From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb_others Date: Tue, 01 May 2012 18:36:20 +0300 Message-ID: <4FA002F4.8000508@redhat.com> References: <20120427161727.27082.43096.stgit@abhimanyu> <20120427162401.27082.59387.stgit@abhimanyu> <4F9D32B4.8040002@redhat.com> <1335865176.13683.120.camel@twins> <4F9FBF38.2060903@redhat.com> <1335869827.13683.133.camel@twins> <4F9FD337.5010908@redhat.com> <1335885292.13683.150.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Nikunj A. Dadhania" , mingo@elte.hu, jeremy@goop.org, mtosatti@redhat.com, kvm@vger.kernel.org, x86@kernel.org, vatsa@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, hpa@zytor.com To: Peter Zijlstra Return-path: In-Reply-To: <1335885292.13683.150.camel@twins> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/01/2012 06:14 PM, Peter Zijlstra wrote: > On Tue, 2012-05-01 at 15:12 +0300, Avi Kivity wrote: > > > > What's changed is not gup_fast() but the performance of munmap(), > > exit(), and exec(), no? > > If it is indeed cache related like you suggested earlier, it would be > the allocation side of things, like fork()/mmap() that suffer since > there's fewer hot pages about, but yes, anything creating/destroying > page-tables. Right. > > > What bounds the amount of memory waiting to be freed during an rcu grace > > period? > > Most RCU implementations don't have limits, so that could be quite a > lot. I think preemptible RCU has a batch limit at which point it tries > rather hard to force a grace period, but I'm not sure if even that > provides a hard limit. > > Practically though, I haven't had reports of PPC/Sparc going funny > because of this. It could be considered a DoS if a user is able to free page tables faster than rcu is able to recycle them, possibly triggering the oom killer (should that force a grace period before firing from the hip?) -- error compiling committee.c: too many arguments to function