From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx164.postini.com [74.125.245.164]) by kanga.kvack.org (Postfix) with SMTP id 4B2A76B0062 for ; Tue, 30 Oct 2012 18:31:59 -0400 (EDT) Date: Tue, 30 Oct 2012 15:31:57 -0700 From: Andrew Morton Subject: Re: [PATCH v2] mm: memmap_init_zone() performance improvement Message-Id: <20121030153157.70279408.akpm@linux-foundation.org> In-Reply-To: <1351291667.6504.13.camel@MikesLinux.fc.hp.com> References: <1349276174-8398-1-git-send-email-mike.yoknis@hp.com> <20121008151656.GM29125@suse.de> <1349794597.29752.10.camel@MikesLinux.fc.hp.com> <1350676398.1169.6.camel@MikesLinux.fc.hp.com> <20121020082858.GA2698@suse.de> <1351093667.1205.11.camel@MikesLinux.fc.hp.com> <20121025094410.GA2558@suse.de> <1351291667.6504.13.camel@MikesLinux.fc.hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: mike.yoknis@hp.com Cc: Mel Gorman , mingo@redhat.com, linux-arch@vger.kernel.org, mmarek@suse.cz, tglx@linutronix.de, hpa@zytor.com, arnd@arndb.de, sam@ravnborg.org, minchan@kernel.org, kamezawa.hiroyu@jp.fujitsu.com, mhocko@suse.cz, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Fri, 26 Oct 2012 16:47:47 -0600 Mike Yoknis wrote: > memmap_init_zone() loops through every Page Frame Number (pfn), > including pfn values that are within the gaps between existing > memory sections. The unneeded looping will become a boot > performance issue when machines configure larger memory ranges > that will contain larger and more numerous gaps. > > The code will skip across invalid pfn values to reduce the > number of loops executed. > So I was wondering how much difference this makes. Then I see Mel already asked and was answered. The lesson: please treat a reviewer question as a sign that the changelog needs more information! I added this text to the changelog: : We have what we call an "architectural simulator". It is a computer : program that pretends that it is a computer system. We use it to test the : firmware before real hardware is available. We have booted Linux on our : simulator. As you would expect it takes longer to boot on the simulator : than it does on real hardware. : : With my patch - boot time 41 minutes : Without patch - boot time 94 minutes : : These numbers do not scale linearly to real hardware. But indicate to me : a place where Linux can be improved. > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3857,8 +3857,11 @@ void __meminit memmap_init_zone(unsigned long > size, int nid, unsigned long zone, > * exist on hotplugged memory. > */ > if (context == MEMMAP_EARLY) { > - if (!early_pfn_valid(pfn)) > + if (!early_pfn_valid(pfn)) { > + pfn = ALIGN(pfn + MAX_ORDER_NR_PAGES, > + MAX_ORDER_NR_PAGES) - 1; > continue; > + } > if (!early_pfn_in_nid(pfn, nid)) > continue; > } So what is the assumption here? That each zone's first page has a pfn which is a multiple of MAX_ORDER_NR_PAGES? That seems reasonable, but is it actually true, for all architectures and for all time? Where did this come from? -- 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