From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 24 Dec 2004 10:21:24 -0800 (PST) From: Linus Torvalds Subject: Re: Prezeroing V2 [0/3]: Why and When it works In-Reply-To: <1103879668.4131.15.camel@laptopd505.fenrus.org> Message-ID: References: <41C20E3E.3070209@yahoo.com.au> <16843.13418.630413.64809@cargo.ozlabs.ibm.com> <1103879668.4131.15.camel@laptopd505.fenrus.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Arjan van de Ven Cc: Paul Mackerras , Christoph Lameter , Andrew Morton , linux-ia64@vger.kernel.org, linux-mm@kvack.org, Kernel Mailing List List-ID: On Fri, 24 Dec 2004, Arjan van de Ven wrote: > > problem is.. will it buy you anything if you use the page again > anyway... since such pages will be cold cached now. So for sure some of > it is only shifting latency from kernel side to userspace side, but > readprofile doesn't measure the later so it *looks* better... Absolutely. I would want to see some real benchmarks before we do this. Not just some microbenchmark of "how many page faults can we take without _using_ the page at all". I agree 100% with you that we shouldn't shift the costs around. Having a hice hot-spot that we know about is a good thing, and it means that performance profiles show what the time is really spent on. Often getting rid of the hotspot just smears out the work over a wider area, making other optimizations (like trying to make the memory footprint _smaller_ and removing the work entirely that way) totally impossible because now the performance profile just has a constant background noise and you can't tell what the real problem is. Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org