From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 2 Nov 2005 13:00:48 +0100 From: Ingo Molnar Subject: Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19 Message-ID: <20051102120048.GA10081@elte.hu> References: <20051102104131.GA7780@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Gerrit Huizenga Cc: Kamezawa Hiroyuki , Dave Hansen , Mel Gorman , Nick Piggin , "Martin J. Bligh" , Andrew Morton , kravetz@us.ibm.com, linux-mm , Linux Kernel Mailing List , lhms List-ID: * Gerrit Huizenga wrote: > > On Wed, 02 Nov 2005 11:41:31 +0100, Ingo Molnar wrote: > > > > * Gerrit Huizenga wrote: > > > > > > generic unpluggable kernel RAM _will not work_. > > > > > > Actually, it will. Well, depending on terminology. > > > > 'generic unpluggable kernel RAM' means what it says: any RAM seen by the > > kernel can be unplugged, always. (as long as the unplug request is > > reasonable and there is enough free space to migrate in-use pages to). > > Okay, I understand your terminology. Yes, I can not point to any > particular piece of memory and say "I want *that* one" and have that > request succeed. However, I can say "find me 50 chunks of memory > of your choosing" and have a very good chance of finding enough > memory to satisfy my request. but that's obviously not 'generic unpluggable kernel RAM'. It's very special RAM: RAM that is free or easily freeable. I never argued that such RAM is not returnable to the hypervisor. > > reliable unmapping of "generic kernel RAM" is not possible even in a > > virtualized environment. Think of the 'live pointers' problem i outlined > > in an earlier mail in this thread today. > > Yeah - and that isn't what is being proposed here. The goal is to > ask the kernel to identify some memory which can be legitimately > freed and hasten the freeing of that memory. but that's very easy to identify: check the free list or the clean list(s). No defragmentation necessary. [unless the unit of RAM mapping between hypervisor and guest is too coarse (i.e. not 4K pages).] Ingo -- 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