linux-ext4 - Re: [PATCH v2 2/2] ext2: Add locking for DAX faults

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Message-ID: <20151019124749.GG25787@quack.suse.cz>
Date:	Mon, 19 Oct 2015 14:47:49 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jan Kara <jack@...e.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Chinner <david@...morbit.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	linux-nvdimm@...ts.01.org,
	Matthew Wilcox <matthew.r.wilcox@...el.com>
Subject: Re: [PATCH v2 2/2] ext2: Add locking for DAX faults

On Wed 14-10-15 09:31:38, Ross Zwisler wrote:
> On Wed, Oct 14, 2015 at 10:51:19AM +0200, Jan Kara wrote:
> > On Tue 13-10-15 16:25:37, Ross Zwisler wrote:
> > > Add locking to ensure that DAX faults are isolated from ext2 operations
> > > that modify the data blocks allocation for an inode.  This is intended to
> > > be analogous to the work being done in XFS by Dave Chinner:
> > > 
> > > http://www.spinics.net/lists/linux-fsdevel/msg90260.html
> > > 
> > > Compared with XFS the ext2 case is greatly simplified by the fact that ext2
> > > already allocates and zeros new blocks before they are returned as part of
> > > ext2_get_block(), so DAX doesn't need to worry about getting unmapped or
> > > unwritten buffer heads.
> > > 
> > > This means that the only work we need to do in ext2 is to isolate the DAX
> > > faults from inode block allocation changes.  I believe this just means that
> > > we need to isolate the DAX faults from truncate operations.
> > > 
> > > The newly introduced dax_sem is intended to replicate the protection
> > > offered by i_mmaplock in XFS.  In addition to truncate the i_mmaplock also
> > > protects XFS operations like hole punching, fallocate down, extent
> > > manipulation IOCTLS like xfs_ioc_space() and extent swapping.  Truncate is
> > > the only one of these operations supported by ext2.
> > > 
> > > Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > 
> > The patch looks good to me. Feel free to add:
> > 
> > Reviewed-by: Jan Kara <jack@...e.com>
> > 
> > Or I can push the patch through my tree as it seems to be independent of
> > any other changes, am I right?
> > 
> > 								Honza
> 
> Yep, it is independent of other patches.  It'd be great if you pushed it up
> through your tree, thanks!

I've pulled the patch into my tree and will push it to Linus in the next
merge window.

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