From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58F10C3A59B for ; Mon, 2 Sep 2019 08:39:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 28EDC22CF7 for ; Mon, 2 Sep 2019 08:39:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="JE+rTGDd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730697AbfIBIjS (ORCPT ); Mon, 2 Sep 2019 04:39:18 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:38479 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729870AbfIBIjQ (ORCPT ); Mon, 2 Sep 2019 04:39:16 -0400 Received: by mail-wr1-f67.google.com with SMTP id l11so4263623wrx.5; Mon, 02 Sep 2019 01:39:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=84tNa0LJ5qNP8ceq2AHt9GMRkk+XoKF4Wbr0EYQvIpE=; b=JE+rTGDd3vfb9wVcnjiTAQ6VJuKqNZw1kp4lvjPYJQleCdZutoksvcSMrlbLlijgCD eA0G7FMldjru0uK1XH4l74xGOPEmK3pJ1sPHZkOIrZr4BS6wnRxvwBqRoz9XiIQerESa jX+iX5JReRbNpB+qIm2TIK6sWuVMsKA0S0XMYbWYNcj2+SuMNh2YzUcPN3Ivu6DSSW3b rT05eDiPQfsvIDsgAW75tfQ1C52HqBA7opRcNIzA1Vmi/6sQ/3QfMZ+3+lgjZDe3fbDE oOkXpLo2mcwKwq9a0L+APjev3rJXds2O1xredJzBH0qz936K/dnrmcjHVT3Q0ByGdP97 xxgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=84tNa0LJ5qNP8ceq2AHt9GMRkk+XoKF4Wbr0EYQvIpE=; b=FYWDRnhcv8JMIpaGwtRaGbDlr553sJ5NDhPk7C7p0BWT89JtVuqWzqiGEdFBKBvfjh 7mV84UEFxqR99nNWFk2e/CsSHWAMq8gdrd3K8zkFUfzuywC1zbd71pYeqyYD7rurTmkv bLXhWlKQBvqEBq0j4aDWzuXZLqwGY+Dgn4F7/H+ZeXii17ZG0AabURdUPlo4IhJ/yy5c DCNrSEPtkcPdhFnEwI7DXJuUaOK1KJhZEviolenb/n+MDWrbScqO3wb03wYgpHA1LtIT 35iO+Vq4QDGQ/KoMpPBciiNRudLmEquKJuffXLbLuO2Eqvq/fw9ygtODSej8WX4ACzSW nalA== X-Gm-Message-State: APjAAAUa3TR6P6WNRmjlMyBi0uV8bk5q+4AGELDARMO4QbZbJCOGC1ll D1BiLc86foYVMuOkxvxdRVE= X-Google-Smtp-Source: APXvYqw8kmUFZTdml86OFk4ExnbC4on8hvb43jeEB+SHfHs0C2+GnjIN7wyw+xxJ23zIcyfbPlXgSw== X-Received: by 2002:a5d:6a45:: with SMTP id t5mr33771273wrw.228.1567413555153; Mon, 02 Sep 2019 01:39:15 -0700 (PDT) Received: from localhost ([51.15.41.238]) by smtp.gmail.com with ESMTPSA id b18sm17854812wro.34.2019.09.02.01.39.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Sep 2019 01:39:14 -0700 (PDT) Date: Mon, 2 Sep 2019 09:39:12 +0100 From: Stefan Hajnoczi To: "Michael S. Tsirkin" Cc: Stefano Garzarella , kvm@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Stefan Hajnoczi , "David S. Miller" Subject: Re: [PATCH v4 1/5] vsock/virtio: limit the memory used per-socket Message-ID: <20190902083912.GA9069@stefanha-x1.localdomain> References: <20190717113030.163499-1-sgarzare@redhat.com> <20190717113030.163499-2-sgarzare@redhat.com> <20190729095956-mutt-send-email-mst@kernel.org> <20190830094059.c7qo5cxrp2nkrncd@steredhat> <20190901024525-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="gKMricLos+KVdGMg" Content-Disposition: inline In-Reply-To: <20190901024525-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org --gKMricLos+KVdGMg Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Sep 01, 2019 at 02:56:44AM -0400, Michael S. Tsirkin wrote: > On Fri, Aug 30, 2019 at 11:40:59AM +0200, Stefano Garzarella wrote: > > On Mon, Jul 29, 2019 at 10:04:29AM -0400, Michael S. Tsirkin wrote: > > > On Wed, Jul 17, 2019 at 01:30:26PM +0200, 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. These buffers are preallocated by the guest > > > > with a fixed size (4 KB). > > > >=20 > > > > 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 other sockets. > > > >=20 > > > > This patch mitigates this issue copying the payload of small > > > > packets (< 128 bytes) into the buffer of last packet queued, in > > > > order to avoid wasting memory. > > > >=20 > > > > Reviewed-by: Stefan Hajnoczi > > > > Signed-off-by: Stefano Garzarella > > >=20 > > > This is good enough for net-next, but for net I think we > > > should figure out how to address the issue completely. > > > Can