From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olaf Hering Subject: Re: some questions of IO ring in xenpaging Date: Mon, 5 Sep 2011 13:31:55 +0200 Message-ID: <20110905113154.GA29099@aepfle.de> References: <20110901101525.GA3258@aepfle.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <20110901101525.GA3258@aepfle.de> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: zhen shi Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On Thu, Sep 01, Olaf Hering wrote: > On Thu, Sep 01, zhen shi wrote: > > > Hi Olaf -- > > > > I have two questions to ask you about xenpaging. > > 1) When guest os causes page_fault for the accessed page is paging_out > > or paged, it will execute p2m_mem_paging_populate(). and in > > p2m_mem_paging_populate() it will first check if the ring is full. > > when I ran with domU suse11 4G memory and 8vcpus, I found there will > > be a corruption in checking the ring. > > For example, if 4vcpus are met with page faults when they access > > different pages, and there is only four free-requests for the ring. > > and then they call p2m_mem_paging_populate(),and execute > > mem_event_check_ring(d) at the same time.All will find ring is not > > full,and will fill the requests. It will cause the latter request to > > cover the front request. > > and I think there should a lock before the mem_event_check_ring(d), > > and normally it unlock after mem_event_put_request(d, &req). > > You can review the attached doc of xenpaging_IO_ring.txt to see if my > > opnion is right. > > Yes, you are right. > I think mem_event_check_ring() should reserve a reference, and > mem_event_put_request() should use that reference. > mem_sharing_alloc_page() even has a comment that this should be done. Try this patch. It implements some ref counting. http://lists.xensource.com/archives/html/xen-devel/2011-09/msg00189.html Olaf