From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 78FEC6B01EE for ; Mon, 5 Apr 2010 20:30:52 -0400 (EDT) Date: Mon, 5 Apr 2010 17:26:15 -0700 (PDT) From: Linus Torvalds Subject: Re: [PATCH 00 of 41] Transparent Hugepage Support #17 In-Reply-To: <20100405232115.GM5825@random.random> Message-ID: References: <20100405120906.0abe8e58.akpm@linux-foundation.org> <20100405193616.GA5125@elte.hu> <20100405232115.GM5825@random.random> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli Cc: Pekka Enberg , Ingo Molnar , Andrew Morton , linux-mm@kvack.org, Marcelo Tosatti , Adam Litke , Avi Kivity , Izik Eidus , Hugh Dickins , Nick Piggin , Rik van Riel , Mel Gorman , Dave Hansen , Benjamin Herrenschmidt , Mike Travis , KAMEZAWA Hiroyuki , Christoph Lameter , Chris Wright , bpicco@redhat.com, KOSAKI Motohiro , Balbir Singh , Arnd Bergmann , "Michael S. Tsirkin" , Peter Zijlstra , Johannes Weiner , Daisuke Nishimura List-ID: On Tue, 6 Apr 2010, Andrea Arcangeli wrote: > > Some performance result: Quite frankly, these "performance results" seem to be basically dishonest. Judging by your numbers, the big win is apparently pre-populating the page tables, the "tlb miss" you quote seem to be almost in the noise. IOW, we have memset page fault 1566023 vs memset page fault 2182476 looking like a major performance advantage, but then the actual usage is much less noticeable. IOW, how much of the performance advantage would we get from a _much_ simpler patch to just much more aggressively pre-populate the page tables (especially for just anonymous pages, I assume) or even just fault pages in several at a time when you have lots of memory? In particular, when you quote 6% improvement for a kernel compile, your own numbers make seriously wonder how many percentage points you'd get from just faulting in 8 pages at a time when you have lots of memory free, and use a single 3-order allocation to get those eight pages? Would that already shrink the difference between those "memset page faults" by a factor of eight? See what I'm saying? 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: email@kvack.org