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docs: bpf: map_array: Specify BPF_MAP_TYPE_PERCPU_ARRAY value size limit 

Specify value size limit for BPF_MAP_TYPE_PERCPU_ARRAY which
is PCPU_MIN_UNIT_SIZE (32 kb). In percpu allocator (mm: percpu),
any request with a size greater than PCPU_MIN_UNIT_SIZE is rejected.

Signed-off-by: Alex Tran <alex.t.tran@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20251115063531.2302903-1-alex.t.tran@gmail.com
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Alex Tran 2025-11-14 22:35:31 -08:00 committed by Andrii Nakryiko
parent 590699d858
commit 44bf461182
1 changed files with 3 additions and 2 deletions
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Documentation/bpf/map_array.rst
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@ -15,8 +15,9 @@ of constant size. The size of the array is defined in ``max_entries`` at
creation time. All array elements are pre-allocated and zero initialized when
created. ``BPF_MAP_TYPE_PERCPU_ARRAY`` uses a different memory region for each
CPU whereas ``BPF_MAP_TYPE_ARRAY`` uses the same memory region. The value
stored can be of any size, however, all array elements are aligned to 8
bytes.
stored can be of any size for ``BPF_MAP_TYPE_ARRAY`` and not more than
``PCPU_MIN_UNIT_SIZE`` (32 kB) for ``BPF_MAP_TYPE_PERCPU_ARRAY``. All
array elements are aligned to 8 bytes.
Since kernel 5.5, memory mapping may be enabled for ``BPF_MAP_TYPE_ARRAY`` by
setting the flag ``BPF_F_MMAPABLE``. The map definition is page-aligned and