From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 2/6] macvtap: zerocopy: fix truesize underestimation Date: Mon, 16 Apr 2012 16:25:20 +0300 Message-ID: <20120416132520.GA13113@redhat.com> References: <20120416060749.14140.19433.stgit@intel-e5620-16-2.englab.nay.redhat.com> <20120416060758.14140.40252.stgit@intel-e5620-16-2.englab.nay.redhat.com> <20120416071423.GA25396@redhat.com> <1334566193.28012.66.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jason Wang , netdev@vger.kernel.org, xma@us.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, ebiederm@xmission.com To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: <1334566193.28012.66.camel@edumazet-glaptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, Apr 16, 2012 at 10:49:53AM +0200, Eric Dumazet wrote: > On Mon, 2012-04-16 at 10:14 +0300, Michael S. Tsirkin wrote: > > On Mon, Apr 16, 2012 at 02:07:59PM +0800, Jason Wang wrote: > > > As the skb fragment were pinned/built from user pages, we should > > > account the page instead of length for truesize. > > > > > > Signed-off-by: Jason Wang > > > > I'm not sure this is right: the skb does *not* consume the > > whole page, userspace uses the rest of the page > > for other skbs. So we'll end up accounting for the > > same page twice. > > Eric, what's the right thing to do here in your opinion? > > Problem is we dont know for sure userspace wont free pages right after > this syscall. So an evil application could consume more kernel memory > than what socket limit allowed. > > Its same problem with vmsplice(mem -> pipe) + splice(pipe -> socket) > > When we clone skb with frags, resulting skb will have same truesize, > even if the pages are shared ... > I see, thanks for the clarification. -- MST