netdev - Re: [PATCH v4 1/5] vsock/virtio: limit the memory used per-socket

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Date:   Mon, 2 Sep 2019 10:55:02 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...il.com>
Cc:     kvm@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v4 1/5] vsock/virtio: limit the memory used per-socket

On Mon, Sep 02, 2019 at 09:39:12AM +0100, Stefan Hajnoczi wrote:
> On Sun, Sep 01, 2019 at 02:56:44AM -0400, Michael S. Tsirkin wrote:
> > 
> > OK let me try to clarify.  The idea is this:
> > 
> > Let's say we queue a buffer of 4K, and we copy if len < 128 bytes.  This
> > means that in the worst case (128 byte packets), each byte of credit in
> > the socket uses up 4K/128 = 16 bytes of kernel memory. In fact we need
> > to also account for the virtio_vsock_pkt since I think it's kept around
> > until userspace consumes it.
> > 
> > Thus given X buf alloc allowed in the socket, we should publish X/16
> > credits to the other side. This will ensure the other side does not send
> > more than X/16 bytes for a given socket and thus we won't need to
> > allocate more than X bytes to hold the data.
> > 
> > We can play with the copy break value to tweak this.

Thanks Michael, now it is perfectly clear. It seems an excellent solution and
easy to implement. I'll work on that.

> 
> This seems like a reasonable solution.  Hopefully the benchmark results
> will come out okay too.

Yes, as Michael suggested I'll play with the copy break value to see as
benchmark has affected.

Thank you very much,
Stefano