Re: Increase page fault rate by prezeroing V1 [1/3]: Introduce__GFP_ZERO

From: Christoph Lameter
Date: Wed Dec 22 2004 - 14:56:21 EST

On Wed, 22 Dec 2004, Andi Kleen wrote:

> It depends. If you plan to do really big zero_page then it
> may be worth experimenting with cache bypassing clears
> (movntq) or even SSE2 16 byte stores (movntdq %xmm..,..)
> and take out the rep ; stosq optimization. I tried it all
> long ago and it wasn't a win for only 4K.
> For normal 4K clear_page that's definitely not a win (tested)
> and especially cache bypassing is a loss.

This may be better realized using a zeroing driver then.

> Yours too at least on non Altix no? Can you demonstrate any benefit?
> Where are the numbers?

In the initial discussion see V1 [0/3].

> I'm sceptical for example that there will be enough higher orders
> to make the batch clearing worthwhile after the system is up for a days.
> Normally memory tends to fragment rather badly in Linux.
> I suspect after some time your approach will just degenerate to be
> the same as Andrea's, even if it should be a win at the beginning (is it?)

I have tried it and the number show clearly that this continues to be a
win although the inital 7-8 fold speed increase degenerates into 3-4 fold
over time (single thread performance).
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