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Date: Mon, 16 Apr 2012 16:25:20 +0300 From: "Michael S. Tsirkin" <mst@...hat.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org, xma@...ibm.com, davem@...emloft.net, linux-kernel@...r.kernel.org, ebiederm@...ssion.com Subject: Re: [PATCH 2/6] macvtap: zerocopy: fix truesize underestimation 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 <jasowang@...hat.com> > > > > 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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