linux-kernel - Re: Question about memory mapping mechanism

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Message-ID: <Pine.LNX.4.64.0703090227490.27568@kepler.fjfi.cvut.cz>
Date:	Fri, 9 Mar 2007 02:31:54 +0100 (CET)
From:	Martin Drab <drab@...ler.fjfi.cvut.cz>
To:	Carsten Otte <cotte.de@...il.com>
cc:	hugh@...itas.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Question about memory mapping mechanism

On Fri, 9 Mar 2007, Martin Drab wrote:

> On Thu, 8 Mar 2007, Martin Drab wrote:
> 
> > On Thu, 8 Mar 2007, Carsten Otte wrote:
> > 
> > > 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.
> > 
> > I'm not really sure what exactly do you mean by "grab a reference 
> > upfront"?
> 
> I seem to get it now. So instead of setting PG_reserved upon allocation of 
> the buffer pages, I should increase the referrence of the pages by calling 
> get_page() on them and that would prevent the pages to get on the lru list 
> and thus preventing them to be swapped out. Is that it?

Well, so I tried it. Truth is that the "Bad page" messages upon munmap(2) 
are gone. But whether the pages are really prevented from being swapped 
out? I don't know. I don't know how to find out.

Martin
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