From: Andi Kleen <andi@firstfloor.org>
To: Fabio De Francesco <fabiomdf@alice.it>
Cc: Arjan van de Ven <arjan@infradead.org>,
linux-kernel@vger.kernel.org, Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [x86_32] With 4GB installed, in which cases low mem total is less than 896MB?
Date: Fri, 02 May 2008 17:47:17 +0200 [thread overview]
Message-ID: <87skx0vhbu.fsf@basil.nowhere.org> (raw)
In-Reply-To: <200805021638.52540.fabiomdf@alice.it> (Fabio De Francesco's message of "Fri, 2 May 2008 16:38:46 +0200")
Fabio De Francesco <fabiomdf@alice.it> writes:
>
> Unfortunetally my poor knowledge of Linux kernel mechanisms (and
> code!) prevents me from understanding what could be the causes for
> that overhead. Do you mean it is a hardware issue? Or is it a kernel
> one? Anyway another machine of mine, that is equipped with 2GB RAM,
> doesn't show any proportional reduction of low memory at all. So
> this makes me think (oh, dear!).
You might want to read http://halobates.de/memorywaste.pdf, in
particular 3.5.2. The numbers arjan quoted and in the paper
are for 64bit kernels, on 32bit the overhead is ~32bytes/page. This
mem_map overhead happens for both highmem and lowmem, but is always
allocated in lowmem.
-Andi
next prev parent reply other threads:[~2008-05-02 15:47 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-30 15:02 [x86_32] With 4GB installed, in which cases low mem total is less than 896MB? Fabio De Francesco
2008-04-29 17:18 ` Arjan van de Ven
2008-05-02 14:38 ` Fabio De Francesco
2008-05-02 15:47 ` Andi Kleen [this message]
2008-04-30 16:55 ` Alan Cox
2008-05-04 14:37 ` Rene Herman
2008-05-08 7:48 ` Fabio De Francesco
2008-05-08 12:35 ` Rene Herman
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