linux-kernel - Re: [PATCH V9 10/11] fs/xfs: Update xfs_ioctl_setattr_dax

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Message-ID: <20200421213049.GC27860@dread.disaster.area>
Date:   Wed, 22 Apr 2020 07:30:49 +1000
From:   Dave Chinner <david@...morbit.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     ira.weiny@...el.com, 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>,
        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 01:31:40PM -0700, Darrick J. Wong wrote:
> 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(...)

That doesn't seem any better. This is a preparation function now, in
that it can't fail and doesn't change the outcome of the operation
being performed. So, IMO, calling it something like
xfs_ioctl_setattr_prepare_dax() would be a better name for it.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com