linux-ext4 - Re: [RFC 00/11] DAX fsynx/msync support

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Date:	Thu, 29 Oct 2015 16:49:53 -0600
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Dave Chinner <david@...morbit.com>
Cc:	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Theodore Ts'o <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Chinner <david@...morbit.com>,
	Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-nvdimm@...ts.01.org, x86@...nel.org,
	xfs@....sgi.com, Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>
Subject: Re: [RFC 00/11] DAX fsynx/msync support

On Thu, Oct 29, 2015 at 02:12:04PM -0600, Ross Zwisler wrote:
> This patch series adds support for fsync/msync to DAX.
> 
> Patches 1 through 8 add various utilities that the DAX code will eventually
> need, and the DAX code itself is added by patch 9.  Patches 10 and 11 are
> filesystem changes that are needed after the DAX code is added, but these
> patches may change slightly as the filesystem fault handling for DAX is
> being modified ([1] and [2]).
> 
> I've marked this series as RFC because I'm still testing, but I wanted to
> get this out there so people would see the direction I was going and
> hopefully comment on any big red flags sooner rather than later.
> 
> I realize that we are getting pretty dang close to the v4.4 merge window,
> but I think that if we can get this reviewed and working it's a much better
> solution than the "big hammer" approach that blindly flushes entire PMEM
> namespaces [3].
> 
> [1] http://oss.sgi.com/archives/xfs/2015-10/msg00523.html
> [2] http://marc.info/?l=linux-ext4&m=144550211312472&w=2
> [3] https://lists.01.org/pipermail/linux-nvdimm/2015-October/002614.html

Hmm...I think I may need to isolate the fsync/msync flushing against races
with truncate since we are calling into the filesystem directly with
get_block().  Dave (Chinner), does this sound right?

Also, one thing I forgot to mention is that these patches are built upon the
first version of Dave Chinner's XFS patches and my ext2 patches that deal with
the truncate races with DAX.  A snapshot of my development tree with these
patches applied can be found here:

https://github.com/01org/prd/tree/fsync_rfc
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