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From: Jeff Moyer <jmoyer@redhat.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>, Jan Kara <jack@suse.cz>,
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Subject: Re: Snapshot target and DAX-capable devices
References: <20180827160744.GE4002@quack2.suse.cz>
        <e38303902267d2d8bae8b0c88da84a4ed668e9fb.camel@hpe.com>
        <20180828075025.GA17756@quack2.suse.cz>
        <20180828175630.GA1197@redhat.com>
        <20180830093028.GC1767@quack2.suse.cz>
        <20180830184907.GA14867@redhat.com>
        <x494lfbabwi.fsf@segfault.boston.devel.redhat.com>
        <alpine.LRH.2.02.1808301545200.30950@file01.intranet.prod.int.rdu2.redhat.com>
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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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