linux-kernel - Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?")

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Message-ID: <20090806201527.GA8725@shareable.org>
Date:	Thu, 6 Aug 2009 21:15:27 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	David Xiao <dxiao@...adcom.com>
Cc:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Ben Dooks <ben-linux@...ff.org>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Robin Holt <holt@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	v4l2_linux <linux-media@...r.kernel.org>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>
Subject: Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?")

David Xiao wrote:
> Another approach is working from a different direction: the kernel
> allocates the non-cached buffer and then mmap() into user space. I have
> done that in similar situation to try to achieve "zero-copy". 

open(O_DIRECT) does DMA to arbitrary pages allocated by userspace, and
O_DIRECT is used by some important applications, so the problem still
needs to be solved in general.

-- Jamie
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