netdev - [RFC PATCH bpf-next v2 0/2] bpf: adding map batch processing support

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Date:   Fri, 6 Sep 2019 15:54:32 -0700
From:   Yonghong Song <yhs@...com>
To:     <ast@...com>, <daniel@...earbox.net>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
CC:     <kernel-team@...com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Brian Vazquez <brianvv@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>
Subject: [RFC PATCH bpf-next v2 0/2] bpf: adding map batch processing support

Previous discussion at:
  https://lore.kernel.org/bpf/7ba9b492-8a08-a1d0-9c6e-03be4b8e5e07@fb.com/T/#t

Previous approach tries to use existing per-map looks like
bpf_map_{get_next_key, lookup_elem, update_elem, delete_elem}
to implement a batching process.

It has a series drawback when the prev_key used by bpf_map_get_next_key()
is not in hash table. In that case, as the hash table has no idea where
the `prev_key` has been placed in the bucket before deletion, currently,
it returns the first key. This makes batch processing may see
duplicated elements, or in worst case if the hash table has heavy
update/delete, the batch processing may never finish.

This RFC patch set implements bucket based batching for hashtab.
That is, for lookup/delete, either the whole bucket is processed
or none of elements in the bucket is processed. Forward progress
is also guaranteed as long as user provides enough buffer.

This RFC also serves as a base for discussion at upcoming
LPC2019 BPF Microconference.

Changelogs:
   v1 -> RFC v2:
     . To address the bpf_map_get_next_key() issue where
       if a key is not available the first key will be returned,
       implement per-map batch operations for hashtab/lru_hashtab,
       using bucket lock, as suggested by Alexei.

Cc: Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc: Brian Vazquez <brianvv@...gle.com>
Cc: Stanislav Fomichev <sdf@...gle.com>

Yonghong Song (2):
  bpf: adding map batch processing support
  tools/bpf: test bpf_map_lookup_and_delete_batch()

 include/linux/bpf.h                           |   9 +
 include/uapi/linux/bpf.h                      |  22 ++
 kernel/bpf/hashtab.c                          | 324 ++++++++++++++++++
 kernel/bpf/syscall.c                          |  68 ++++
 tools/include/uapi/linux/bpf.h                |  22 ++
 tools/lib/bpf/bpf.c                           |  59 ++++
 tools/lib/bpf/bpf.h                           |  13 +
 tools/lib/bpf/libbpf.map                      |   4 +
 .../map_tests/map_lookup_and_delete_batch.c   | 155 +++++++++
 9 files changed, 676 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/map_tests/map_lookup_and_delete_batch.c

-- 
2.17.1