Re: [PATCH v4 5/5] xfs: disable map_sync for async flush

[Pankaj Gupta <pagupta@redhat.com>]

Hi Dave,

> > Virtio pmem provides asynchronous host page cache flush
> > mechanism. we don't support 'MAP_SYNC' with virtio pmem
> > and xfs.
> > 
> > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> > ---
> >  fs/xfs/xfs_file.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index 1f2e2845eb76..dced2eb8c91a 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -1203,6 +1203,14 @@ xfs_file_mmap(
> >  	if (!IS_DAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC))
> >  		return -EOPNOTSUPP;
> >  
> > +	/* We don't support synchronous mappings with DAX files if
> > +	 * dax_device is not synchronous.
> > +	 */
> > +	if (IS_DAX(file_inode(filp)) && !dax_synchronous(
> > +		xfs_find_daxdev_for_inode(file_inode(filp))) &&
> > +					(vma->vm_flags & VM_SYNC))
> > +		return -EOPNOTSUPP;
> > +
> >  	file_accessed(filp);
> >  	vma->vm_ops = &xfs_file_vm_ops;
> >  	if (IS_DAX(file_inode(filp)))
> 
> All this ad hoc IS_DAX conditional logic is getting pretty nasty.
> 
> xfs_file_mmap(
> ....
> {
> 	struct inode	*inode = file_inode(filp);
> 
> 	if (vma->vm_flags & VM_SYNC) {
> 		if (!IS_DAX(inode))
> 			return -EOPNOTSUPP;
> 		if (!dax_synchronous(xfs_find_daxdev_for_inode(inode))
> 			return -EOPNOTSUPP;
> 	}
> 
> 	file_accessed(filp);
> 	vma->vm_ops = &xfs_file_vm_ops;
> 	if (IS_DAX(inode))
> 		vma->vm_flags |= VM_HUGEPAGE;
> 	return 0;
> }

Sure, this is better.

> 
> 
> Even better, factor out all the "MAP_SYNC supported" checks into a
> helper so that the filesystem code just doesn't have to care about
> the details of checking for DAX+MAP_SYNC support....

o.k. Will add one common helper function for both ext4 & xfs filesystems.

Thanks for the suggestion.

Best regards,
Pankaj

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