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SubjectRe: [PATCH v4 5/5] xfs: disable map_sync for async flush
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 <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;
}


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....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com

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