Re: [PATCH] move the kernel to 16MB for NUMA-Q

From: Rene Herman
Date: Mon Jun 11 2007 - 13:53:30 EST

On 06/11/2007 07:20 PM, Dave Jones wrote:

FWIW, waay back when (sometime last year if memory serves)
Linus suggested changing the default to 0x1000000 for all x86.
The reasoning was some performance microoptimisation regarding
4MB aligned TLBs iirc.

Yup. Or rather, he suggested 4M (0x400000):

Aligning the kernel image on 4M could gain an additional TLB entry if the kernel image would fit in one (4M aligned) hugepage, but not in the 3M that's left after loading the kernel at 1M physical. And that stuff about the MTRRs...

That 0x1000000 (16M) is another potentially interesting value on machines with enough memory as it gets the kernel image out of the old ZONE_DMA.

The details have long since evaded my memory, but as an experiment,
I made the change to the Fedora kernel. FC5,FC6 and F7 have been
this way for a while now, with no obvious problems. Ditto RHEL5.
We did get some performance numbers at the time of the change,
but they weren't amazing (basically in the noise).
Given it never seemed to actually get worse, I never got around
to reverting it..

I've been loading the kernel at 16M physical for ages now on x86. No problems either.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at