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

[Pankaj Gupta]

> 
> On Thu, Apr 04, 2019 at 09:09:12AM +1100, Dave Chinner wrote:
> > On Wed, Apr 03, 2019 at 04:10:18PM +0530, Pankaj Gupta wrote:
> > > 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 <address@hidden>
> > > ---
> > >  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;
> > }
> > 
> > 
> > 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....
> 
> Seconded, since ext4 has nearly the same flag validation logic.

Agree.

Thanks,
Pankaj

> 
> --D
> 
> > 
> > Cheers,
> > 
> > Dave.
> > --
> > Dave Chinner
> > address@hidden
>