Re: [PATCH] Prezeroing V8

[Christoph Lameter]

On Thu, 17 Mar 2005, Andrew Morton wrote:

> >  http://oss.sgi.com/projects/page_fault_performance/
>
> Oh no, not that page again ;)

Yes indeed!

> Seems to say that prezeroing makes negligible difference to kernel builds,
> but speeds up a big malloc+memset by 3x to 4x, yes?

Correct.

> Are there any real-worldish workloads which show an appreciable benefit?

Ummm. Big loads are our real-worldish workloads here.

> The large speedup for a big memset seems odd - I assume it's simply
> transferring CPU load from the user's process over to kscrubd.  Or is it
> the fancy page-zeroing hardware?  How do we differentiate the two?

I switched off the page-zeroing hardware for the tests.

> Are there any workloads which are seeing a benefit on a CPU which doesn't
> have the zeroing hardware?

Without zeroing hardware the eroing actions are moved to idle
system time (load < /proc/sys/vm/scrub_load). Its shifting the cpu load.

But I just fixed things up so that the kernel can return hot zeroed
pages to the pool for quicklist management. This yields zeroed pages
without kscrubd.
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