Re: [Intel-wired-lan] [PATCH 1/5] ethtool: use vmalloc_array() to simplify code

[Qianfeng Rong]

在 2025/8/14 14:28, Paul Menzel 写道:
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>
> 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@xxxxxxxxxxxxx>
>
>
> Kind regards,
>
> Paul