Re: [PATCH bpf-next v2 0/3] Allow struct_ops maps with a large number of programs

[Kui-Feng Lee <sinquersw@gmail.com>]

On 2/21/24 14:59, thinker.li@gmail.com wrote:
> From: Kui-Feng Lee <thinker.li@gmail.com>
> 
> The BPF struct_ops previously only allowed for one page to be used for
> the trampolines of all links in a map. However, we have recently run
> out of space due to the large number of BPF program links. By
> allocating additional pages when we exhaust an existing page, we can
> accommodate more links in a single map.
> 
> The variable st_map->image has been changed to st_map->image_pages,
> and its type has been changed to an array of pointers to buffers of
> PAGE_SIZE. The array is dynamically resized and additional pages are
> allocated when all existing pages are exhausted.

Sorry for not updating this part about resizing. The array is not
resized anymore. But, additional pages are allocated.

> 
> The test case loads a struct_ops maps having 40 programs. Their
> trampolines takes about 6.6k+ bytes over 1.5 pages on x86.
> 
> Kui-Feng Lee (3):
>    bpf, net: validate struct_ops when updating value.
>    bpf: struct_ops supports more than one page for trampolines.
>    selftests/bpf: Test struct_ops maps with a large number of program
>      links.
> 
>   kernel/bpf/bpf_struct_ops.c                   | 123 ++++++++++++------
>   net/ipv4/tcp_cong.c                           |   6 +-
>   .../selftests/bpf/bpf_testmod/bpf_testmod.h   |  44 +++++++
>   .../prog_tests/test_struct_ops_multi_pages.c  |  31 +++++
>   .../bpf/progs/struct_ops_multi_pages.c        | 102 +++++++++++++++
>   5 files changed, 263 insertions(+), 43 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_multi_pages.c
>   create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_multi_pages.c
>