[nylug-talk] LOWMEM vs. HIGHMEM performance advantage?

[Ajai Khattri]

On Thu, 17 Apr 2008, jh wrote:

> The reason why I ask: using this app with smaller jobs uses less memory, 
> and hence, I was wondering if the himem/lowmem split could explain 
> anything. Otherwise, it is likely a peculiarity of the app itself, and 
> the question is better directed to the developer.

Ah, I see what you mean. You might be right. Anything close to 1Gb or more 
involves an extra layer of page mapping from HIGHMEM into LOWMEM zones 
before the kernel can access it so yeah that might account for slower 
processing when running close to 1Gb.

(Actually, the normal mapping is more like 0 to 896Mb since the kernel 
grabs 128Mb for itself so you dont get the full 1Gb to play with in the 
norml zone).

Note: Im talking about the traditional 1Gb/3Gb split here - kernel patches 
exist to do 2Gb/2Gb split if you want.


-- 
Aj.