linux-kernel - Using pmem from a driver exposing a memory mapping (mmap) to userspace

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Date:	Tue, 28 Apr 2015 15:35:26 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Matthew Wilcox <willy@...ux.intel.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Boaz Harrosh <boaz@...xistor.com>,
	Christoph Hellwig <hch@....de>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Using pmem from a driver exposing a memory mapping (mmap) to
 userspace

Hi!

I'm currently adaping lttng-modules to use DAX and pmem.
It will allow LTTng buffers to be recovered after a kernel
crash. I've moved pretty much all struct page pointers to
page frame numbers, as I remember being told that pmem does
not have struct page.

Now I'm looking into adapting my mmap and page fault handler
implementation (based on struct page) to a page-frame number
based implementation when the ring buffer is backed by
persistent memory, which will probably not require any page
fault handler at all when based by pmem+dax memory.

My current work is in this branch: https://github.com/compudj/lttng-modules-dev/tree/persistent-memory-buffers
(see last commits)

LTTng-modules supports both mmap() and splice(), but I plan
to only provide mmap() support for persistent memory, since
splice() really requires struct page.

Are there existing driver mmap implementations doing similar
things, or do you have recommendations on how to implement
this ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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