From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net-next 3/3] vhost: access vq metadata through kernel virtual address Date: Thu, 13 Dec 2018 16:58:04 -0500 Message-ID: <20181213165731-mutt-send-email-mst__6558.53258581391$1544738189$gmane$org@kernel.org> References: <20181213101022.12475-1-jasowang@redhat.com> <20181213101022.12475-4-jasowang@redhat.com> <20181213102713-mutt-send-email-mst@kernel.org> <20181213211840.GC18692@char.us.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20181213211840.GC18692@char.us.oracle.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Konrad Rzeszutek Wilk Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Thu, Dec 13, 2018 at 04:18:40PM -0500, Konrad Rzeszutek Wilk wrote: > .giant snip.. > > > + npinned = get_user_pages_fast(uaddr, npages, write, pages); > > > + if (npinned != npages) > > > + goto err; > > > + > > > > As I said I have doubts about the whole approach, but this > > implementation in particular isn't a good idea > > as it keeps the page around forever. > > So no THP, no NUMA rebalancing, userspace-controlled > > amount of memory locked up and not accounted for. > > > > Don't get me wrong it's a great patch in an ideal world. > > But then in an ideal world no barriers smap etc are necessary at all. > > So .. suggestions on how this could be accepted? As in other ways > where we still get vmap and the issues you mentioned are not troubling you? > > Thanks! I'd suggest leave vmap alone and find ways to speed up accesses that can fault. -- MST