Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 28 May 2019 18:45:21 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Jason Wang <jasowang@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>
Cc:     netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v2 1/8] vsock/virtio: limit the memory used per-socket
Message-ID: <20190528164521.k2euedfcmtvvynew@steredhat.homenet.telecomitalia.it>
References: <20190510125843.95587-1-sgarzare@redhat.com>
 <20190510125843.95587-2-sgarzare@redhat.com>
 <3b275b52-63d9-d260-1652-8e8bf7dd679f@redhat.com>
 <20190513172322.vcgenx7xk4v6r2ay@steredhat>
 <f834c9e9-5d0e-8ebb-44e0-6d99b6284e5c@redhat.com>
 <20190514163500.a7moalixvpn5mkcr@steredhat>
 <034a5081-b4fb-011f-b5b7-fbf293c13b23@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <034a5081-b4fb-011f-b5b7-fbf293c13b23@redhat.com>
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, May 15, 2019 at 10:48:44AM +0800, Jason Wang wrote:
> 
> On 2019/5/15 上午12:35, Stefano Garzarella wrote:
> > On Tue, May 14, 2019 at 11:25:34AM +0800, Jason Wang wrote:
> > > On 2019/5/14 上午1:23, Stefano Garzarella wrote:
> > > > On Mon, May 13, 2019 at 05:58:53PM +0800, Jason Wang wrote:
> > > > > On 2019/5/10 下午8:58, Stefano Garzarella wrote:
> > > > > > +static struct virtio_vsock_buf *
> > > > > > +virtio_transport_alloc_buf(struct virtio_vsock_pkt *pkt, bool zero_copy)
> > > > > > +{
> > > > > > +	struct virtio_vsock_buf *buf;
> > > > > > +
> > > > > > +	if (pkt->len == 0)
> > > > > > +		return NULL;
> > > > > > +
> > > > > > +	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
> > > > > > +	if (!buf)
> > > > > > +		return NULL;
> > > > > > +
> > > > > > +	/* If the buffer in the virtio_vsock_pkt is full, we can move it to
> > > > > > +	 * the new virtio_vsock_buf avoiding the copy, because we are sure that
> > > > > > +	 * we are not use more memory than that counted by the credit mechanism.
> > > > > > +	 */
> > > > > > +	if (zero_copy && pkt->len == pkt->buf_len) {
> > > > > > +		buf->addr = pkt->buf;
> > > > > > +		pkt->buf = NULL;
> > > > > > +	} else {
> > > > > Is the copy still needed if we're just few bytes less? We meet similar issue
> > > > > for virito-net, and virtio-net solve this by always copy first 128bytes for
> > > > > big packets.
> > > > > 
> > > > > See receive_big()
> > > > I'm seeing, It is more sophisticated.
> > > > IIUC, virtio-net allocates a sk_buff with 128 bytes of buffer, then copies the
> > > > first 128 bytes, then adds the buffer used to receive the packet as a frag to
> > > > the skb.
> > > 
> > > Yes and the point is if the packet is smaller than 128 bytes the pages will
> > > be recycled.
> > > 
> > > 
> > So it's avoid the overhead of allocation of a large buffer. I got it.
> > 
> > Just a curiosity, why the threshold is 128 bytes?
> 
> 
> From its name (GOOD_COPY_LEN), I think it just a value that won't lose much
> performance, e.g the size two cachelines.
> 

Jason, Stefan,
since I'm removing the patches to increase the buffers to 64 KiB and I'm
adding a threshold for small packets, I would simplify this patch,
removing the new buffer allocation and copying small packets into the
buffers already queued (if there is a space).
In this way, I should solve the issue of 1 byte packets.

Do you think could be better?

Thanks,
Stefano