linux-kernel - Re: Question about memory mapping mechanism

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Message-ID: <5c77e7070703080620i3e2a3a64sf9d3121e4f6d382a@mail.gmail.com>
Date:	Thu, 8 Mar 2007 15:20:02 +0100
From:	"Carsten Otte" <cotte.de@...il.com>
To:	"Martin Drab" <drab@...ler.fjfi.cvut.cz>
Cc:	hugh@...itas.com,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: Question about memory mapping mechanism

On 3/8/07, Martin Drab <drab@...ler.fjfi.cvut.cz> wrote:
> The thing is that I'd like to prevent kernel to swap these pages out,
> because then I may loose some data when they are not available in time
> for the next round.

One think you could do is grab a reference to the pages upfront. When
you stop pushing data out to the userspace, or at least when the file
is released, you need to drop that reference again. You could even do
a kmap_atomic(), which would give you a kernel space mapping. That
way, you avoid copy_to_user for that data.
I am not sure if that's the "proper way", just my $0.02 how I would
try to solve it.

Carsten
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