linux-kernel - Re: [PATCH 2/2] cuse: implement memory mapping

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Message-ID: <CA+55aFy7xLkMThg8+G=e7v7x7WaHSkLWGRiRF8hCq4WEUHxymw@mail.gmail.com>
Date:	Fri, 13 Jan 2012 10:19:50 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org, htejun@...il.com,
	david.henningsson@...onical.com, smcnam@...il.com,
	gmane@...in.guthr.ie, jamescaldwell1@...il.com,
	s.maddox@...tizia.me.uk, mszeredi@...e.cz
Subject: Re: [PATCH 2/2] cuse: implement memory mapping

On Fri, Jan 13, 2012 at 9:06 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
> From: Tejun Heo <htejun@...il.com>
>
> This implements memory mapping of char devices.

I don't think this is how you want to do it.

It seems to maintain a page list of its own, and do the magic page
fault etc behavior. Which to me smells like a really bad design.

I would expect that what you actually want to do is to expose it as a
shared mmap, and depend on all the normal shmem support. Is there any
reason not to do that?

I guess you don't generally have big mappings, so an argument like
"that way you can page out pages etc" may not strike you as a very
strong argument, but I'd still prefer to at least see that approach
explored. Hmm?

                     Linus
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