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

[Ross Zwisler]

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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