we make the accounting precise? What happens to > > > performance if we do? > > >=20 > >=20 > > Since I'm back from holidays, I'm restarting this thread to figure out > > how to address the issue completely. > >=20 > > I did a better analysis of the credit mechanism that we implemented in > > virtio-vsock to get a clearer view and I'd share it with you: > >=20 > > This issue affect only the "host->guest" path. In this case, when t= he > > host wants to send a packet to the guest, it uses a "free" buffer > > allocated by the guest (4KB). > > The "free" buffers available for the host are shared between all > > sockets, instead, the credit mechanism is per-socket, I think to > > avoid the starvation of others sockets. > > The guests re-fill the "free" queue when the available buffers are > > less than half. > >=20 > > Each peer have these variables in the per-socket state: > > /* local vars */ > > buf_alloc /* max bytes usable by this socket > > [exposed to the other peer] */ > > fwd_cnt /* increased when RX packet is consumed by the > > user space [exposed to the other peer] */ > > tx_cnt /* increased when TX packet is sent to the other= peer */ > >=20 > > /* remote vars */ > > peer_buf_alloc /* peer's buf_alloc */ > > peer_fwd_cnt /* peer's fwd_cnt */ > >=20 > > When a peer sends a packet, it increases the 'tx_cnt'; when the > > receiver consumes the packet (copy it to the user-space buffer), it > > increases the 'fwd_cnt'. > > Note: increments are made considering the payload length and not the > > buffer length. > >=20 > > The value of 'buf_alloc' and 'fwd_cnt' are sent to the other peer in > > all packet headers or with an explicit CREDIT_UPDATE packet. > >=20 > > The local 'buf_alloc' value can be modified by the user space using > > setsockopt() with optname=3DSO_VM_SOCKETS_BUFFER_SIZE. > >=20 > > Before to send a packet, the peer checks the space available: > > credit_available =3D peer_buf_alloc - (tx_cnt - peer_fwd_cnt) > > and it will send up to credit_available bytes to the other peer. > >=20 > > Possible solutions considering Michael's advice: > > 1. Use the buffer length instead of the payload length when we increment > > the counters: > > - This approach will account precisely the memory used per socket. > > - This requires changes in both guest and host. > > - It is not compatible with old drivers, so a feature should be negot= iated. > > 2. Decrease the advertised 'buf_alloc' taking count of bytes queued in > > the socket queue but not used. (e.g. 256 byte used on 4K available in > > the buffer) > > - pkt->hdr.buf_alloc =3D buf_alloc - bytes_not_used. > > - This should be compatible also with old drivers. > >=20 > > Maybe the second is less invasive, but will it be too tricky? > > Any other advice or suggestions? > >=20 > > Thanks in advance, > > Stefano >=20 > OK let me try to clarify. The idea is this: >=20 > 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 =3D 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. >=20 > 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. >=20 > We can play with the copy break value to tweak this. This seems like a reasonable solution. Hopefully the benchmark results will come out okay too. Stefan --gKMricLos+KVdGMg Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl1s1TAACgkQnKSrs4Gr c8gLsQf/X+M+3+I6vdXaOQqa3p6XuU6eKcoPYS3AZKsgf2/Hu7lfjlaFu1me49Qx eoM5VhsaVIzCfF7TJgUthcFsoG+nAc1sc+TPm16rBnDArLUHGMrny6LTZHGmkvi2 HxnjGjLD/1CNxeeyL3HDyyzkKtG32surnGULXLKqW/599PQxHDq+QXSWysC8QTX7 MKE3vc7zIpRh7PiXbPdh4IH8UUeHdEbdYrRoaK0uiXN47vUFOUdM1t8iMG1u/C8t 8X3f/wnHGl7Z6k+QH/3SMme3xihN0/F/TQW8PqyZdUMB7I+X5URicB4ECRpQ3dgE c0cux2rhFpAIui9MpqD7+fagnhksmw== =wVO3 -----END PGP SIGNATURE----- --gKMricLos+KVdGMg--