Re: [PATCH v2 bpf-next 0/7] bpf_prog_pack allocator

On Fri, Dec 17, 2021 at 9:13 AM Song Liu [off-list ref] wrote:

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On Dec 17, 2021, at 8:43 AM, Andrii Nakryiko [off-list ref] wrote:

On Fri, Dec 17, 2021 at 8:42 AM Andrii Nakryiko
[off-list ref] wrote:

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On Thu, Dec 16, 2021 at 5:53 PM Song Liu [off-list ref] wrote:

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On Dec 16, 2021, at 12:06 PM, Andrii Nakryiko [off-list ref] wrote:

On Tue, Dec 14, 2021 at 10:01 PM Song Liu [off-list ref] wrote:

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Changes v1 => v2:
1. Use text_poke instead of writing through linear mapping. (Peter)
2. Avoid making changes to non-x86_64 code.

Most BPF programs are small, but they consume a page each. For systems
with busy traffic and many BPF programs, this could also add significant
pressure to instruction TLB.

This set tries to solve this problem with customized allocator that pack
multiple programs into a huge page.

Patches 1-5 prepare the work. Patch 6 contains key logic of the allocator.
Patch 7 uses this allocator in x86_64 jit compiler.

There are test failures, please see [0]. But I was also wondering if
there could be an explicit selftest added to validate that all this
huge page machinery is actually activated and working as expected?

We can enable some debug option that dumps the page table. Then from the
page table, we can confirm the programs are running on a huge page. This
only works on x86_64 though. WDYT?

I don't know what exactly is involved, so it's hard to say. Ideally
whatever we do doesn't complicate our CI setup. Can we use BPF tracing
magic to check this from inside the kernel somehow?

But I don't feel strongly about this, if it's hard to detect, it's
fine to not have a specific test (especially that it's very
architecture-specific)

It will be more or less architecture-specific, as we need somehow walk
the page table (with debug option or with BPF iterator). I will try
something.

If BPF iterator approach works, that would be great!

Thanks,
Song

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Thanks,
Song

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[0] https://github.com/kernel-patches/bpf/runs/4530372387?check_suite_focus=true

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Song Liu (7):
x86/Kconfig: select HAVE_ARCH_HUGE_VMALLOC with HAVE_ARCH_HUGE_VMAP
bpf: use bytes instead of pages for bpf_jit_[charge|uncharge]_modmem
bpf: use size instead of pages in bpf_binary_header
bpf: add a pointer of bpf_binary_header to bpf_prog
x86/alternative: introduce text_poke_jit
bpf: introduce bpf_prog_pack allocator
bpf, x86_64: use bpf_prog_pack allocator

arch/x86/Kconfig                     |   1 +
arch/x86/include/asm/text-patching.h |   1 +
arch/x86/kernel/alternative.c        |  28 ++++
arch/x86/net/bpf_jit_comp.c          |  93 ++++++++++--
include/linux/bpf.h                  |   4 +-
include/linux/filter.h               |  23 ++-
kernel/bpf/core.c                    | 213 ++++++++++++++++++++++++---
kernel/bpf/trampoline.c              |   6 +-
8 files changed, 328 insertions(+), 41 deletions(-)

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2.30.2