linux-kernel - Re: [PATCH v2 9/9] devm_memremap_pages: protect against pmem device unbind

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Message-ID: <20150826124649.GA8014@lst.de>
Date:	Wed, 26 Aug 2015 14:46:49 +0200
From:	Christoph Hellwig <hch@....de>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-nvdimm@...ts.01.org, boaz@...xistor.com, david@...morbit.com,
	linux-kernel@...r.kernel.org, hch@....de, linux-mm@...ck.org,
	hpa@...or.com, ross.zwisler@...ux.intel.com, mingo@...nel.org
Subject: Re: [PATCH v2 9/9] devm_memremap_pages: protect against pmem
	device unbind

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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