Messages in this thread | | | Date | Fri, 07 Dec 2001 17:52:48 -0800 | From | "H. Peter Anvin" <> | Subject | Re: highmem question |
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Marvin Justice wrote:
>>The problem is that in the x86 architecture you don't have any reasonable >>way of addressing the physical address space, so you need to map it into >>the virtual address space. You end up with a shortage of virtual address >>space. >> > > Isn't this still just an artifact of the default 1:3 kernel/user virtual > address space split? I've never tried it myself but isn't there a 2:2 patch > available that has the effect of moving the highmem boundary up? >
You can tweak the split... both 2:2 and 0.5:3.5 splits have been used... but it's not without side effects. Cutting your user space breaks applications which want large mmap() areas, for example.
> >>There is no way of fixing it. >> > > All I know is that a streaming io app I was playing with showed a drastic > performance hit when the kernel was compiled with CONFIG_HIGHMEM. On W2K we > saw no slowdown with 2 or even 4GB of RAM so I think solutions must exist. >
Of course you didn't. Win2K runs with the equivalent of HIGHMEM all the time.
-hpa
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