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=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 81339C433ED for ; Thu, 1 Apr 2021 07:18:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3813661057 for ; Thu, 1 Apr 2021 07:18:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233450AbhDAHOx (ORCPT ); Thu, 1 Apr 2021 03:14:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:49564 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233223AbhDAHOe (ORCPT ); Thu, 1 Apr 2021 03:14:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617261272; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7TEwuO+P7X/6uf2GVYnj6OAUGebvJaBspYwyuLPZGkY=; b=ECyTSwM2qmzdUY+B/fXTu1GbvzJLIvAJTXby0aovbCtUgjcGbv9S4V1XVs1VmlqXgazehN Zs0t7cgSne2DYLWxrxsa9X3Al5KFp6IqxfOt0d/Oukz85NtvCK7t1EvycwdxA0Bxw3vSim YsdTiM7kNHZxkVeMg1oFe+h1rQAax1Q= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-36-PGhyU7pUOKq15XGHDake2w-1; Thu, 01 Apr 2021 03:14:28 -0400 X-MC-Unique: PGhyU7pUOKq15XGHDake2w-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 78ED2807331; Thu, 1 Apr 2021 07:14:27 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-210.pek2.redhat.com [10.72.13.210]) by smtp.corp.redhat.com (Postfix) with ESMTP id E0A4D19C44; Thu, 1 Apr 2021 07:14:19 +0000 (UTC) Subject: Re: [PATCH net] net: avoid 32 x truesize under-estimation for tiny skbs To: "Michael S. Tsirkin" , Eric Dumazet Cc: Xuan Zhuo , Eric Dumazet , netdev , Alexander Duyck , Paolo Abeni , Greg Thelen , "David S . Miller" , Jakub Kicinski , su-lifan@linux.alibaba.com, "dust.li" References: <20210113161819.1155526-1-eric.dumazet@gmail.com> <1617007696.5731978-1-xuanzhuo@linux.alibaba.com> <20210331040405-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Thu, 1 Apr 2021 15:14:18 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <20210331040405-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org ÔÚ 2021/3/31 ÏÂÎç4:11, Michael S. Tsirkin дµÀ: > On Mon, Mar 29, 2021 at 11:06:09AM +0200, Eric Dumazet wrote: >> On Mon, Mar 29, 2021 at 10:52 AM Xuan Zhuo wrote: >>> On Wed, 13 Jan 2021 08:18:19 -0800, Eric Dumazet wrote: >>>> From: Eric Dumazet >>>> >>>> Both virtio net and napi_get_frags() allocate skbs >>>> with a very small skb->head >>>> >>>> While using page fragments instead of a kmalloc backed skb->head might give >>>> a small performance improvement in some cases, there is a huge risk of >>>> under estimating memory usage. >>>> >>>> For both GOOD_COPY_LEN and GRO_MAX_HEAD, we can fit at least 32 allocations >>>> per page (order-3 page in x86), or even 64 on PowerPC >>>> >>>> We have been tracking OOM issues on GKE hosts hitting tcp_mem limits >>>> but consuming far more memory for TCP buffers than instructed in tcp_mem[2] >>>> >>>> Even if we force napi_alloc_skb() to only use order-0 pages, the issue >>>> would still be there on arches with PAGE_SIZE >= 32768 >>>> >>>> This patch makes sure that small skb head are kmalloc backed, so that >>>> other objects in the slab page can be reused instead of being held as long >>>> as skbs are sitting in socket queues. >>>> >>>> Note that we might in the future use the sk_buff napi cache, >>>> instead of going through a more expensive __alloc_skb() >>>> >>>> Another idea would be to use separate page sizes depending >>>> on the allocated length (to never have more than 4 frags per page) >>>> >>>> I would like to thank Greg Thelen for his precious help on this matter, >>>> analysing crash dumps is always a time consuming task. >>> >>> This patch causes a performance degradation of about 10% in the scenario of >>> virtio-net + GRO. >>> >>> For GRO, there is no way to merge skbs based on frags with this patch, only >>> frag_list can be used to link skbs. The problem that this cause are that compared >>> to the GRO package merged into the frags way, the current skb needs to call >>> kfree_skb_list to release each skb, resulting in performance degradation. >>> >>> virtio-net