Re: [PATCH v3 02/13] dax: require 'struct page' for filesystem dax

[Christoph Hellwig]

On Fri, Oct 20, 2017 at 08:23:02AM -0700, Dan Williams wrote:
> Yes, however it seems these drivers / platforms have been living with
> the lack of struct page for a long time. So they either don't use DAX,
> or they have a constrained use case that never triggers
> get_user_pages(). If it is the latter then they could introduce a new
> configuration option that bypasses the pfn_t_devmap() check in
> bdev_dax_supported() and fix up the get_user_pages() paths to fail.
> So, I'd like to understand how these drivers have been using DAX
> support without struct page to see if we need a workaround or we can
> go ahead delete this support. If the usage is limited to
> execute-in-place perhaps we can do a constrained ->direct_access() for
> just that case.

For axonram I doubt anyone is using it any more - it was a very for
the IBM Cell blades, which were produceÑ in a rather limited number.
And Cell basically seems to be dead as far as I can tell.

For S/390 Martin might be able to help out what the status of xpram
in general and DAX support in particular is.