Re: -mmX 4G patches feedback [numbers: how much performance impact]

[Martin J. Bligh]

--On Thursday, April 08, 2004 01:18:06 +0200 Andrea Arcangeli <andrea@xxxxxxx> wrote:

> On Wed, Apr 07, 2004 at 04:21:44PM -0700, Martin J. Bligh wrote:
>> Speaking of which, pte_highmem is stinking expensive itself. There's
>> probably a large class of workloads that'd work with out pte_highmem
>> if we had 4/4 split (or shared pagetables. Grrr ;-))
> 
> hey, I can add a sysctl in 5 minutes to disable pte_highmem at runtime,
> why do you think it's expensive, it should be not, it's all atomic kmaps
> only doing invlpg. The few workloads trashing on the ptes manipulation
> needs pte_highmem anyways. If I thought it was expensive for any common
> load the sysctl would be already there.

I measured it - IIRC it was 5-10% on kernel compile ... and that was on a
high ratio NUMA which it should have made *better* (as with highmem, the
PTEs can be allocated node locally). I'll try to dig up the old profiles.

M.

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