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Thu, 31 Dec 2020 06:50:50 +0000 Date: Wed, 30 Dec 2020 22:50:44 -0800 From: Martin KaFai Lau To: CC: , , , Subject: Re: [PATCH bpf-next 1/2] bpf: try to avoid kzalloc in cgroup/{s,g}etsockopt Message-ID: <20201231065038.k637ewwyqclq2nxh@kafai-mbp.dhcp.thefacebook.com> References: <20201217172324.2121488-1-sdf@google.com> <20201217172324.2121488-2-sdf@google.com> <20201222191107.bbg6yafayxp4jx5i@kafai-mbp.dhcp.thefacebook.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Originating-IP: [2620:10d:c090:400::5:d5ef] X-ClientProxiedBy: CO2PR04CA0179.namprd04.prod.outlook.com (2603:10b6:104:4::33) To BY5PR15MB3571.namprd15.prod.outlook.com (2603:10b6:a03:1f6::32) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from kafai-mbp.dhcp.thefacebook.com (2620:10d:c090:400::5:d5ef) by CO2PR04CA0179.namprd04.prod.outlook.com (2603:10b6:104:4::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3721.20 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?us-ascii?Q?3qJ23X4q7MHds6/h25qeeYsM+by6mJxbMf7vSfmSb/ELaeif8RLt88LWmK1J?= =?us-ascii?Q?IqsZCFZjJ3dzEdLquy4m4ZTv70C6dGyBgCZ29pzV6QNNZr5NT788/ecfDRC8?= =?us-ascii?Q?etwhpBGLTgYNe7eyS2E8jw4xbgSMXN/khTVoE//6zBqM/WzOcMJU/hQnDlay?= =?us-ascii?Q?T2ZtNKMgoyZVktaaYnERyNJAu26P4CccYIjjwRRTRgkVofQYbLEirGuHk2jF?= =?us-ascii?Q?8qgnqleVp2KYusOAjvoLeEzDrCL3hTfLxXW741O+mDiH3BOAMWjZ4w5J+I2D?= =?us-ascii?Q?tElw+CDDYqjigcGBsRPnymev680EUIMQI6dIPONnURlgGtlgFcgntELoOMaN?= =?us-ascii?Q?pS0CXr5nRfDcP1VQMKunp/IuT0cYxTUhH7XM7Bx1xBph7v3ZNL1VCqpM4+0/?= =?us-ascii?Q?K3M93O10bZ1IzJFeDMQMMN2LunFvMRXv1fDMj7dDpvAifnKIpesSRtoxu5m8?= =?us-ascii?Q?8Tc/3PKUzvam7DndbtgsPS7IuazHHZhHFzf0echTW+m4tUtv48xLgJx8WEkV?= =?us-ascii?Q?+UOIH9mG8wTpEt6QB5DmvVHFE2G2xkOGttf0DBaLZTvG0HzlQLjcv/IwmTY8?= =?us-ascii?Q?d9ZeRGd9EmCzEx2EP3IA35bBlWTATc59+JjqGHmWZ+TITL3n0Uh30h6i94hp?= =?us-ascii?Q?9FcSaFmPfIWcpU41xBda62IOvKbzRo3kL/MRq0JkResTDQVGrMuVALDO3PEB?= =?us-ascii?Q?UdxLA+wS19v57hco9p7fG4KJdGbja50xbOm027toPZsm/oM6L/C7yvKEXJqR?= =?us-ascii?Q?ykyy5NLSKgRq/2kkQKOeZUTpbD9bIAb2y1mhe3XrkjYFq86VjJ2Wnw1zCIYN?= =?us-ascii?Q?9WcmOeDlyommwRyd64kMnU67Ez5W2CYoDAgzY5bOU8tRiKysjYuwfXXrQSA8?= =?us-ascii?Q?ikDgwCSe435Hh+9yDYZK5GNTGhlkDw4YyM+z162Sw38b956jkI4Nc4Cc7X+l?= =?us-ascii?Q?jLQBtTzVBVm7qOJ1VeKVGtig6lfDB8X+Q9/CcYqqbktbvCtg3qcvAlgREXSM?= =?us-ascii?Q?AwpNbIAmK3gpT9mwUkwEBg6CaQ=3D=3D?= X-MS-Exchange-CrossTenant-AuthSource: BY5PR15MB3571.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 31 Dec 2020 06:50:50.4485 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-Network-Message-Id: 4c54ab3a-77b6-42be-887c-08d8ad586924 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 7XXP4JgcmB7K/Gjo42LzofxNQAYimVaoGd8BL3q/XhHhFmkSF8DIMQeNN8Bmqej6 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2488 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2020-12-31_02:2020-12-30,2020-12-31 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 bulkscore=0 phishscore=0 mlxlogscore=999 adultscore=0 malwarescore=0 impostorscore=0 suspectscore=0 spamscore=0 clxscore=1015 priorityscore=1501 lowpriorityscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012310036 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Dec 22, 2020 at 07:09:33PM -0800, sdf@google.com wrote: > On 12/22, Martin KaFai Lau wrote: > > On Thu, Dec 17, 2020 at 09:23:23AM -0800, Stanislav Fomichev wrote: > > > When we attach a bpf program to cgroup/getsockopt any other getsockopt() > > > syscall starts incurring kzalloc/kfree cost. While, in general, it's > > > not an issue, sometimes it is, like in the case of TCP_ZEROCOPY_RECEIVE. > > > TCP_ZEROCOPY_RECEIVE (ab)uses getsockopt system call to implement > > > fastpath for incoming TCP, we don't want to have extra allocations in > > > there. > > > > > > Let add a small buffer on the stack and use it for small (majority) > > > {s,g}etsockopt values. I've started with 128 bytes to cover > > > the options we care about (TCP_ZEROCOPY_RECEIVE which is 32 bytes > > > currently, with some planned extension to 64 + some headroom > > > for the future). > > > > > > It seems natural to do the same for setsockopt, but it's a bit more > > > involved when the BPF program modifies the data (where we have to > > > kmalloc). The assumption is that for the majority of setsockopt > > > calls (which are doing pure BPF options or apply policy) this > > > will bring some benefit as well. > > > > > > Signed-off-by: Stanislav Fomichev > > > --- > > > include/linux/filter.h | 3 +++ > > > kernel/bpf/cgroup.c | 41 +++++++++++++++++++++++++++++++++++++++-- > > > 2 files changed, 42 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/linux/filter.h b/include/linux/filter.h > > > index 29c27656165b..362eb0d7af5d 100644 > > > --- a/include/linux/filter.h > > > +++ b/include/linux/filter.h > > > @@ -1281,6 +1281,8 @@ struct bpf_sysctl_kern { > > > u64 tmp_reg; > > > }; > > > > > > +#define BPF_SOCKOPT_KERN_BUF_SIZE 128 > > Since these 128 bytes (which then needs to be zero-ed) is modeled after > > the TCP_ZEROCOPY_RECEIVE use case, it will be useful to explain > > a use case on how the bpf prog will interact with > > getsockopt(TCP_ZEROCOPY_RECEIVE). > The only thing I would expect BPF program can do is to return EPERM > to cause application to fallback to non-zerocopy path (and, mostly, > bypass). I don't think BPF can meaningfully mangle the data in struct > tcp_zerocopy_receive. > > Does it address your concern? Or do you want me to add a comment or > something? I was asking because, while 128 byte may work best for TCP_ZEROCOPY_RECEIVCE, it is many unnecessary byte-zeroings for most options though. Hence, I am interested to see if there is a practical bpf use case for TCP_ZEROCOPY_RECEIVE.