[Gllug] Wrong "mem=XXXm" makes kernel *slow*?

[Mike Brodbelt]

On Mon, 2005-02-21 at 21:35 +0000, John Winters wrote:

> Reducing the memory further (to 992m - i.e. 32m reserved) got the system
> to boot normally.  Now, I can understand why not reserving enough causes
> the system to crash, but I can't imagine why it would cause the system
> to run very slowly.  Anyone know why?

Typically this happens because the motherboard chipset doesn't properly
cache all the installable memory on the board. Ther kernel loads at the
top of memory, so if that area is in uncached memory it slows everything
down straight away. The slram kernel driver is provided to allow the use
of this memory as fast disk, though in 2.6 I think the suggestion is to
use phram (which I've never looked at). Of course motherboard docs
rarely make a point of mentioning that only 1/2 or 2/3 of the max
installable memory is actually handled by the chipset....

HTH,

Mike.

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