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Date:   Wed, 21 Sep 2022 17:15:52 -0700
From:   Dan Williams <dan.j.williams@intel.com>
To:     Jason Gunthorpe <jgg@nvidia.com>,
        Dan Williams <dan.j.williams@intel.com>
CC:     <akpm@linux-foundation.org>, Matthew Wilcox <willy@infradead.org>,
        "Jan Kara" <jack@suse.cz>, "Darrick J. Wong" <djwong@kernel.org>,
        "Christoph Hellwig" <hch@lst.de>,
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        <linux-xfs@vger.kernel.org>, <linux-mm@kvack.org>,
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Subject: Re: [PATCH v2 15/18] devdax: Use dax_insert_entry() +
 dax_delete_mapping_entry()
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Jason Gunthorpe wrote:
> On Wed, Sep 21, 2022 at 08:48:22AM -0700, Dan Williams wrote:
> 
> > The fsdax core now manages pgmap references when servicing faults that
> > install new mappings, and elevates the page reference until it is
> > zapped. It coordinates with the VFS to make sure that all page
> > references are dropped before the hosting inode goes out of scope
> > (iput_final()).
> >
> > In order to delete the unnecessary pgmap reference taking in mm/gup.c
> > devdax needs to move to the same model.
> 
> I think this patch is more about making devdax and fsdax use the same
> set of functions and logic so that when it gets to patch 16/17 devdax
> doesn't break. That understanding matches the first paragraph, at
> least.
> 
> I would delete the remark about gup since it is really patch 17 that
> allows gup to be fixed by making it so that refcount == 0 means not to
> look at the pgmap (instead of refcount == 1 as is now) ?

Yeah, makes sense.