linux-ext4 - Re: [PATCH v2 00/11] DAX fsynx/msync support

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Date:	Mon, 16 Nov 2015 15:41:30 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.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>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v2 00/11] DAX fsynx/msync support

On Fri 13-11-15 17:06:39, Ross Zwisler wrote:
> This patch series adds support for fsync/msync to DAX.
> 
> Patches 1 through 7 add various utilities that the DAX code will eventually
> need, and the DAX code itself is added by patch 8.  Patches 9-11 update the
> three filesystems that currently support DAX, ext2, ext4 and XFS, to use
> the new DAX fsync/msync code.
> 
> These patches build on the recent DAX locking changes from Dave Chinner,
> Jan Kara and myself.  Dave's changes for XFS and my changes for ext2 have
> been merged in the v4.4 window, but Jan's are still unmerged.  You can grab
> them here:
> 
> http://www.spinics.net/lists/linux-ext4/msg49951.html

I had a quick look and the patches look sane to me. I'll try to give them
more detailed look later this week. When thinking about the general design
I was wondering: When we have this infrastructure to track data potentially
lingering in CPU caches, would not it be a performance win to use standard
cached stores in dax_io() and mark corresponding pages as dirty in page
cache the same way as this patch set does it for mmaped writes? I have no
idea how costly are non-temporal stores compared to cached ones and how
would this compare to the cost of dirty tracking so this may be just
completely bogus...

								Honza

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