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Wed, 18 Nov 2020 01:28:47 +0000 Date: Tue, 17 Nov 2020 17:28:41 -0800 From: Roman Gushchin To: Alexei Starovoitov CC: Daniel Borkmann , bpf , Alexei Starovoitov , Network Development , Andrii Nakryiko , Andrew Morton , linux-mm , LKML , Kernel Team Subject: Re: [PATCH bpf-next v6 06/34] bpf: prepare for memcg-based memory accounting for bpf maps Message-ID: <20201118012841.GA186396@carbon.dhcp.thefacebook.com> References: <20201117034108.1186569-1-guro@fb.com> <20201117034108.1186569-7-guro@fb.com> <41eb5e5b-e651-4cb3-a6ea-9ff6b8aa41fb@iogearbox.net> <20201118004634.GA179309@carbon.dhcp.thefacebook.com> <20201118010703.GC156448@carbon.DHCP.thefacebook.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Originating-IP: [2620:10d:c090:400::5:57cc] X-ClientProxiedBy: CO2PR04CA0105.namprd04.prod.outlook.com (2603:10b6:104:6::31) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.dhcp.thefacebook.com (2620:10d:c090:400::5:57cc) by CO2PR04CA0105.namprd04.prod.outlook.com (2603:10b6:104:6::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3589.20 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 6EiUJG/lZBOTfBoWDjh346eCpJKbZkSfxUvahGOmhEnDTLtPwNxv7xRcqEs055xM+xGFnUhRN95rKhk0qAKb4++fuH+Zy94EWz5fB27kH9lXV/yr5Gq7/jexzMi2RpexnI6NU4dA9WJo7FyicEp/Uektimjn4BSIO8QWYqcZaVEi2BXazK/o7O6/neK9/pAr0BdAkn8rjJvbNnqktVjgEQer7NVEpMAXr5OqPoDs2blkz70yPMpHqb4hX4q855+rm8nhQNwB+/TmppB7oK/c3/Oaw8SLonC2ToYViGVc++LmskGk73HTC33zMMer4uUGFsxNF/PEeH9m6JL7I9hjkffwTz+8x3UqYvFOY9u7Ot8dd6CyMUoA5Fh9O63SFA3QaNwQ0cV8huEvvqEBxrXuMV2cgBOLka3oHpHXO6Uadb/BYVyhKGmCLns2UfqCK9dpWCeHAqoHWGzrIRsgrfEM/67EGrGSsRVrE1sVZxogwxZlnVqcd+rw/pKeuXDMI9SFhPF2Wdu90AoCmihC8nRbInPRFhTMLdITIGSqSUD3Q2cp/ltD9Oqwa5hrUpDRr1ffr4Ix00PUK5wp41gO8u5Ix9nG34EAW6e7VJrceSRIffYg//yKrBZEyXhALiIo/eyZs87i4vZGRQxt7BNX5b+YUrTfYf++5r7lfT65irJluyM= X-MS-Exchange-CrossTenant-Network-Message-Id: 51afb830-d163-49ef-9be4-08d88b614ba2 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Nov 2020 01:28:47.2130 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: NLhfRPv+aJmRyPEYk4lgylhY8LGecA4Gv55OZvUma6NgUq3o9QZAXVHPkY5ChmFy X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR15MB3603 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312,18.0.737 definitions=2020-11-17_15:2020-11-17,2020-11-17 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 bulkscore=0 mlxlogscore=999 mlxscore=0 adultscore=0 spamscore=0 malwarescore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 suspectscore=1 priorityscore=1501 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011180006 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 17, 2020 at 05:11:00PM -0800, Alexei Starovoitov wrote: > On Tue, Nov 17, 2020 at 5:07 PM Roman Gushchin wrote: > > > > On Tue, Nov 17, 2020 at 04:46:34PM -0800, Roman Gushchin wrote: > > > On Wed, Nov 18, 2020 at 01:06:17AM +0100, Daniel Borkmann wrote: > > > > On 11/17/20 4:40 AM, Roman Gushchin wrote: > > > > > In the absolute majority of cases if a process is making a kernel > > > > > allocation, it's memory cgroup is getting charged. > > > > > > > > > > Bpf maps can be updated from an interrupt context and in such > > > > > case there is no process which can be charged. It makes the memory > > > > > accounting of bpf maps non-trivial. > > > > > > > > > > Fortunately, after commit 4127c6504f25 ("mm: kmem: enable kernel > > > > > memcg accounting from interrupt contexts") and b87d8cefe43c > > > > > ("mm, memcg: rework remote charging API to support nesting") > > > > > it's finally possible. > > > > > > > > > > To do it, a pointer to the memory cgroup of the process which created > > > > > the map is saved, and this cgroup is getting charged for all > > > > > allocations made from an interrupt context. > > > > > > > > > > Allocations made from a process context will be accounted in a usual way. > > > > > > > > > > Signed-off-by: Roman Gushchin > > > > > Acked-by: Song Liu > > > > [...] > > > > > +#ifdef CONFIG_MEMCG_KMEM > > > > > +static __always_inline int __bpf_map_update_elem(struct bpf_map *map, void *key, > > > > > + void *value, u64 flags) > > > > > +{ > > > > > + struct mem_cgroup *old_memcg; > > > > > + bool in_interrupt; > > > > > + int ret; > > > > > + > > > > > + /* > > > > > + * If update from an interrupt context results in a memory allocation, > > > > > + * the memory cgroup to charge can't be determined from the context > > > > > + * of the current task. Instead, we charge the memory cgroup, which > > > > > + * contained a process created the map. > > > > > + */ > > > > > + in_interrupt = in_interrupt(); > > > > > + if (in_interrupt) > > > > > + old_memcg = set_active_memcg(map->memcg); > > > > > + > > > > > + ret = map->ops->map_update_elem(map, key, value, flags); > > > > > + > > > > > + if (in_interrupt) > > > > > + set_active_memcg(old_memcg); > > > > > + > > > > > + return ret; > > > > > > > > Hmm, this approach here won't work, see also commit 09772d92cd5a ("bpf: avoid > > > > retpoline for lookup/update/delete calls on maps") which removes the indirect > > > > call, so the __bpf_map_update_elem() and therefore the set_active_memcg() is > > > > not invoked for the vast majority of cases. > > > > > > I see. Well, the first option is to move these calls into map-specific update > > > functions, but the list is relatively long: > > > nsim_map_update_elem() > > > cgroup_storage_update_elem() > > > htab_map_update_elem() > > > htab_percpu_map_update_elem() > > > dev_map_update_elem() > > > dev_map_hash_update_elem() > > > trie_update_elem() > > > cpu_map_update_elem() > > > bpf_pid_task_storage_update_elem() > > > bpf_fd_inode_storage_update_elem() > > > bpf_fd_sk_storage_update_elem() > > > sock_map_update_elem() > > > xsk_map_update_elem() > > > > > > Alternatively, we can set the active memcg for the whole duration of bpf > > > execution. It's simpler, but will add some overhead. Maybe we can somehow > > > mark programs calling into update helpers and skip all others? > > > > Actually, this is problematic if a program updates several maps, because > > in theory they can belong to different cgroups. > > So it seems that the first option is the way to go. Do you agree? > > May be instead of kmalloc_node() that is used by most of the map updates > introduce bpf_map_kmalloc_node() that takes a map pointer as an argument? > And do set_memcg inside? I suspect it's not only kmalloc_node(), but if there will be 2-3 allocation helpers, it sounds like a good idea to me! I'll try and get back with v7 soon. Thanks!