From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lai Jiangshan Subject: Re: [PATCH v2 0/4] Fix accessed bit tracking Date: Mon, 07 Jun 2010 16:43:05 +0800 Message-ID: <4C0CB119.3060903@cn.fujitsu.com> References: <1275894659-17656-1-git-send-email-avi@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from cn.fujitsu.com ([222.73.24.84]:61758 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751521Ab0FGImo (ORCPT ); Mon, 7 Jun 2010 04:42:44 -0400 In-Reply-To: <1275894659-17656-1-git-send-email-avi@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > The kvm mmu synchronizes shadow ptes using the mmu lock, however the cpu > will happily ignore the lock when setting the accessed bit. This can cause > the accessed bit to be lost. Luckily this only results in incorrect page > selection for swap. > Atomic operation is heavy and slow, it hurts performance. Incorrect page selection for swap also hurts performance. I think there are very rare competitions happened and cause the accessed bit to be lost. Since there is no incorrect result when the accessed bit is lost. Is this problem over concern? Lai