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Date:	Mon, 26 Oct 2015 08:22:47 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>, "hch@....de" <hch@....de>,
	"axboe@...com" <axboe@...com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"willy@...ux.intel.com" <willy@...ux.intel.com>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH 5/5] block: enable dax for raw block devices

On Thu, Oct 22, 2015 at 11:08:18PM +0200, Jan Kara wrote:
> Ugh2: Now I realized that DAX mmap isn't safe wrt fs freezing even for
> filesystems since there's nothing which writeprotects pages that are
> writeably mapped. In normal path, page writeback does this but that doesn't
> happen for DAX. I remember we once talked about this but it got lost.
> We need something like walk all filesystem inodes during fs freeze and
> writeprotect all pages that are mapped. But that's going to be slow...

fsync() has the same problem - we have no record of the pages that
need to be committed and then write protected when fsync() is called
after write()...

Cheers,

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