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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 942C6ECE58C for ; Fri, 11 Oct 2019 13:40:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6DF19214AF for ; Fri, 11 Oct 2019 13:40:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728588AbfJKNky (ORCPT ); Fri, 11 Oct 2019 09:40:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57836 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728546AbfJKNkx (ORCPT ); Fri, 11 Oct 2019 09:40:53 -0400 Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EF796757CC for ; Fri, 11 Oct 2019 13:40:52 +0000 (UTC) Received: by mail-wm1-f69.google.com with SMTP id k9so4140744wmb.0 for ; Fri, 11 Oct 2019 06:40:52 -0700 (PDT) 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=ycjAUNtwkoO5CwuugdxxhPrwcqba9MD0MTVWww0Ry8o=; b=pHWCe/LdFN0lr5Rx0KiwFoS5SVtJuQ4lW5uOvbmHzXv5gIfU9cGz9+2cLzgShyAfYc RRHdK1QjpjJOUOeFfgCha3m6uFZO4U4X6XcpsomszROw3a4EmVGLCxzxaeMSP2kWsimc Hw7kzEjR811sI7HJEP5p+IyTv3Hd1kTV2sRXaenF37CNTObdpyMW2giMshOSiBpdbHUu J+HmNPgVNvNT5MP3iKnLngzfl7XUwoIiLzyGiroVLJ66pDBasjQEkeP97I/l/P6gC4nG r0HvALYgfSB0lTYAnTTWyBu4/Y5hvNjIiAN8Sz0QJH0UdaV9TljQgZNUpqEV1spsTyyL XV+g== X-Gm-Message-State: APjAAAWHZFzw9ol2HLVHRS1STzN0iwtuxcufIdoBmJiygkjNXIrHxcrp 5f0gQM/DhyL15YiDF7JJ6BW6lvWWn/j8Wpsm6iMJEUKzdqbmQPCwrVpWfEvC3bkecpk4wgcXU54 MNe4vIXp17tNw X-Received: by 2002:a7b:c387:: with SMTP id s7mr3114893wmj.110.1570801251576; Fri, 11 Oct 2019 06:40:51 -0700 (PDT) X-Google-Smtp-Source: APXvYqwa2JlipPtOJ7W7B7ExYLkyrReSYaA52mIUw0NmpzMFmVUy7kZcDXl/SyiLE9qQIYJ/Xwp3hg== X-Received: by 2002:a7b:c387:: with SMTP id s7mr3114877wmj.110.1570801251192; Fri, 11 Oct 2019 06:40:51 -0700 (PDT) Received: from steredhat (host174-200-dynamic.52-79-r.retail.telecomitalia.it. [79.52.200.174]) by smtp.gmail.com with ESMTPSA id 59sm17597436wrc.23.2019.10.11.06.40.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Oct 2019 06:40:50 -0700 (PDT) Date: Fri, 11 Oct 2019 15:40:48 +0200 From: Stefano Garzarella To: "Michael S. Tsirkin" Cc: Stefan Hajnoczi , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, "David S. Miller" , virtualization@lists.linux-foundation.org, Jason Wang , kvm Subject: Re: [PATCH v4 1/5] vsock/virtio: limit the memory used per-socket Message-ID: 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: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190901024525-mutt-send-email-mst@kernel.org> User-Agent: NeoMutt/20180716 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Sun, Sep 1, 2019 at 8:56 AM 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). > > > > > > > > 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. > > > > > > > > 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. > > > > > > > > Reviewed-by: Stefan Hajnoczi > > > > Signed-off-by: Stefano Garzarella > > > > > > 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? > > > > > > > Since I'm back from holidays, I'm restarting this thread to figure out > > how to address the issue completely. > > > > 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: > > > > This issue affect only the "host->guest" path. In this case, when the > > 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. > > > > 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 */ > > > > /* remote vars */ > > peer_buf_alloc /* peer's buf_alloc */ > > peer_fwd_cnt /* peer's fwd_cnt */ > > > > 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. > > > > 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. > > > > The local 'buf_alloc' value can be modified by the user space using > > setsockopt() with optname=SO_VM_SOCKETS_BUFFER_SIZE. > > > > Before to send a packet, the peer checks the space available: > > credit_available = peer_buf_alloc - (tx_cnt - peer_fwd_cnt) > > and it will send up to credit_available bytes to the other peer. > > > > 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 negotiated. > > 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 = buf_alloc - bytes_not_used. > > - This should be compatible also with old drivers. > > > > Maybe the second is less invasive, but will it be too tricky? > > Any other advice or suggestions? > > > > Thanks in advance, > > Stefano > > 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. > Hi Michael, sorry for the long silence, but I focused on multi-transport. Before to implement your idea, I tried to do some calculations and looking better to our credit mechanism: buf_alloc = 256 KB (default, tunable through setsockopt) sizeof(struct virtio_vsock_pkt) = 128 - guest (we use preallocated 4 KB buffers to receive packets, copying small packet - < 128 -) worst_case = 129 buf_size = 4 KB credit2mem = (buf_size + sizeof(struct virtio_vsock_pkt)) / worst_case = 32 credit_published = buf_alloc / credit2mem = ~8 KB Space for just 2 full packet (4 KB) - host (we copy packets from the vring, allocating the space for the payload) worst_case = 1 buf_size = 1 credit2mem = (buf_size + sizeof(struct virtio_vsock_pkt)) / worst_case = 129 credit_published = buf_alloc / credit2mem = ~2 KB Less than a full packet (guest now can send up to 64 KB with a single packet, so it will be limited to 2 KB) Current memory consumption in the worst case if the RX queue is full: - guest mem = (buf_alloc / worst_case) * (buf_size + sizeof(struct virtio_vsock_pkt) = ~8MB - host mem = (buf_alloc / worst_case) * (buf_size + sizeof(struct virtio_vsock_pkt) = ~32MB I think that the performance with big packets will be affected, but I still have to try. Another approach that I want to explore is to play with buf_alloc published to the peer. One thing that's not clear to me yet is the meaning of SO_VM_SOCKETS_BUFFER_SIZE: - max amount of memory used in the RX queue - max amount of payload bytes in the RX queue (without overhead of struct virtio_vsock_pkt + preallocated buffer) >From the 'include/uapi/linux/vm_sockets.h': /* Option name for STREAM socket buffer size. Use as the option name in * setsockopt(3) or getsockopt(3) to set or get an unsigned long long that * specifies the size of the buffer underlying a vSockets STREAM socket. * Value is clamped to the MIN and MAX. */ #define SO_VM_SOCKETS_BUFFER_SIZE 0 Regardless, I think we need to limit memory consumption in some way. I'll check the implementation of other transports, to understand better. I'll keep you updated! Thanks, Stefano