From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f181.google.com (mail-we0-f181.google.com [74.125.82.181]) by kanga.kvack.org (Postfix) with ESMTP id C66A96B0036 for ; Thu, 19 Jun 2014 05:20:37 -0400 (EDT) Received: by mail-we0-f181.google.com with SMTP id q59so1993736wes.26 for ; Thu, 19 Jun 2014 02:20:37 -0700 (PDT) Received: from mail-wi0-f176.google.com (mail-wi0-f176.google.com [209.85.212.176]) by mx.google.com with ESMTPS id ni12si4837095wic.49.2014.06.19.02.20.35 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 19 Jun 2014 02:20:36 -0700 (PDT) Received: by mail-wi0-f176.google.com with SMTP id n3so8990834wiv.3 for ; Thu, 19 Jun 2014 02:20:35 -0700 (PDT) Date: Thu, 19 Jun 2014 12:20:32 +0300 From: Gleb Natapov Subject: Re: [RFC PATCH 1/1] Move two pinned pages to non-movable node in kvm. Message-ID: <20140619092031.GA429@minantech.com> References: <1403070600-6083-1-git-send-email-tangchen@cn.fujitsu.com> <20140618061230.GA10948@minantech.com> <53A136C4.5070206@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53A136C4.5070206@cn.fujitsu.com> Sender: owner-linux-mm@kvack.org List-ID: To: Tang Chen Cc: pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, mgorman@suse.de, yinghai@kernel.org, isimatu.yasuaki@jp.fujitsu.com, guz.fnst@cn.fujitsu.com, laijs@cn.fujitsu.com, kvm@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org, mtosatti@redhat.com CCing Marcelo, On Wed, Jun 18, 2014 at 02:50:44PM +0800, Tang Chen wrote: > Hi Gleb, > > Thanks for the quick reply. Please see below. > > On 06/18/2014 02:12 PM, Gleb Natapov wrote: > >On Wed, Jun 18, 2014 at 01:50:00PM +0800, Tang Chen wrote: > >>[Questions] > >>And by the way, would you guys please answer the following questions for me ? > >> > >>1. What's the ept identity pagetable for ? Only one page is enough ? > >> > >>2. Is the ept identity pagetable only used in realmode ? > >> Can we free it once the guest is up (vcpu in protect mode)? > >> > >>3. Now, ept identity pagetable is allocated in qemu userspace. > >> Can we allocate it in kernel space ? > >What would be the benefit? > > I think the benefit is we can hot-remove the host memory a kvm guest > is using. > > For now, only memory in ZONE_MOVABLE can be migrated/hot-removed. And the > kernel > will never use ZONE_MOVABLE memory. So if we can allocate these two pages in > kernel space, we can pin them without any trouble. When doing memory > hot-remove, > the kernel will not try to migrate these two pages. But we can do that by other means, no? The patch you've sent for instance. > > > > >> > >>4. If I want to migrate these two pages, what do you think is the best way ? > >> > >I answered most of those here: http://www.mail-archive.com/kvm@vger.kernel.org/msg103718.html > > I'm sorry I must missed this email. > > Seeing your advice, we can unpin these two pages and repin them in the next > EPT violation. > So about this problem, which solution would you prefer, allocate these two > pages in kernel > space, or migrate them before memory hot-remove ? > > I think the first solution is simpler. But I'm not quite sure if there is > any other pages > pinned in memory. If we have the same problem with other kvm pages, I think > it is better to > solve it in the second way. > > What do you think ? Remove pinning is preferable. In fact looks like for identity pagetable it should be trivial, just don't pin. APIC access page is a little bit more complicated since its physical address needs to be tracked to be updated in VMCS. -- Gleb. -- 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