && page_ref_count(page) != 1) {
> 		...
> 	}

OK.


--
Thanks,
Ruan Shiyang.
> 
> --D
> 
> > +			xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
> > +			xfs_iunlock(ip0, XFS_MMAPLOCK_EXCL);
> > +			goto again;
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  /*
> >   * Lock two inodes so that userspace cannot initiate I/O via file syscalls or
> >   * mmap activity.
> > @@ -3721,10 +3779,16 @@ xfs_ilock2_io_mmap(
> >  	struct xfs_inode	*ip2)
> >  {
> >  	int			ret;
> > +	struct inode		*ino1 = VFS_I(ip1);
> > +	struct inode		*ino2 = VFS_I(ip2);
> >
> > -	ret = xfs_iolock_two_inodes_and_break_layout(VFS_I(ip1), VFS_I(ip2));
> > +	ret = xfs_iolock_two_inodes_and_break_layout(ino1, ino2);
> >  	if (ret)
> >  		return ret;
> > +
> > +	if (IS_DAX(ino1) && IS_DAX(ino2))
> > +		return xfs_mmaplock_two_inodes_and_break_dax_layout(ino1, ino2);
> > +
> >  	if (ip1 == ip2)
> >  		xfs_ilock(ip1, XFS_MMAPLOCK_EXCL);
> >  	else
> > diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h index
> > ca826cfba91c..2d0b344fb100 100644
> > --- a/fs/xfs/xfs_inode.h
> > +++ b/fs/xfs/xfs_inode.h
> > @@ -457,6 +457,7 @@ enum xfs_prealloc_flags {
> >
> >  int	xfs_update_prealloc_flags(struct xfs_inode *ip,
> >  				  enum xfs_prealloc_flags flags);
> > +int	xfs_break_dax_layouts(struct inode *inode, bool *retry);
> >  int	xfs_break_layouts(struct inode *inode, uint *iolock,
> >  		enum layout_break_reason reason);
> >
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index
> > 9a780948dbd0..ff308304c5cd 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -1324,8 +1324,8 @@ xfs_reflink_remap_prep(
> >  	if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
> >  		goto out_unlock;
> >
> > -	/* Don't share DAX file data for now. */
> > -	if (IS_DAX(inode_in) || IS_DAX(inode_out))
> > +	/* Don't share DAX file data with non-DAX file. */
> > +	if (IS_DAX(inode_in) != IS_DAX(inode_out))
> >  		goto out_unlock;
> >
> >  	if (!IS_DAX(inode_in))
> > --
> > 2.31.1
> >
> >
> >