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From: Jeff Moyer <jmoyer@redhat.com>
Subject: Re: Snapshot target and DAX-capable devices
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Date: Thu, 30 Aug 2018 15:53:31 -0400
In-Reply-To: <alpine.LRH.2.02.1808301545200.30950@file01.intranet.prod.int.rdu2.redhat.com>
 (Mikulas Patocka's message of "Thu, 30 Aug 2018 15:47:32 -0400 (EDT)")
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To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Jan Kara <jack@suse.cz>, Mike Snitzer <snitzer@redhat.com>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>, "dm-devel@redhat.com" <dm-devel@redhat.com>, "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
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Mikulas Patocka <mpatocka@redhat.com> writes:

> On Thu, 30 Aug 2018, Jeff Moyer wrote:
>
>> Mike Snitzer <snitzer@redhat.com> writes:
>> 
>> > Until we properly add DAX support to dm-snapshot I'm afraid we really do
>> > need to tolerate this "regression".  Since reality is the original
>> > support for snapshot of a DAX DM device never worked in a robust way.
>> 
>> Agreed.
>> 
>> -Jeff
>
> You can't support dax on snapshot - if someone maps a block and the block 
> needs to be moved, then what?

That's exactly the point I brought up in my reply to Jan.  You'd have to
unmap all mappings of the page/block.

-Jeff
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