Date: Wed, 26 Aug 2015 14:46:49 +0200
From: Christoph Hellwig <hch@lst.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm@ml01.01.org, boaz@plexistor.com, david@fromorbit.com,
        linux-kernel@vger.kernel.org, hch@lst.de, linux-mm@kvack.org,
        hpa@zytor.com, ross.zwisler@linux.intel.com, mingo@kernel.org
Subject: Re: [PATCH v2 9/9] devm_memremap_pages: protect against pmem
	device unbind
Message-ID: <20150826124649.GA8014@lst.de>
References: <20150826010220.8851.18077.stgit@dwillia2-desk3.amr.corp.intel.com> <20150826012813.8851.35482.stgit@dwillia2-desk3.amr.corp.intel.com>
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On Tue, Aug 25, 2015 at 09:28:13PM -0400, Dan Williams wrote:
> 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.

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