From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f54.google.com (mail-pb0-f54.google.com [209.85.160.54]) by kanga.kvack.org (Postfix) with ESMTP id 4BB3F6B0031 for ; Wed, 9 Oct 2013 20:28:48 -0400 (EDT) Received: by mail-pb0-f54.google.com with SMTP id ro12so1705258pbb.13 for ; Wed, 09 Oct 2013 17:28:47 -0700 (PDT) Message-ID: <1381364704.5429.146.camel@misato.fc.hp.com> Subject: Re: [PATCH part1 v6 4/6] x86/mem-hotplug: Support initialize page tables in bottom-up From: Toshi Kani Date: Wed, 09 Oct 2013 18:25:04 -0600 In-Reply-To: <5255C730.90602@zytor.com> References: <524E2032.4020106@gmail.com> <524E2127.4090904@gmail.com> <5251F9AB.6000203@zytor.com> <525442A4.9060709@gmail.com> <20131009164449.GG22495@htj.dyndns.org> <52558EEF.4050009@gmail.com> <20131009192040.GA5592@mtj.dyndns.org> <1381352311.5429.115.camel@misato.fc.hp.com> <20131009211136.GH5592@mtj.dyndns.org> <5255C730.90602@zytor.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "H. Peter Anvin" Cc: Tejun Heo , Zhang Yanfei , Andrew Morton , "Rafael J . Wysocki" , lenb@kernel.org, Thomas Gleixner , mingo@elte.hu, Wanpeng Li , Thomas Renninger , Yinghai Lu , Jiang Liu , Wen Congyang , Lai Jiangshan , isimatu.yasuaki@jp.fujitsu.com, izumi.taku@jp.fujitsu.com, Mel Gorman , Minchan Kim , mina86@mina86.com, gong.chen@linux.intel.com, vasilis.liaskovitis@profitbricks.com, lwoodman@redhat.com, Rik van Riel , jweiner@redhat.com, prarit@redhat.com, "x86@kernel.org" , linux-doc@vger.kernel.org, "linux-kernel@vger.kernel.org" , Linux MM , linux-acpi@vger.kernel.org, imtangchen@gmail.com, Zhang Yanfei , Tang Chen On Wed, 2013-10-09 at 14:14 -0700, H. Peter Anvin wrote: > On 10/09/2013 02:11 PM, Tejun Heo wrote: > > Hello, Toshi. > > > > On Wed, Oct 09, 2013 at 02:58:31PM -0600, Toshi Kani wrote: > >> Let's not assume that memory hotplug is always a niche feature for huge > >> & special systems. It may be a niche to begin with, but it could be > >> supported on VMs, which allows anyone to use. Vasilis has been working > >> on KVM to support memory hotplug. > > > > I'm not saying hotplug will always be niche. I'm saying the approach > > we're currently taking is. It seems fairly inflexible to hang the > > whole thing on NUMA nodes. What does the planned kvm support do? > > Splitting SRAT nodes so that it can do both actual NUMA node > > distribution and hotplug granuliarity? IIRC I asked a couple times > > what the long term plan was for this feature and there doesn't seem to > > be any road map for this thing to become a full solution. Unless I > > misunderstood, this is more of "let's put out the fire as there > > already are (or gonna be) machines which can do it" kinda thing, which > > is fine too. My point is that it doesn't make a lot of sense to > > change boot sequence invasively to accomodate that. > > > > I would also argue that in the VM scenario -- and arguable even in the > hardware scenario -- the right thing is to not expose the flexible > memory in the e820/EFI tables, and instead have it hotadded (possibly > *immediately* so) on boot. This avoids both the boot time funnies as > well as the scaling issues with metadata. That's a good idea! It will work just fine if firmware is written in such a way. However, since the most (if not all) firmware integrates and exposes all memory at boot, we still need to support this regular scenario as well. > The whole reason for VMs wanting this is because ballooning doesn't > scale with regards to metadata. Agreed. Thanks, -Toshi -- 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