netdev - Re: [Intel-wired-lan] [PATCH 1/5] ethtool: use vmalloc

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Message-ID: <122fce2e-7335-4ace-8627-d363e241e12b@vivo.com>
Date: Thu, 14 Aug 2025 14:41:11 +0800
From: Qianfeng Rong <rongqianfeng@...o.com>
To: Paul Menzel <pmenzel@...gen.mpg.de>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>,
 Stanislav Fomichev <sdf@...ichev.me>, intel-wired-lan@...ts.osuosl.org,
 netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
 bpf@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH 1/5] ethtool: use vmalloc_array() to
 simplify code


在 2025/8/14 14:28, Paul Menzel 写道:
> [You don't often get email from pmenzel@...gen.mpg.de. Learn why this 
> is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> Dear Quianfeng,
>
>
> Thank you very much for your reply.
>
> Am 14.08.25 um 06:05 schrieb Qianfeng Rong:
>>
>> 在 2025/8/13 0:34, Paul Menzel 写道:
>
> […]
>
>>> Am 12.08.25 um 15:32 schrieb Qianfeng Rong:
>>>> Remove array_size() calls and replace vmalloc() with 
>>>> vmalloc_array() to
>>>> simplify the code and maintain consistency with existing 
>>>> kmalloc_array()
>>>> usage.
>>>
>>> You could build it without and with your patch and look if the 
>>> assembler
>>> code changes.
>>
>> Very good point, the following experiment was done:
>> //before apply patch:
>> objdump -dSl --prefix-addresses fm10k_ethtool.o > original.dis
>>
>> //after apply patch:
>> objdump -dSl --prefix-addresses fm10k_ethtool.o > patched.dis
>>
>> diff -u original.dis patched.dis | diffstat
>> patched.dis | 1578 ... 1 file changed, 785 insertions(+), 793 
>> deletions(-)
>>
>> From the above results, we can see that the assembly instructions are
>> reduced after applying the patch.
>>
>>
>> #define array_size(a, b)    size_mul(a, b)
>>
>> static inline size_t __must_check size_mul(size_t factor1, size_t 
>> factor2)
>> {
>>      size_t bytes;
>>
>>      if (check_mul_overflow(factor1, factor2, &bytes))
>>          return SIZE_MAX;
>>
>>      return bytes;
>> }
>>
>> void *__vmalloc_array_noprof(size_t n, size_t size, gfp_t flags)
>> {
>>      size_t bytes;
>>
>>      if (unlikely(check_mul_overflow(n, size, &bytes)))
>>          return NULL;
>>      return __vmalloc_noprof(bytes, flags);
>> }
>>
>> And from the code, array_size() will return SIZE_MAX after detecting
>> overflow.  SIZE_MAX is passed to vmalloc for available memory
>> verification before exiting and returning NULL. vmalloc_array()
>> will directly return NULL after detecting overflow.
>
> Awesome! Thank you for digging that up. Maybe something to add to the
> commit message. Maybe something like:
>
> `vmalloc_array()` is also optimized better, resulting in less
> instructions being used, which can be verified with:
>
> objdump -dSl --prefix-addresses <changed module>.o


Ok，I'll release v2 later.

>
>>> Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>
>
>
> Kind regards,
>
> Paul