From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb_others Date: Tue, 01 May 2012 17:14:52 +0200 Message-ID: <1335885292.13683.150.camel@twins> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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: Avi Kivity Return-path: In-Reply-To: <4F9FD337.5010908@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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. > 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.