Re: [Lsf-pc] [LSF/MM TOPIC] The end of the DAX experiment

From: Boaz Harrosh
Date: Mon Dec 09 2019 - 11:20:31 EST

On 14/02/2019 20:25, Dan Williams wrote:
> On Thu, Feb 14, 2019 at 5:46 AM Michal Hocko <mhocko@xxxxxxxxxx> 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.