From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 3 Nov 2005 08:46:12 -0800 (PST) From: Linus Torvalds Subject: Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19 In-Reply-To: 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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Mel Gorman Cc: Arjan van de Ven , "Martin J. Bligh" , 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, Mel Gorman wrote: > On Thu, 3 Nov 2005, Linus Torvalds wrote: > > > This is why fragmentation avoidance has always been totally useless. It is > > - only useful for big areas > > - very hard for big areas > > > > (Corollary: when it's easy and possible, it's not useful). > > > > Unless you are a user that wants a large area when it suddenly is useful. No. It's _not_ suddenly useful. It might be something you _want_, but that's a totally different issue. My point is that regardless of what you _want_, defragmentation is _useless_. It's useless simply because for big areas it is so expensive as to be impractical. Put another way: you may _want_ the moon to be made of cheese, but a moon made out of cheese is _useless_ because it is impractical. The only way to support big areas is to have special zones for them. (Then, we may be able to use the special zones for small things too, but under special rules, like "only used for anonymous mappings" where we can just always remove them by paging them out. But it would still be a special area meant for big pages, just temporarily "on loan"). 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