linux-kernel - Re: [PATCH net-next 04/11] tuntap: simplify error handling in tun_build

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Date:   Fri, 7 Sep 2018 10:17:35 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 04/11] tuntap: simplify error handling in
 tun_build_skb()

On Fri, Sep 07, 2018 at 11:22:00AM +0800, Jason Wang wrote:
> > > @@ -1668,6 +1668,9 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
> > >   	if (copied != len)
> > >   		return ERR_PTR(-EFAULT);
> > > +	get_page(alloc_frag->page);
> > > +	alloc_frag->offset += buflen;
> > > +
> > This adds an atomic op on XDP_DROP which is a data path
> > operation for some workloads.
> 
> Yes, I have patch on top to amortize this, the idea is to have a very big
> refcount once after the frag was allocated and maintain a bias and decrease
> them all when allocating new frags.'

Why bother with refcounting for a drop though? It should be simple.

-- 
MST