Re: Machine's high load when HIGHMEM is enabled

vasya vasyaev
2002-11-04T18:48:09Z

Hello,

First of all - thanks to these people, who responded
to my question.

I have some news...

I've tried kernels:
2.4.19 - the same result
2.5.44 - the same result
2.5.45 - the same result

If I take 1 Gb of memory away, then computer works
much better, faster (something like without enabled
HIGHMEM at all).
The same effect takes place if I say mem=1024M while
physically box has 2Gb of RAM - everything is fine!
But if I start HIGHMEM enabled kernel on this box (2Gb
RAM), then it works too slowly...

The questions are:
1. is there anyone on the list, who has the same or
near configuration ? (main is that the box has >=2Gb
of RAM)
2. do you experience the same problems ?
3. maybe it's not a problem at all?!? I mean maybe
linux kernel works this way with such amount of memory
and there is no problem with that?
4. the case I've described =
http://www.cs.helsinki.fi/linux/linux-kernel/2001-02/0292.html
?

and finally, if this could be solved - please tell,
how should I set up the kernel/kernel settings to get
appropriate results in performance ?

Thank you.

--- Brian Gerst <bgerst@quark.didntduck.org> wrote:
> 2.4 can only do I/O to and from lowmem. This means
> highmem pages have
> to use bounce buffers in lowmem, and th edata is
> copied to/from highmem
> which is causing the cpu load. This has been
> corrected in 2.5, which
> can do I/O to any page the device can DMA from.

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