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

From: H. Peter Anvin
Date: Mon Jun 11 2007 - 13:37:54 EST

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.
> 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..

Picking the 16 MB base is a bit obnoxious on small-memory machines, 4 MB
would probably be a more reasonable base. Of course, 16 MB would avoid
the issue of the handful of machines with memory holes at 15-16 MB.

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