From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 6 Sep 2008 18:17:40 +0200 From: Ingo Molnar Subject: Re: Re: [PATCH] [RESEND] x86_64: add memory hotremove config option Message-ID: <20080906161740.GB10238@elte.hu> References: <20080906143318.GA23621@elte.hu> <20080905215452.GF11692@us.ibm.com> <20080906000154.GC18288@one.firstfloor.org> <20080906153855.7260.E1E9C6FF@jp.fujitsu.com> <9031244.1220716855172.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9031244.1220716855172.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org Return-Path: To: kamezawa.hiroyu@jp.fujitsu.com Cc: Yasunori Goto , Andi Kleen , Gary Hade , linux-mm@kvack.org, Andrew Morton , Badari Pulavarty , Mel Gorman , Chris McDermott , linux-kernel@vger.kernel.org, x86@kernel.org List-ID: * kamezawa.hiroyu@jp.fujitsu.com wrote: > > Removing those limitations of kernel-space allocations should indeed > > be done in baby steps - and whether it's worth turning such memory > > into completely generic kernel memory is an open question. > > I think generic kernel space memory hotplug will never be available. yeah, most likely. (It's possible technically even on a native kernel - just very expensive to various aspects of the kernel.) > > But the fact that a piece of memory is not fully generic is no > > reason not to allow users to create special, capability-limited RAM > > resources like they can already do via hugetlbfs or ramfs, as long > > as the the capability limitations are advertised clearly. > > Hmm, adding a feature like > - offline some memory at boot. > - online-memory-as-hugeltb mode > > is useful for generic pc users ? yeah - it's actually the way how hugetlb should be done. Plus expand gbpages to hugetlbfs and hotplug memory on Barcelona CPUs and you can do user-space apps that can run for a long time without any TLB misses. _That_ might make sense to explore in practice. (i'm not holding my breath though, TLB misses are _fast_ on the best x86 CPUs.) But we wont be able to make such experiments without having the capability on x86. So i'd like to break the catch-22 by accepting all this into arch/x86, it certainly is simple and makes some sense, it's just that i'm not that convinced about it personally at the moment. So feel free to turn it all into a killer feature (make hugetlb backed memory transparent to user-space, etc. etc.) that high-performance computing users strive for and all that will change. Please send the reshaped patches so we can move past the 'what if' discussion phase ;-) 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