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Subject: Re: [Lsf-pc] [LSF/MM TOPIC] The end of the DAX experiment
To:     Dan Williams <dan.j.williams@intel.com>,
        Michal Hocko <mhocko@kernel.org>
Cc:     lsf-pc@lists.linux-foundation.org,
        linux-xfs <linux-xfs@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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From:   Boaz Harrosh <openosd@gmail.com>
Message-ID: <5a45a763-d060-7cb1-9772-dd6e9f5f868a@gmail.com>
Date:   Mon, 9 Dec 2019 18:20:24 +0200
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On 14/02/2019 20:25, Dan Williams wrote:
> On Thu, Feb 14, 2019 at 5:46 AM Michal Hocko <mhocko@kernel.org> wrote:
>>
>> On Wed 06-02-19 13:12:59, Dan Williams wrote:
>> [...]
>>> * Userfaultfd for file-backed mappings and DAX
>>
>> I assume that other topics are meant to be FS track but this one is MM,
>> right?
> 
> Yes, but I think it is the lowest priority of all the noted sub-topics
> in this proposal. The DAX-reflink discussion, where a given
> physical-page may need to be mapped into multiple inodes at different
> offsets, might be more fruitful to have as a joint discussion with MM.
> 

This topic is very interesting to me.
In current ZUFS implementation we support this option for a long time.

IE: Map same pte_t into different indexes of the same file-mappings as well as
in vma(s) of different files, at different indexes. Including invalidation
of mapping of a pwrite into such a shared page.
(A write to a shared block will allocate a new block for writing)

This effort off-course involves the participation of the FileSystem
to give a list of files and indexes for map_unmapping().
I can explain if you want how we did this.

Cheers
Boaz