On Wed, Aug 26, 2015 at 09:39:18PM +0000, Williams, Dan J wrote:

On Wed, 2015-08-26 at 14:46 +0200, Christoph Hellwig wrote:

quoted

On Tue, Aug 25, 2015 at 09:28:13PM -0400, Dan Williams wrote:

quoted

Given that:

1/ device ->remove() can not be failed

2/ a pmem device may be unbound at any time

3/ we do not know what other parts of the kernel are actively using a
   'struct page' from devm_memremap_pages()

...provide a facility for active usages of device memory to block pmem
device unbind.  With a percpu_ref it should be feasible to take a
reference on a per-I/O or other high frequency basis.

Without a caller of get_page_map this is just adding dead code.  I'd
suggest to group it in a series with that caller.

Agreed, we can drop this until the first user arrives.

quoted

Also if the page_map gets exposed in a header the name is a bit too generic.
memremap_map maybe?

Done, and in the patch below I hide the internal implementation details
of page_map in kernel/memremap.c and only expose the percpu_ref in the
public memremap_map.

Yes, that looks good once we're getting the users for it.

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