Re: [PATCH 5/5] block: enable dax for raw block devices

[Dave Chinner]

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@xxxxxxxxxxxxx
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