From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 3 Nov 2005 10:08:23 -0800 (PST) From: Linus Torvalds Subject: Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19 In-Reply-To: <1131040786.2839.18.camel@laptopd505.fenrus.org> Message-ID: References: <4366C559.5090504@yahoo.com.au> <4366D469.2010202@yahoo.com.au> <20051101135651.GA8502@elte.hu> <1130854224.14475.60.camel@localhost><20051101142959.GA9272@elte.hu> <1130856555.14475.77.camel@localhost><20051101150142.GA10636@elte.hu> <1130858580.14475.98.camel@localhost><20051102084946.GA3930@elte.hu> <436880B8.1050207@yahoo.com.au><1130923969.15627.11.camel@localhost> <43688B74.20002@yahoo.com.au><255360000.1130943722@[10.10.2.4]> <4369824E.2020407@yahoo.com.au> <306020000.1131032193@[10.10.2.4]> <1131032422.2839.8.camel@laptopd505.fenrus.org> <309420000.1131036740@[10.10.2.4]> <311050000.1131040276@[10.10.2.4]> <1131040786.2839.18.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: "Martin J. Bligh" , Mel Gorman , Nick Piggin , Dave Hansen , Ingo Molnar , Andrew Morton , kravetz@us.ibm.com, linux-mm , Linux Kernel Mailing List , lhms , Arjan van de Ven List-ID: On Thu, 3 Nov 2005, Arjan van de Ven wrote: > On Thu, 2005-11-03 at 09:51 -0800, Martin J. Bligh wrote: > > > For amusement, let me put in some tritely oversimplified math. For the > > sake of arguement, assume the free watermarks are 8MB or so. Let's assume > > a clean 64-bit system with no zone issues, etc (ie all one zone). 4K pages. > > I'm going to assume random distribution of free pages, which is > > oversimplified, but I'm trying to demonstrate a general premise, not get > > accurate numbers. > > that is VERY over simplified though, given the anti-fragmentation > property of buddy algorithm Indeed. I write a program at one time doing random allocation and de-allocation and looking at what the output was, and buddy is very good at avoiding fragmentation. These days we have things like per-cpu lists in front of the buddy allocator that will make fragmentation somewhat higher, but it's still absolutely true that the page allocation layout is _not_ random. 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