Messages in this thread | | | Date | Wed, 22 Dec 2004 11:54:09 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: Increase page fault rate by prezeroing V1 [1/3]: Introduce __GFP_ZERO |
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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). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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