linux-kernel - Re: [PATCH v3 2/6] ext2, ext4: only set S

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Date:	Wed, 17 Feb 2016 22:33:25 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Theodore Ts'o <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	Jens Axboe <axboe@...nel.dk>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-block@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-nvdimm@...ts.01.org, xfs@....sgi.com
Subject: Re: [PATCH v3 2/6] ext2, ext4: only set S_DAX for regular inodes

On Tue 16-02-16 20:34:15, Ross Zwisler wrote:
> When S_DAX is set on an inode we assume that if there are pages attached
> to the mapping (mapping->nrpages != 0), those pages are clean zero pages
> that were used to service reads from holes.  Any dirty data associated with
> the inode should be in the form of DAX exceptional entries
> (mapping->nrexceptional) that is written back via
> dax_writeback_mapping_range().
> 
> With the current code, though, this isn't always true.  For example, ext2
> and ext4 directory inodes can have S_DAX set, but have their dirty data
> stored as dirty page cache entries.  For these types of inodes, having
> S_DAX set doesn't really make sense since their I/O doesn't actually happen
> through the DAX code path.
> 
> Instead, only allow S_DAX to be set for regular inodes for ext2 and ext4.
> This allows us to have strict DAX vs non-DAX paths in the writeback code.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext2/inode.c | 2 +-
>  fs/ext4/inode.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index 338eefd..27e2cdd 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -1296,7 +1296,7 @@ void ext2_set_inode_flags(struct inode *inode)
>  		inode->i_flags |= S_NOATIME;
>  	if (flags & EXT2_DIRSYNC_FL)
>  		inode->i_flags |= S_DIRSYNC;
> -	if (test_opt(inode->i_sb, DAX))
> +	if (test_opt(inode->i_sb, DAX) && S_ISREG(inode->i_mode))
>  		inode->i_flags |= S_DAX;
>  }
>  
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 83bc8bf..7088aa5 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4127,7 +4127,7 @@ void ext4_set_inode_flags(struct inode *inode)
>  		new_fl |= S_NOATIME;
>  	if (flags & EXT4_DIRSYNC_FL)
>  		new_fl |= S_DIRSYNC;
> -	if (test_opt(inode->i_sb, DAX))
> +	if (test_opt(inode->i_sb, DAX) && S_ISREG(inode->i_mode))
>  		new_fl |= S_DAX;
>  	inode_set_flags(inode, new_fl,
>  			S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC|S_DAX);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR