From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 3/4] KVM: Count the number of dirty pages for dirty logging Date: Mon, 14 Nov 2011 12:24:19 +0200 Message-ID: <4EC0EC53.2020100@redhat.com> References: <20111114182041.43570cdf.yoshikawa.takuya@oss.ntt.co.jp> <20111114182334.f57fbeae.yoshikawa.takuya@oss.ntt.co.jp> <4EC0E85F.80004@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: mtosatti@redhat.com, kvm@vger.kernel.org, takuya.yoshikawa@gmail.com To: Takuya Yoshikawa Return-path: Received: from mx1.redhat.com ([209.132.183.28]:2971 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753324Ab1KNKYY (ORCPT ); Mon, 14 Nov 2011 05:24:24 -0500 In-Reply-To: <4EC0E85F.80004@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 11/14/2011 12:07 PM, Avi Kivity wrote: > On 11/14/2011 11:23 AM, Takuya Yoshikawa wrote: > > Needed for the next patch which uses this number to decide how to write > > protect a slot. > > > > /* If nothing is dirty, don't bother messing with page tables. */ > > - if (is_dirty) { > > + if (memslot->nr_dirty_pages) { > > struct kvm_memslots *slots, *old_slots; > > unsigned long *dirty_bitmap; > > > > @@ -3504,6 +3500,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, > > goto out; > > memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots)); > > slots->memslots[log->slot].dirty_bitmap = dirty_bitmap; > > + slots->memslots[log->slot].nr_dirty_pages = 0; > > slots->generation++; > > > > #endif /* !CONFIG_S390 */ > > @@ -1491,7 +1492,8 @@ void mark_page_dirty_in_slot(struct kvm *kvm, struct kvm_memory_slot *memslot, > > if (memslot && memslot->dirty_bitmap) { > > unsigned long rel_gfn = gfn - memslot->base_gfn; > > > > - __set_bit_le(rel_gfn, memslot->dirty_bitmap); > > + if (!__test_and_set_bit_le(rel_gfn, memslot->dirty_bitmap)) > > + memslot->nr_dirty_pages++; > > } > > } > > > > The two assignments to ->nr_dirty_pages can race, no? Nothing protects it. > er, it can't, it's before the rcu_assign_pointer(). -- error compiling committee.c: too many argumen ts to function