Re: [PATCH V8 10/11] fs/xfs: Change xfs_ioctl_setattr_dax_invalidate()

From: Dave Chinner
Date: Sun Apr 19 2020 - 22:31:50 EST


On Tue, Apr 14, 2020 at 11:45:22PM -0700, ira.weiny@xxxxxxxxx wrote:
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> We only support changing FS_XFLAG_DAX on directories. Files get their
> flag from the parent directory on creation only. So no data
> invalidation needs to happen.
>
> Alter the xfs_ioctl_setattr_dax_invalidate() to be
> xfs_ioctl_setattr_dax_validate(). xfs_ioctl_setattr_dax_validate() now
> validates that any FS_XFLAG_DAX change is ok.
>
> This also allows use to remove the join_flags logic.
>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> ---
> Changes from V7:
> Use new flag_inode_dontcache()
> Skip don't cache if mount over ride is active.
>
> Changes from v6:
> Fix completely broken implementation and update commit message.
> Use the new VFS layer I_DONTCACHE to facilitate inode eviction
> and S_DAX changing on drop_caches
>
> Changes from v5:
> New patch
> ---
> fs/xfs/xfs_ioctl.c | 105 +++++++++------------------------------------
> 1 file changed, 20 insertions(+), 85 deletions(-)
>
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index c6cd92ef4a05..75d4a830ef38 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1145,63 +1145,28 @@ xfs_ioctl_setattr_xflags(
> }
>
> /*
> - * If we are changing DAX flags, we have to ensure the file is clean and any
> - * cached objects in the address space are invalidated and removed. This
> - * requires us to lock out other IO and page faults similar to a truncate
> - * operation. The locks need to be held until the transaction has been committed
> - * so that the cache invalidation is atomic with respect to the DAX flag
> - * manipulation.
> + * Mark inodes with a changing FS_XFLAG_DAX, I_DONTCACHE

That describes what the code is doing, not why.

> */
> -static int
> +static void
> xfs_ioctl_setattr_dax_invalidate(
> struct xfs_inode *ip,
> - struct fsxattr *fa,
> - int *join_flags)
> + struct fsxattr *fa)

It's not an invalidation function anymore, so needs a name change.

> - if (!(fa->fsx_xflags & FS_XFLAG_DAX) && !IS_DAX(inode))
> - return 0;
> + struct xfs_mount *mp = ip->i_mount;
> + struct inode *inode = VFS_I(ip);
>
> if (S_ISDIR(inode->i_mode))
> - return 0;
> -
> - /* lock, flush and invalidate mapping in preparation for flag change */
> - xfs_ilock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
> - error = filemap_write_and_wait(inode->i_mapping);
> - if (error)
> - goto out_unlock;
> - error = invalidate_inode_pages2(inode->i_mapping);
> - if (error)
> - goto out_unlock;
> + return;
>
> - *join_flags = XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL;
> - return 0;
> -
> -out_unlock:
> - xfs_iunlock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
> - return error;
> + if (mp->m_flags & XFS_MOUNT_DAX_ALWAYS ||
> + mp->m_flags & XFS_MOUNT_DAX_NEVER)
> + return;

if (mp->m_flags & (XFS_MOUNT_DAX_ALWAYS | XFS_MOUNT_DAX_NEVER))
return;
> + if (((fa->fsx_xflags & FS_XFLAG_DAX) &&
> + !(ip->i_d.di_flags2 & XFS_DIFLAG2_DAX)) ||
> + (!(fa->fsx_xflags & FS_XFLAG_DAX) &&
> + (ip->i_d.di_flags2 & XFS_DIFLAG2_DAX)))
> + flag_inode_dontcache(inode);

This doesn't set the XFS inode's "don't cache" flag, despite it
having one that serves exactly the same purpose. IOWs, if the
XFS_IDONTCACHE flag is now redundant, please replace it's current
usage with this new flag and get rid of the XFS inode flag. i.e.
the only place we set XFS_IDONTCACHE can be replaced with a call to
this mark_inode_dontcache() call...

Cheers,

Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx