Linux Virtualization - May 2019 - [PATCH v2 1/8] vsock/virtio: limit the memory used per-socket

On 2019/5/14 ??1:23, Stefano Garzarella wrote:
> On Mon, May 13, 2019 at 05:58:53PM +0800, Jason Wang wrote:
>> On 2019/5/10 ??8:58, Stefano Garzarella wrote:
>>> Since virtio-vsock was introduced, the buffers filled by the host
>>> and pushed to the guest using the vring, are directly queued in
>>> a per-socket list avoiding to copy it.
>>> These buffers are preallocated by the guest with a fixed
>>> size (4 KB).
>>>
>>> The maximum amount of memory used by each socket should be
>>> controlled by the credit mechanism.
>>> The default credit available per-socket is 256 KB, but if we use
>>> only 1 byte per packet, the guest can queue up to 262144 of 4 KB
>>> buffers, using up to 1 GB of memory per-socket. In addition, the
>>> guest will continue to fill the vring with new 4 KB free buffers
>>> to avoid starvation of her sockets.
>>>
>>> This patch solves this issue copying the payload in a new buffer.
>>> Then it is queued in the per-socket list, and the 4KB buffer used
>>> by the host is freed.
>>>
>>> In this way, the memory used by each socket respects the credit
>>> available, and we still avoid starvation, paying the cost of an
>>> extra memory copy. When the buffer is completely full we do a
>>> "zero-copy", moving the buffer directly in the per-socket
list.
>>
>> I wonder in the long run we should use generic socket accouting
mechanism
>> provided by kernel (e.g socket, skb, sndbuf, recvbug, truesize) instead
of
>> vsock specific thing to avoid duplicating efforts.
> I agree, the idea is to switch to sk_buff but this should require an huge
> change. If we will use the virtio-net datapath, it will become simpler.

Yes, unix domain socket is one example that uses general skb and socket 
structure. And we probably need some kind of socket pair on host. Using 
socket can also simplify the unification with vhost-net which depends on 
the socket proto_ops to work. I admit it's a huge change probably, we 
can do it gradually.

>>
>>> Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
>>> ---
>>>    drivers/vhost/vsock.c                   |  2 +
>>>    include/linux/virtio_vsock.h            |  8 +++
>>>    net/vmw_vsock/virtio_transport.c        |  1 +
>>>    net/vmw_vsock/virtio_transport_common.c | 95
++++++++++++++++++-------
>>>    4 files changed, 81 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>>> index bb5fc0e9fbc2..7964e2daee09 100644
>>> --- a/drivers/vhost/vsock.c
>>> +++ b/drivers/vhost/vsock.c
>>> @@ -320,6 +320,8 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue
*vq,
>>>    		return NULL;
>>>    	}
>>> +	pkt->buf_len = pkt->len;
>>> +
>>>    	nbytes = copy_from_iter(pkt->buf, pkt->len,
&iov_iter);
>>>    	if (nbytes != pkt->len) {
>>>    		vq_err(vq, "Expected %u byte payload, got %zu
bytes\n",
>>> diff --git a/include/linux/virtio_vsock.h
b/include/linux/virtio_vsock.h
>>> index e223e2632edd..345f04ee9193 100644
>>> --- a/include/linux/virtio_vsock.h
>>> +++ b/include/linux/virtio_vsock.h
>>> @@ -54,9 +54,17 @@ struct virtio_vsock_pkt {
>>>    	void *buf;
>>>    	u32 len;
>>>    	u32 off;
>>> +	u32 buf_len;
>>>    	bool reply;
>>>    };
>>> +struct virtio_vsock_buf {
>>> +	struct list_head list;
>>> +	void *addr;
>>> +	u32 len;
>>> +	u32 off;
>>> +};
>>> +
>>>    struct virtio_vsock_pkt_info {
>>>    	u32 remote_cid, remote_port;
>>>    	struct vsock_sock *vsk;
>>> diff --git a/net/vmw_vsock/virtio_transport.c
b/net/vmw_vsock/virtio_transport.c
>>> index 15eb5d3d4750..af1d2ce12f54 100644
>>> --- a/net/vmw_vsock/virtio_transport.c
>>> +++ b/net/vmw_vsock/virtio_transport.c
>>> @@ -280,6 +280,7 @@ static void virtio_vsock_rx_fill(struct
virtio_vsock *vsock)
>>>    			break;
>>>    		}
>>> +		pkt->buf_len = buf_len;
>>>    		pkt->len = buf_len;
>>>    		sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
>>> diff --git a/net/vmw_vsock/virtio_transport_common.c
b/net/vmw_vsock/virtio_transport_common.c
>>> index 602715fc9a75..0248d6808755 100644
>>> --- a/net/vmw_vsock/virtio_transport_common.c
>>> +++ b/net/vmw_vsock/virtio_transport_common.c
>>> @@ -65,6 +65,9 @@ virtio_transport_alloc_pkt(struct
virtio_vsock_pkt_info *info,
>>>    		pkt->buf = kmalloc(len, GFP_KERNEL);
>>>    		if (!pkt->buf)
>>>    			goto out_pkt;
>>> +
>>> +		pkt->buf_len = len;
>>> +
>>>    		err = memcpy_from_msg(pkt->buf, info->msg, len);
>>>    		if (err)
>>>    			goto out;
>>> @@ -86,6 +89,46 @@ virtio_transport_alloc_pkt(struct
virtio_vsock_pkt_info *info,
>>>    	return NULL;
>>>    }
>>> +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.

>
> Do you suggest to implement something similar, or for now we can use my
> approach and if we will merge the datapath we can reuse the virtio-net
> approach?

I think we need a better threshold. If I understand the patch correctly, 
we will do copy unless the packet is 64K when guest is doing receiving. 
1 byte packet is indeed a problem, but we need to solve it without 
losing too much performance.

Thanks

>
> Thanks,
> Stefano

On 2019/5/14 ??11:25, Jason Wang wrote:
>
> On 2019/5/14 ??1:23, Stefano Garzarella wrote:
>> On Mon, May 13, 2019 at 05:58:53PM +0800, Jason Wang wrote:
>>> On 2019/5/10 ??8:58, Stefano Garzarella wrote:
>>>> Since virtio-vsock was introduced, the buffers filled by the
host
>>>> and pushed to the guest using the vring, are directly queued in
>>>> a per-socket list avoiding to copy it.
>>>> These buffers are preallocated by the guest with a fixed
>>>> size (4 KB).
>>>>
>>>> The maximum amount of memory used by each socket should be
>>>> controlled by the credit mechanism.
>>>> The default credit available per-socket is 256 KB, but if we
use
>>>> only 1 byte per packet, the guest can queue up to 262144 of 4
KB
>>>> buffers, using up to 1 GB of memory per-socket. In addition,
the
>>>> guest will continue to fill the vring with new 4 KB free
buffers
>>>> to avoid starvation of her sockets.
>>>>
>>>> This patch solves this issue copying the payload in a new
buffer.
>>>> Then it is queued in the per-socket list, and the 4KB buffer
used
>>>> by the host is freed.
>>>>
>>>> In this way, the memory used by each socket respects the credit
>>>> available, and we still avoid starvation, paying the cost of an
>>>> extra memory copy. When the buffer is completely full we do a
>>>> "zero-copy", moving the buffer directly in the
per-socket list.
>>>
>>> I wonder in the long run we should use generic socket accouting 
>>> mechanism
>>> provided by kernel (e.g socket, skb, sndbuf, recvbug, truesize) 
>>> instead of
>>> vsock specific thing to avoid duplicating efforts.
>> I agree, the idea is to switch to sk_buff but this should require an 
>> huge
>> change. If we will use the virtio-net datapath, it will become simpler.
>
>
> Yes, unix domain socket is one example that uses general skb and 
> socket structure. And we probably need some kind of socket pair on 
> host. Using socket can also simplify the unification with vhost-net 
> which depends on the socket proto_ops to work. I admit it's a huge 
> change probably, we can do it gradually.
>
>
>>>
>>>> Signed-off-by: Stefano Garzarella <sgarzare at
redhat.com>
>>>> ---
>>>> ?? drivers/vhost/vsock.c?????????????????? |? 2 +
>>>> ?? include/linux/virtio_vsock.h??????????? |? 8 +++
>>>> ?? net/vmw_vsock/virtio_transport.c??????? |? 1 +
>>>> ?? net/vmw_vsock/virtio_transport_common.c | 95 
>>>> ++++++++++++++++++-------
>>>> ?? 4 files changed, 81 insertions(+), 25 deletions(-)
>>>>
>>>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>>>> index bb5fc0e9fbc2..7964e2daee09 100644
>>>> --- a/drivers/vhost/vsock.c
>>>> +++ b/drivers/vhost/vsock.c
>>>> @@ -320,6 +320,8 @@ vhost_vsock_alloc_pkt(struct
vhost_virtqueue *vq,
>>>> ?????????? return NULL;
>>>> ?????? }
>>>> +??? pkt->buf_len = pkt->len;
>>>> +
>>>> ?????? nbytes = copy_from_iter(pkt->buf, pkt->len,
&iov_iter);
>>>> ?????? if (nbytes != pkt->len) {
>>>> ?????????? vq_err(vq, "Expected %u byte payload, got %zu
bytes\n",
>>>> diff --git a/include/linux/virtio_vsock.h 
>>>> b/include/linux/virtio_vsock.h
>>>> index e223e2632edd..345f04ee9193 100644
>>>> --- a/include/linux/virtio_vsock.h
>>>> +++ b/include/linux/virtio_vsock.h
>>>> @@ -54,9 +54,17 @@ struct virtio_vsock_pkt {
>>>> ?????? void *buf;
>>>> ?????? u32 len;
>>>> ?????? u32 off;
>>>> +??? u32 buf_len;
>>>> ?????? bool reply;
>>>> ?? };
>>>> +struct virtio_vsock_buf {
>>>> +??? struct list_head list;
>>>> +??? void *addr;
>>>> +??? u32 len;
>>>> +??? u32 off;
>>>> +};
>>>> +
>>>> ?? struct virtio_vsock_pkt_info {
>>>> ?????? u32 remote_cid, remote_port;
>>>> ?????? struct vsock_sock *vsk;
>>>> diff --git a/net/vmw_vsock/virtio_transport.c 
>>>> b/net/vmw_vsock/virtio_transport.c
>>>> index 15eb5d3d4750..af1d2ce12f54 100644
>>>> --- a/net/vmw_vsock/virtio_transport.c
>>>> +++ b/net/vmw_vsock/virtio_transport.c
>>>> @@ -280,6 +280,7 @@ static void virtio_vsock_rx_fill(struct 
>>>> virtio_vsock *vsock)
>>>> ?????????????? break;
>>>> ?????????? }
>>>> +??????? pkt->buf_len = buf_len;
>>>> ?????????? pkt->len = buf_len;
>>>> ?????????? sg_init_one(&hdr, &pkt->hdr,
sizeof(pkt->hdr));
>>>> diff --git a/net/vmw_vsock/virtio_transport_common.c 
>>>> b/net/vmw_vsock/virtio_transport_common.c
>>>> index 602715fc9a75..0248d6808755 100644
>>>> --- a/net/vmw_vsock/virtio_transport_common.c
>>>> +++ b/net/vmw_vsock/virtio_transport_common.c
>>>> @@ -65,6 +65,9 @@ virtio_transport_alloc_pkt(struct 
>>>> virtio_vsock_pkt_info *info,
>>>> ?????????? pkt->buf = kmalloc(len, GFP_KERNEL);
>>>> ?????????? if (!pkt->buf)
>>>> ?????????????? goto out_pkt;
>>>> +
>>>> +??????? pkt->buf_len = len;
>>>> +
>>>> ?????????? err = memcpy_from_msg(pkt->buf, info->msg,
len);
>>>> ?????????? if (err)
>>>> ?????????????? goto out;
>>>> @@ -86,6 +89,46 @@ virtio_transport_alloc_pkt(struct 
>>>> virtio_vsock_pkt_info *info,
>>>> ?????? return NULL;
>>>> ?? }
>>>> +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. 

To be clear, this only work if you use order 0 page instead of a large 
buffer that is allocated through kmalloc(). Another requirement for 
order 0 page.

Thanks

On Tue, May 14, 2019 at 11:25:34AM +0800, Jason Wang
wrote:
> 
> On 2019/5/14 ??1:23, Stefano Garzarella wrote:
> > On Mon, May 13, 2019 at 05:58:53PM +0800, Jason Wang wrote:
> > > On 2019/5/10 ??8:58, Stefano Garzarella wrote:
> > > > Since virtio-vsock was introduced, the buffers filled by the
host
> > > > and pushed to the guest using the vring, are directly queued
in
> > > > a per-socket list avoiding to copy it.
> > > > These buffers are preallocated by the guest with a fixed
> > > > size (4 KB).
> > > > 
> > > > The maximum amount of memory used by each socket should be
> > > > controlled by the credit mechanism.
> > > > The default credit available per-socket is 256 KB, but if we
use
> > > > only 1 byte per packet, the guest can queue up to 262144 of
4 KB
> > > > buffers, using up to 1 GB of memory per-socket. In addition,
the
> > > > guest will continue to fill the vring with new 4 KB free
buffers
> > > > to avoid starvation of her sockets.
> > > > 
> > > > This patch solves this issue copying the payload in a new
buffer.
> > > > Then it is queued in the per-socket list, and the 4KB buffer
used
> > > > by the host is freed.
> > > > 
> > > > In this way, the memory used by each socket respects the
credit
> > > > available, and we still avoid starvation, paying the cost of
an
> > > > extra memory copy. When the buffer is completely full we do
a
> > > > "zero-copy", moving the buffer directly in the
per-socket list.
> > > 
> > > I wonder in the long run we should use generic socket accouting
mechanism
> > > provided by kernel (e.g socket, skb, sndbuf, recvbug, truesize)
instead of
> > > vsock specific thing to avoid duplicating efforts.
> > I agree, the idea is to switch to sk_buff but this should require an
huge
> > change. If we will use the virtio-net datapath, it will become
simpler.
> 
> 
> Yes, unix domain socket is one example that uses general skb and socket
> structure. And we probably need some kind of socket pair on host. Using
> socket can also simplify the unification with vhost-net which depends on
the
> socket proto_ops to work. I admit it's a huge change probably, we can
do it
> gradually.
> 
Yes, I also prefer to do this change gradually :)
> 
> > > 
> > > > Signed-off-by: Stefano Garzarella <sgarzare at
redhat.com>
> > > > ---
> > > >    drivers/vhost/vsock.c                   |  2 +
> > > >    include/linux/virtio_vsock.h            |  8 +++
> > > >    net/vmw_vsock/virtio_transport.c        |  1 +
> > > >    net/vmw_vsock/virtio_transport_common.c | 95
++++++++++++++++++-------
> > > >    4 files changed, 81 insertions(+), 25 deletions(-)
> > > > 
> > > > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > > > index bb5fc0e9fbc2..7964e2daee09 100644
> > > > --- a/drivers/vhost/vsock.c
> > > > +++ b/drivers/vhost/vsock.c
> > > > @@ -320,6 +320,8 @@ vhost_vsock_alloc_pkt(struct
vhost_virtqueue *vq,
> > > >    		return NULL;
> > > >    	}
> > > > +	pkt->buf_len = pkt->len;
> > > > +
> > > >    	nbytes = copy_from_iter(pkt->buf, pkt->len,
&iov_iter);
> > > >    	if (nbytes != pkt->len) {
> > > >    		vq_err(vq, "Expected %u byte payload, got %zu
bytes\n",
> > > > diff --git a/include/linux/virtio_vsock.h
b/include/linux/virtio_vsock.h
> > > > index e223e2632edd..345f04ee9193 100644
> > > > --- a/include/linux/virtio_vsock.h
> > > > +++ b/include/linux/virtio_vsock.h
> > > > @@ -54,9 +54,17 @@ struct virtio_vsock_pkt {
> > > >    	void *buf;
> > > >    	u32 len;
> > > >    	u32 off;
> > > > +	u32 buf_len;
> > > >    	bool reply;
> > > >    };
> > > > +struct virtio_vsock_buf {
> > > > +	struct list_head list;
> > > > +	void *addr;
> > > > +	u32 len;
> > > > +	u32 off;
> > > > +};
> > > > +
> > > >    struct virtio_vsock_pkt_info {
> > > >    	u32 remote_cid, remote_port;
> > > >    	struct vsock_sock *vsk;
> > > > diff --git a/net/vmw_vsock/virtio_transport.c
b/net/vmw_vsock/virtio_transport.c
> > > > index 15eb5d3d4750..af1d2ce12f54 100644
> > > > --- a/net/vmw_vsock/virtio_transport.c
> > > > +++ b/net/vmw_vsock/virtio_transport.c
> > > > @@ -280,6 +280,7 @@ static void virtio_vsock_rx_fill(struct
virtio_vsock *vsock)
> > > >    			break;
> > > >    		}
> > > > +		pkt->buf_len = buf_len;
> > > >    		pkt->len = buf_len;
> > > >    		sg_init_one(&hdr, &pkt->hdr,
sizeof(pkt->hdr));
> > > > diff --git a/net/vmw_vsock/virtio_transport_common.c
b/net/vmw_vsock/virtio_transport_common.c
> > > > index 602715fc9a75..0248d6808755 100644
> > > > --- a/net/vmw_vsock/virtio_transport_common.c
> > > > +++ b/net/vmw_vsock/virtio_transport_common.c
> > > > @@ -65,6 +65,9 @@ virtio_transport_alloc_pkt(struct
virtio_vsock_pkt_info *info,
> > > >    		pkt->buf = kmalloc(len, GFP_KERNEL);
> > > >    		if (!pkt->buf)
> > > >    			goto out_pkt;
> > > > +
> > > > +		pkt->buf_len = len;
> > > > +
> > > >    		err = memcpy_from_msg(pkt->buf, info->msg, len);
> > > >    		if (err)
> > > >    			goto out;
> > > > @@ -86,6 +89,46 @@ virtio_transport_alloc_pkt(struct
virtio_vsock_pkt_info *info,
> > > >    	return NULL;
> > > >    }
> > > > +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?
> > 
> > Do you suggest to implement something similar, or for now we can use
my
> > approach and if we will merge the datapath we can reuse the virtio-net
> > approach?
> 
> 
> I think we need a better threshold. If I understand the patch correctly, we
> will do copy unless the packet is 64K when guest is doing receiving. 1 byte
> packet is indeed a problem, but we need to solve it without losing too much
> performance.
It is correct. I'll try to figure out a better threshold and the usage of
order 0 page.

Thanks again for your advices,
Stefano

On 2019/5/15 ??12:35, Stefano Garzarella wrote:
> On Tue, May 14, 2019 at 11:25:34AM +0800, Jason Wang wrote:
>> On 2019/5/14 ??1:23, Stefano Garzarella wrote:
>>> On Mon, May 13, 2019 at 05:58:53PM +0800, Jason Wang wrote:
>>>> On 2019/5/10 ??8:58, Stefano Garzarella wrote:
>>>>> Since virtio-vsock was introduced, the buffers filled by
the host
>>>>> and pushed to the guest using the vring, are directly
queued in
>>>>> a per-socket list avoiding to copy it.
>>>>> These buffers are preallocated by the guest with a fixed
>>>>> size (4 KB).
>>>>>
>>>>> The maximum amount of memory used by each socket should be
>>>>> controlled by the credit mechanism.
>>>>> The default credit available per-socket is 256 KB, but if
we use
>>>>> only 1 byte per packet, the guest can queue up to 262144 of
4 KB
>>>>> buffers, using up to 1 GB of memory per-socket. In
addition, the
>>>>> guest will continue to fill the vring with new 4 KB free
buffers
>>>>> to avoid starvation of her sockets.
>>>>>
>>>>> This patch solves this issue copying the payload in a new
buffer.
>>>>> Then it is queued in the per-socket list, and the 4KB
buffer used
>>>>> by the host is freed.
>>>>>
>>>>> In this way, the memory used by each socket respects the
credit
>>>>> available, and we still avoid starvation, paying the cost
of an
>>>>> extra memory copy. When the buffer is completely full we do
a
>>>>> "zero-copy", moving the buffer directly in the
per-socket list.
>>>> I wonder in the long run we should use generic socket accouting
mechanism
>>>> provided by kernel (e.g socket, skb, sndbuf, recvbug, truesize)
instead of
>>>> vsock specific thing to avoid duplicating efforts.
>>> I agree, the idea is to switch to sk_buff but this should require
an huge
>>> change. If we will use the virtio-net datapath, it will become
simpler.
>>
>> Yes, unix domain socket is one example that uses general skb and socket
>> structure. And we probably need some kind of socket pair on host. Using
>> socket can also simplify the unification with vhost-net which depends
on the
>> socket proto_ops to work. I admit it's a huge change probably, we
can do it
>> gradually.
>>
> Yes, I also prefer to do this change gradually :)
>
>>>>> Signed-off-by: Stefano Garzarella <sgarzare at
redhat.com>
>>>>> ---
>>>>>     drivers/vhost/vsock.c                   |  2 +
>>>>>     include/linux/virtio_vsock.h            |  8 +++
>>>>>     net/vmw_vsock/virtio_transport.c        |  1 +
>>>>>     net/vmw_vsock/virtio_transport_common.c | 95
++++++++++++++++++-------
>>>>>     4 files changed, 81 insertions(+), 25 deletions(-)
>>>>>
>>>>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>>>>> index bb5fc0e9fbc2..7964e2daee09 100644
>>>>> --- a/drivers/vhost/vsock.c
>>>>> +++ b/drivers/vhost/vsock.c
>>>>> @@ -320,6 +320,8 @@ vhost_vsock_alloc_pkt(struct
vhost_virtqueue *vq,
>>>>>     		return NULL;
>>>>>     	}
>>>>> +	pkt->buf_len = pkt->len;
>>>>> +
>>>>>     	nbytes = copy_from_iter(pkt->buf, pkt->len,
&iov_iter);
>>>>>     	if (nbytes != pkt->len) {
>>>>>     		vq_err(vq, "Expected %u byte payload, got %zu
bytes\n",
>>>>> diff --git a/include/linux/virtio_vsock.h
b/include/linux/virtio_vsock.h
>>>>> index e223e2632edd..345f04ee9193 100644
>>>>> --- a/include/linux/virtio_vsock.h
>>>>> +++ b/include/linux/virtio_vsock.h
>>>>> @@ -54,9 +54,17 @@ struct virtio_vsock_pkt {
>>>>>     	void *buf;
>>>>>     	u32 len;
>>>>>     	u32 off;
>>>>> +	u32 buf_len;
>>>>>     	bool reply;
>>>>>     };
>>>>> +struct virtio_vsock_buf {
>>>>> +	struct list_head list;
>>>>> +	void *addr;
>>>>> +	u32 len;
>>>>> +	u32 off;
>>>>> +};
>>>>> +
>>>>>     struct virtio_vsock_pkt_info {
>>>>>     	u32 remote_cid, remote_port;
>>>>>     	struct vsock_sock *vsk;
>>>>> diff --git a/net/vmw_vsock/virtio_transport.c
b/net/vmw_vsock/virtio_transport.c
>>>>> index 15eb5d3d4750..af1d2ce12f54 100644
>>>>> --- a/net/vmw_vsock/virtio_transport.c
>>>>> +++ b/net/vmw_vsock/virtio_transport.c
>>>>> @@ -280,6 +280,7 @@ static void virtio_vsock_rx_fill(struct
virtio_vsock *vsock)
>>>>>     			break;
>>>>>     		}
>>>>> +		pkt->buf_len = buf_len;
>>>>>     		pkt->len = buf_len;
>>>>>     		sg_init_one(&hdr, &pkt->hdr,
sizeof(pkt->hdr));
>>>>> diff --git a/net/vmw_vsock/virtio_transport_common.c
b/net/vmw_vsock/virtio_transport_common.c
>>>>> index 602715fc9a75..0248d6808755 100644
>>>>> --- a/net/vmw_vsock/virtio_transport_common.c
>>>>> +++ b/net/vmw_vsock/virtio_transport_common.c
>>>>> @@ -65,6 +65,9 @@ virtio_transport_alloc_pkt(struct
virtio_vsock_pkt_info *info,
>>>>>     		pkt->buf = kmalloc(len, GFP_KERNEL);
>>>>>     		if (!pkt->buf)
>>>>>     			goto out_pkt;
>>>>> +
>>>>> +		pkt->buf_len = len;
>>>>> +
>>>>>     		err = memcpy_from_msg(pkt->buf, info->msg,
len);
>>>>>     		if (err)
>>>>>     			goto out;
>>>>> @@ -86,6 +89,46 @@ virtio_transport_alloc_pkt(struct
virtio_vsock_pkt_info *info,
>>>>>     	return NULL;
>>>>>     }
>>>>> +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.

Thanks

>
>>> Do you suggest to implement something similar, or for now we can
use my
>>> approach and if we will merge the datapath we can reuse the
virtio-net
>>> approach?
>>
>> I think we need a better threshold. If I understand the patch
correctly, we
>> will do copy unless the packet is 64K when guest is doing receiving. 1
byte
>> packet is indeed a problem, but we need to solve it without losing too
much
>> performance.
> It is correct. I'll try to figure out a better threshold and the usage
of
> order 0 page.
>
> Thanks again for your advices,
> Stefano