[bpf-next,v5,0/8] bpf: Reduce memory usage for bpf_global_percpu_ma

Message

Yonghong Song Dec. 21, 2023, 4:59 a.m. UTC

Currently when a bpf program intends to allocate memory for percpu kptr,
the verifier will call bpf_mem_alloc_init() to prefill all supported
unit sizes and this caused memory consumption very big for large number
of cpus. For example, for 128-cpu system, the total memory consumption
with initial prefill is ~175MB. Things will become worse for systems
with even more cpus.

Patch 1 avoids unnecessary extra percpu memory allocation.
Patch 2 adds objcg to bpf_mem_alloc at init stage so objcg can be
associated with root cgroup and objcg can be passed to later
bpf_mem_alloc_percpu_unit_init().
Patch 3 addresses memory consumption issue by avoiding to prefill
with all unit sizes, i.e. only prefilling with user specified size.
Patch 4 further reduces memory consumption by limiting the
number of prefill entries for percpu memory allocation.
Patch 5 has much smaller low/high watermarks for percpu allocation
to reduce memory consumption.
Patch 6 rejects percpu memory allocation with bpf_global_percpu_ma
when allocation size is greater than 512 bytes.
Patch 7 fixed test_bpf_ma test due to Patch 5.
Patch 8 added one test to show the verification failure log message.

Changelogs:
  v4 -> v5:
    . Do not do bpf_global_percpu_ma initialization at init stage, instead
      doing initialization when the verifier knows it is going to be used
      by bpf prog.
    . Using much smaller low/high watermarks for percpu allocation.
  v3 -> v4:
    . Add objcg to bpf_mem_alloc during init stage.
    . Initialize objcg at init stage but use it in bpf_mem_alloc_percpu_unit_init().
    . Remove check_obj_size() in bpf_mem_alloc_percpu_unit_init().
  v2 -> v3:
    . Clear the bpf_mem_cache if prefill fails.
    . Change test_bpf_ma percpu allocation tests to use bucket_size
      as allocation size instead of bucket_size - 8.
    . Remove __GFP_ZERO flag from __alloc_percpu_gfp() call.
  v1 -> v2:
    . Avoid unnecessary extra percpu memory allocation.
    . Add a separate function to do bpf_global_percpu_ma initialization
    . promote.
    . Promote function static 'sizes' array to file static.
    . Add comments to explain to refill only one item for percpu alloc.

Yonghong Song (8):
  bpf: Avoid unnecessary extra percpu memory allocation
  bpf: Add objcg to bpf_mem_alloc
  bpf: Allow per unit prefill for non-fix-size percpu memory allocator
  bpf: Refill only one percpu element in memalloc
  bpf: Use smaller low/high marks for percpu allocation
  bpf: Limit up to 512 bytes for bpf_global_percpu_ma allocation
  selftests/bpf: Cope with 512 bytes limit with bpf_global_percpu_ma
  selftests/bpf: Add a selftest with > 512-byte percpu allocation size

 include/linux/bpf_mem_alloc.h                 |  8 ++
 kernel/bpf/memalloc.c                         | 98 ++++++++++++++++---
 kernel/bpf/verifier.c                         | 42 +++++---
 .../selftests/bpf/prog_tests/test_bpf_ma.c    | 20 ++--
 .../selftests/bpf/progs/percpu_alloc_fail.c   | 18 ++++
 .../testing/selftests/bpf/progs/test_bpf_ma.c | 66 ++++++-------
 6 files changed, 186 insertions(+), 66 deletions(-)