On Thu, 3 Sep 2015 12:14:51 +0800 gang.chen.5i5j@xxxxxxxxx wrote:
> From: Chen Gang <gang.chen.5i5j@xxxxxxxxx>
>
> Call the function pointer directly, then let code a bit simpler.
>
> ...
>
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2012,10 +2012,8 @@ unsigned long
> get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
> unsigned long pgoff, unsigned long flags)
> {
> - unsigned long (*get_area)(struct file *, unsigned long,
> - unsigned long, unsigned long, unsigned long);
> -
> unsigned long error = arch_mmap_check(addr, len, flags);
> +
> if (error)
> return error;
>
> @@ -2023,10 +2021,12 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
> if (len > TASK_SIZE)
> return -ENOMEM;
>
> - get_area = current->mm->get_unmapped_area;
> if (file && file->f_op->get_unmapped_area)
> - get_area = file->f_op->get_unmapped_area;
> - addr = get_area(file, addr, len, pgoff, flags);
> + addr = file->f_op->get_unmapped_area(file, addr, len,
> + pgoff, flags);
> + else
> + addr = current->mm->get_unmapped_area(file, addr, len,
> + pgoff, flags);
> if (IS_ERR_VALUE(addr))
> return addr;
size(1) says this generates more object code. And that probably means
slightly worse code. I didn't investigate, but probably the compiler
is now preparing those five args at two different sites.
Which is pretty dumb of it - the compiler could have stacked the args
first, then chosen the appropriate function to call.
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