will store some data onto the linear space after receiving it. In >>> addition to the header, there are also some payloads, so "headlen <= offset" >>> fails. And skb->head_frag is failing when use kmalloc() for skb->head allocation. >>> >> Thanks for the report. >> >> There is no way we can make things both fast for existing strategies >> used by _insert_your_driver >> and malicious usages of data that can sit for seconds/minutes in socket queues. >> >> I think that if you want to gain this 10% back, you have to change >> virtio_net to meet optimal behavior. >> >> Normal drivers make sure to not pull payload in skb->head, only headers. > Hmm we do have hdr_len field, but seem to ignore it on RX. > Jason do you see any issues with using it for the head len? This might work only if the device sets a correct hdr_len. I'm not sure all of the devices can do this properly. E.g for tap, we use skb_headlen() in virtio_net_hdr_from_skb() which depends highly on the behaviour of the underlayer layers (device driver or GRO). And we only set this hint for GSO packet but virtio-net may tries to do GRO for non GSO packets. Thanks > > >> Optimal GRO packets are when payload is in page fragments. >> >> (I am speaking not only for raw performance, but ability for systems >> to cope with network outages and sudden increase of memory usage in >> out of order queues) >> >> This has been quite clearly stated in my changelog. >> >> Thanks. >> >> >>> int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) >>> { >>> struct skb_shared_info *pinfo, *skbinfo = skb_shinfo(skb); >>> unsigned int offset = skb_gro_offset(skb); >>> unsigned int headlen = skb_headlen(skb); >>> >>> ....... >>> >>> if (headlen <= offset) { // virtio-net will fail >>> ........ // merge by frags >>> goto done; >>> } else if (skb->head_frag) { // skb->head_frag is fail when use kmalloc() for skb->head allocation >>> ........ // merge by frags >>> goto done; >>> } >>> >>> merge: >>> ...... >>> >>> if (NAPI_GRO_CB(p)->last == p) >>> skb_shinfo(p)->frag_list = skb; >>> else >>> NAPI_GRO_CB(p)->last->next = skb; >>> >>> ...... >>> return 0; >>> } >>> >>> >>> test cmd: >>> for i in $(seq 1 4) >>> do >>> redis-benchmark -r 10000000 -n 10000000 -t set -d 1024 -c 8 -P 32 -h -p 6379 2>&1 | grep 'per second' & >>> done >>> >>> Reported-by: su-lifan@linux.alibaba.com >>> >>>> Fixes: fd11a83dd363 ("net: Pull out core bits of __netdev_alloc_skb and add __napi_alloc_skb") >>>> Signed-off-by: Eric Dumazet >>>> Cc: Alexander Duyck >>>> Cc: Paolo Abeni >>>> Cc: Michael S. Tsirkin >>>> Cc: Greg Thelen >>>> --- >>>> net/core/skbuff.c | 9 +++++++-- >>>> 1 file changed, 7 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c >>>> index 7626a33cce590e530f36167bd096026916131897..3a8f55a43e6964344df464a27b9b1faa0eb804f3 100644 >>>> --- a/net/core/skbuff.c >>>> +++ b/net/core/skbuff.c >>>> @@ -501,13 +501,17 @@ EXPORT_SYMBOL(__netdev_alloc_skb); >>>> struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len, >>>> gfp_t gfp_mask) >>>> { >>>> - struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache); >>>> + struct napi_alloc_cache *nc; >>>> struct sk_buff *skb; >>>> void *data; >>>> >>>> len += NET_SKB_PAD + NET_IP_ALIGN; >>>> >>>> - if ((len > SKB_WITH_OVERHEAD(PAGE_SIZE)) || >>>> + /* If requested length is either too small or too big, >>>> + * we use kmalloc() for skb->head allocation. >>>> + */ >>>> + if (len <= SKB_WITH_OVERHEAD(1024) || >>>> + len > SKB_WITH_OVERHEAD(PAGE_SIZE) || >>>> (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) { >>>> skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE); >>>> if (!skb) >>>> @@ -515,6 +519,7 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len, >>>> goto skb_success; >>>> } >>>> >>>> + nc = this_cpu_ptr(&napi_alloc_cache); >>>> len += SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); >>>> len = SKB_DATA_ALIGN(len); >>>> >>>> -- >>>> 2.30.0.284.gd98b1dd5eaa7-goog >>>>