netdev - Re: [PATCH bpf-next 2/2] bpf: fix bpf_prog_pack build HPAGE_PMD

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Date:   Thu, 10 Feb 2022 05:59:52 +0000
From:   Song Liu <songliubraving@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>
CC:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "Kernel Team" <Kernel-team@...com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH bpf-next 2/2] bpf: fix bpf_prog_pack build HPAGE_PMD_SIZE

Hi Eric, 

> On Feb 9, 2022, at 5:13 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> 
> On 2/8/22 14:05, Song Liu wrote:
>> Fix build with CONFIG_TRANSPARENT_HUGEPAGE=n with BPF_PROG_PACK_SIZE as
>> PAGE_SIZE.
>> 
>> Fixes: 57631054fae6 ("bpf: Introduce bpf_prog_pack allocator")
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Song Liu <song@...nel.org>
>> ---
>>  kernel/bpf/core.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>> 
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 306aa63fa58e..9519264ab1ee 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -814,7 +814,11 @@ int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
>>   * allocator. The prog_pack allocator uses HPAGE_PMD_SIZE page (2MB on x86)
>>   * to host BPF programs.
>>   */
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>  #define BPF_PROG_PACK_SIZE	HPAGE_PMD_SIZE
>> +#else
>> +#define BPF_PROG_PACK_SIZE	PAGE_SIZE
>> +#endif
>>  #define BPF_PROG_CHUNK_SHIFT	6
>>  #define BPF_PROG_CHUNK_SIZE	(1 << BPF_PROG_CHUNK_SHIFT)
>>  #define BPF_PROG_CHUNK_MASK	(~(BPF_PROG_CHUNK_SIZE - 1))
> 
> BTW, I do not understand with module_alloc(HPAGE_PMD_SIZE) would necessarily allocate a huge page.
> 
> I am pretty sure it does not on x86_64 and dual socket host (NUMA)
> 
> It seems you need to multiply this by num_online_nodes()  or change the way __vmalloc_node_range()
> 
> works, because it currently does:
> 
>     if (vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP)) {
>         unsigned long size_per_node;
> 
>         /*
>          * Try huge pages. Only try for PAGE_KERNEL allocations,
>          * others like modules don't yet expect huge pages in
>          * their allocations due to apply_to_page_range not
>          * supporting them.
>          */
> 
>         size_per_node = size;
>         if (node == NUMA_NO_NODE)
> <*>          size_per_node /= num_online_nodes();
>         if (arch_vmap_pmd_supported(prot) && size_per_node >= PMD_SIZE)
>             shift = PMD_SHIFT;
>         else
>             shift = arch_vmap_pte_supported_shift(size_per_node);


Thanks for highlighting this issue! I will address this in a follow up commit. 

Regards,
Song