From patchwork Wed Apr 28 09:50:36 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Takuya Yoshikawa X-Patchwork-Id: 95644 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by demeter.kernel.org (8.14.3/8.14.3) with ESMTP id o3S9ktN5029294 for ; Wed, 28 Apr 2010 09:46:55 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753103Ab0D1Jqx (ORCPT ); Wed, 28 Apr 2010 05:46:53 -0400 Received: from serv2.oss.ntt.co.jp ([222.151.198.100]:35532 "EHLO serv2.oss.ntt.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750831Ab0D1Jqw (ORCPT ); Wed, 28 Apr 2010 05:46:52 -0400 Received: from serv2.oss.ntt.co.jp (localhost [127.0.0.1]) by serv2.oss.ntt.co.jp (Postfix) with ESMTP id 8255A248258; Wed, 28 Apr 2010 18:46:50 +0900 (JST) Received: from serv1.oss.ntt.co.jp (serv1.oss.ntt.co.jp [172.19.0.2]) by serv2.oss.ntt.co.jp (Postfix) with ESMTP id 6FE612481B5; Wed, 28 Apr 2010 18:46:50 +0900 (JST) Received: from yshtky3.kern.oss.ntt.co.jp (unknown [172.17.1.128]) by serv1.oss.ntt.co.jp (Postfix) with SMTP id 5531C11C00B; Wed, 28 Apr 2010 18:46:50 +0900 (JST) Date: Wed, 28 Apr 2010 18:50:36 +0900 From: Takuya Yoshikawa To: avi@redhat.com, mtosatti@redhat.com Cc: kvm@vger.kernel.org Subject: [PATCH v2] KVM: x86: avoid unnecessary bitmap allocation when memslot is clean Message-Id: <20100428185036.5beb8a9e.yoshikawa.takuya@oss.ntt.co.jp> In-Reply-To: <20100426185657.7f68c3ad.yoshikawa.takuya@oss.ntt.co.jp> References: <20100426185657.7f68c3ad.yoshikawa.takuya@oss.ntt.co.jp> X-Mailer: Sylpheed 2.6.0 (GTK+ 2.16.1; i486-pc-linux-gnu) Mime-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.3 (demeter.kernel.org [140.211.167.41]); Wed, 28 Apr 2010 09:46:55 +0000 (UTC) === Although we always allocate a new dirty bitmap in x86's get_dirty_log(), it is only used as a zero-source of copy_to_user() and freed right after that when memslot is clean. This patch uses clear_user() instead of doing this unnecessary zero-source allocation. Performance improvement: as we can expect easily, the time needed to allocate a bitmap is completely reduced. In my test, the improved ioctl was about 4 to 10 times faster than the original one for clean slots. Furthermore, reducing memory allocations and copies will produce good effects to caches too. Signed-off-by: Takuya Yoshikawa --- arch/x86/kvm/x86.c | 37 +++++++++++++++++++++++-------------- 1 files changed, 23 insertions(+), 14 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6b2ce1d..b95a211 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2744,7 +2744,6 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot; unsigned long n; unsigned long is_dirty = 0; - unsigned long *dirty_bitmap = NULL; mutex_lock(&kvm->slots_lock); @@ -2759,27 +2758,30 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, n = kvm_dirty_bitmap_bytes(memslot); - r = -ENOMEM; - dirty_bitmap = vmalloc(n); - if (!dirty_bitmap) - goto out; - memset(dirty_bitmap, 0, n); - for (i = 0; !is_dirty && i < n/sizeof(long); i++) is_dirty = memslot->dirty_bitmap[i]; /* If nothing is dirty, don't bother messing with page tables. */ if (is_dirty) { struct kvm_memslots *slots, *old_slots; + unsigned long *dirty_bitmap; spin_lock(&kvm->mmu_lock); kvm_mmu_slot_remove_write_access(kvm, log->slot); spin_unlock(&kvm->mmu_lock); - slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL); - if (!slots) - goto out_free; + r = -ENOMEM; + dirty_bitmap = vmalloc(n); + if (!dirty_bitmap) + goto out; + memset(dirty_bitmap, 0, n); + r = -ENOMEM; + slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL); + if (!slots) { + vfree(dirty_bitmap); + goto out; + } memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots)); slots->memslots[log->slot].dirty_bitmap = dirty_bitmap; @@ -2788,13 +2790,20 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, synchronize_srcu_expedited(&kvm->srcu); dirty_bitmap = old_slots->memslots[log->slot].dirty_bitmap; kfree(old_slots); + + r = -EFAULT; + if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) { + vfree(dirty_bitmap); + goto out; + } + vfree(dirty_bitmap); + } else { + r = -EFAULT; + if (clear_user(log->dirty_bitmap, n)) + goto out; } r = 0; - if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) - r = -EFAULT; -out_free: - vfree(dirty_bitmap); out: mutex_unlock(&kvm->slots_lock); return r;