Message-ID: <20200421203140.GD6742@magnolia>
Date:   Tue, 21 Apr 2020 13:31:40 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V9 10/11] fs/xfs: Update
 xfs_ioctl_setattr_dax_invalidate()

On Tue, Apr 21, 2020 at 12:17:52PM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Because of the separation of FS_XFLAG_DAX from S_DAX and the delayed
> setting of S_DAX, data invalidation no longer needs to happen when
> FS_XFLAG_DAX is changed.
> 
> Change xfs_ioctl_setattr_dax_invalidate() to be
> xfs_ioctl_dax_check_set_cache() and alter the code to reflect the new
> functionality.
> 
> Furthermore, we no longer need the locking so we remove the join_flags
> logic.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> ---
> Changes from V8:
> 	Change name of function to xfs_ioctl_dax_check_set_cache()
> 	Update commit message
> 	Fix bit manipulations
> 
> 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 | 108 +++++++++------------------------------------
>  1 file changed, 20 insertions(+), 88 deletions(-)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 104495ac187c..b87b571a6748 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1245,64 +1245,26 @@ xfs_ioctl_setattr_xflags(
>  	return 0;
>  }
>  
> -/*
> - * 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.
> - */
> -static int
> -xfs_ioctl_setattr_dax_invalidate(
> +static void
> +xfs_ioctl_dax_check_set_cache(

That's a ... strange name.  Set cache on what?

Oh, this is the function that sets I_DONTCACHE if an FS_XFLAG_DAX change
could have an immediate effect on S_DAX (assuming no other users).  What
do you think of the following?

	/*
	 * If a change to FS_XFLAG_DAX will result in an change to S_DAX
	 * the next time the incore inode is initialized, set the VFS
	 * I_DONTCACHE flag to try to hurry that along.
	 */
	static void
	xfs_ioctl_try_change_vfs_dax(...)

--D

>  	struct xfs_inode	*ip,
> -	struct fsxattr		*fa,
> -	int			*join_flags)
> +	struct fsxattr		*fa)
>  {
> -	struct inode		*inode = VFS_I(ip);
> -	struct super_block	*sb = inode->i_sb;
> -	int			error;
> -
> -	*join_flags = 0;
> -
> -	/*
> -	 * It is only valid to set the DAX flag on regular files and
> -	 * directories on filesystems where the block size is equal to the page
> -	 * size. On directories it serves as an inherited hint so we don't
> -	 * have to check the device for dax support or flush pagecache.
> -	 */
> -	if (fa->fsx_xflags & FS_XFLAG_DAX) {
> -		struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
> -
> -		if (!bdev_dax_supported(target->bt_bdev, sb->s_blocksize))
> -			return -EINVAL;
> -	}
> -
> -	/* If the DAX state is not changing, we have nothing to do here. */
> -	if ((fa->fsx_xflags & FS_XFLAG_DAX) && IS_DAX(inode))
> -		return 0;
> -	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;
> -
> -	*join_flags = XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL;
> -	return 0;
> +		return;
>  
> -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 (((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)))
> +		mark_inode_dontcache(inode);
>  }
>  
>  /*
> @@ -1310,17 +1272,10 @@ xfs_ioctl_setattr_dax_invalidate(
>   * have permission to do so. On success, return a clean transaction and the
>   * inode locked exclusively ready for further operation specific checks. On
>   * failure, return an error without modifying or locking the inode.
> - *
> - * The inode might already be IO locked on call. If this is the case, it is
> - * indicated in @join_flags and we take full responsibility for ensuring they
> - * are unlocked from now on. Hence if we have an error here, we still have to
> - * unlock them. Otherwise, once they are joined to the transaction, they will
> - * be unlocked on commit/cancel.
>   */
>  static struct xfs_trans *
>  xfs_ioctl_setattr_get_trans(
> -	struct xfs_inode	*ip,
> -	int			join_flags)
> +	struct xfs_inode	*ip)
>  {
>  	struct xfs_mount	*mp = ip->i_mount;
>  	struct xfs_trans	*tp;
> @@ -1337,8 +1292,7 @@ xfs_ioctl_setattr_get_trans(
>  		goto out_unlock;
>  
>  	xfs_ilock(ip, XFS_ILOCK_EXCL);
> -	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL | join_flags);
> -	join_flags = 0;
> +	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
>  
>  	/*
>  	 * CAP_FOWNER overrides the following restrictions:
> @@ -1359,8 +1313,6 @@ xfs_ioctl_setattr_get_trans(
>  out_cancel:
>  	xfs_trans_cancel(tp);
>  out_unlock:
> -	if (join_flags)
> -		xfs_iunlock(ip, join_flags);
>  	return ERR_PTR(error);
>  }
>  
> @@ -1486,7 +1438,6 @@ xfs_ioctl_setattr(
>  	struct xfs_dquot	*pdqp = NULL;
>  	struct xfs_dquot	*olddquot = NULL;
>  	int			code;
> -	int			join_flags = 0;
>  
>  	trace_xfs_ioctl_setattr(ip);
>  
> @@ -1510,18 +1461,9 @@ xfs_ioctl_setattr(
>  			return code;
>  	}
>  
> -	/*
> -	 * Changing DAX config may require inode locking for mapping
> -	 * invalidation. These need to be held all the way to transaction commit
> -	 * or cancel time, so need to be passed through to
> -	 * xfs_ioctl_setattr_get_trans() so it can apply them to the join call
> -	 * appropriately.
> -	 */
> -	code = xfs_ioctl_setattr_dax_invalidate(ip, fa, &join_flags);
> -	if (code)
> -		goto error_free_dquots;
> +	xfs_ioctl_dax_check_set_cache(ip, fa);
>  
> -	tp = xfs_ioctl_setattr_get_trans(ip, join_flags);
> +	tp = xfs_ioctl_setattr_get_trans(ip);
>  	if (IS_ERR(tp)) {
>  		code = PTR_ERR(tp);
>  		goto error_free_dquots;
> @@ -1651,7 +1593,6 @@ xfs_ioc_setxflags(
>  	struct fsxattr		fa;
>  	struct fsxattr		old_fa;
>  	unsigned int		flags;
> -	int			join_flags = 0;
>  	int			error;
>  
>  	if (copy_from_user(&flags, arg, sizeof(flags)))
> @@ -1668,18 +1609,9 @@ xfs_ioc_setxflags(
>  	if (error)
>  		return error;
>  
> -	/*
> -	 * Changing DAX config may require inode locking for mapping
> -	 * invalidation. These need to be held all the way to transaction commit
> -	 * or cancel time, so need to be passed through to
> -	 * xfs_ioctl_setattr_get_trans() so it can apply them to the join call
> -	 * appropriately.
> -	 */
> -	error = xfs_ioctl_setattr_dax_invalidate(ip, &fa, &join_flags);
> -	if (error)
> -		goto out_drop_write;
> +	xfs_ioctl_dax_check_set_cache(ip, &fa);
>  
> -	tp = xfs_ioctl_setattr_get_trans(ip, join_flags);
> +	tp = xfs_ioctl_setattr_get_trans(ip);
>  	if (IS_ERR(tp)) {
>  		error = PTR_ERR(tp);
>  		goto out_drop_write;
> -- 
> 2.25.1
> 

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