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Date: Thu, 5 Apr 2018 08:10:38 -0700
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] dax: adding fsync/msync support for device DAX
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To: Jeff Moyer <jmoyer@redhat.com>
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On Thu, Apr 05, 2018 at 10:59:10AM -0400, Jeff Moyer wrote:
> So, I also hate this (note that this is already in place today for fs
> dax).  You have an operation to make things persistent, and another one
> to *really* make things persistent.  It makes no sense to me.  I have no
> idea how to communicate that to application developers.  When do you
> force things out to the smallest failure domain?
> 
> The arguments I've heard are that ADR failures may happen due to a
> variety of factors, and that an application (or file system) can make
> sure that critical (meta)data is available after a crash by flushing to
> the smallest failure domain.  Presumably, this would be a
> lower-frequency event (only for metadata changes, etc).

Which meansit should not abuse fsync but have a special interface
just for that IFF we trust ADR.  IFF we don't trust it anyway fsync
absolutely is the right interface, but then we shouldn't offer MAP_SYNC.
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