linux-ext4 - Re: [PATCH RFC 4/8] fs/ext4: Introduce DAX inode flag

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Date:   Wed, 15 Apr 2020 13:39:25 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-kernel@...r.kernel.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        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-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC 4/8] fs/ext4: Introduce DAX inode flag

On Wed, Apr 15, 2020 at 02:08:46PM +0200, Jan Kara wrote:
> On Mon 13-04-20 21:00:26, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > Add a flag to preserve FS_XFLAG_DAX in the ext4 inode.
> > 
> > Set the flag to be user visible and changeable.  Set the flag to be
> > inherited.  Allow applications to change the flag at any time.
> > 
> > Finally, on regular files, flag the inode to not be cached to facilitate
> > changing S_DAX on the next creation of the inode.
> > 
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > ---
> >  fs/ext4/ext4.h  | 13 +++++++++----
> >  fs/ext4/ioctl.c | 21 ++++++++++++++++++++-
> >  2 files changed, 29 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index 61b37a052052..434021fcec88 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -415,13 +415,16 @@ struct flex_groups {
> >  #define EXT4_VERITY_FL			0x00100000 /* Verity protected inode */
> >  #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
> >  #define EXT4_EOFBLOCKS_FL		0x00400000 /* Blocks allocated beyond EOF */
> > +
> > +#define EXT4_DAX_FL			0x00800000 /* Inode is DAX */
> > +
> 
> You seem to be using somewhat older kernel... EXT4_EOFBLOCKS_FL doesn't
> exist anymore (but still it's good to leave it reserved for some time so
> the value you've chosen is OK).

I'm on top of 5.6 released.  Did this get removed for 5.7?  I've heard there are
some boot issues with 5.7-rc1 so I'm holding out for rc2.

> 
> > @@ -813,6 +818,17 @@ static int ext4_ioctl_get_es_cache(struct file *filp, unsigned long arg)
> >  	return error;
> >  }
> >  
> > +static void ext4_dax_dontcache(struct inode *inode, unsigned int flags)
> > +{
> > +	struct ext4_inode_info *ei = EXT4_I(inode);
> > +
> > +	if (S_ISDIR(inode->i_mode))
> > +		return;
> > +
> > +	if ((ei->i_flags ^ flags) == EXT4_DAX_FL)
> > +		inode->i_state |= I_DONTCACHE;
> > +}
> > +
> 
> You probably want to use the function you've introduced in the XFS series
> here...

you mean:

flag_inode_dontcache()
???

Yes that is done.  I sent this prior to v8 (where that was added) of the other
series...

Ira

> 
> 								Honza
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR