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

[Song Liu <songliubraving@fb.com>]

> On Dec 17, 2021, at 8:43 AM, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> 
> On Fri, Dec 17, 2021 at 8:42 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
>> 
>> On Thu, Dec 16, 2021 at 5:53 PM Song Liu <songliubraving@fb.com> wrote:
>>> 
>>> 
>>> 
>>>> On Dec 16, 2021, at 12:06 PM, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>>>> 
>>>> On Tue, Dec 14, 2021 at 10:01 PM Song Liu <song@kernel.org> wrote:
>>>>> 
>>>>> 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. 

Thanks,
Song


> 
>>> Thanks,
>>> Song
>>> 
>>> 
>>>> 
>>>> [0] https://github.com/kernel-patches/bpf/runs/4530372387?check_suite_focus=true
>>>> 
>>>>> 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(-)
>>>>> 
>>>>> --
>>>>> 2.30.2
>>>