Re: [RFC][PATCH] introduce ptr_diff()

Andi Kleen
2010-08-19T12:23:15Z

Namhyung Kim <namhyung@gmail.com> writes:

> When I compiled allyesconfig'ed kernel with C=1, I got 1519 lines of
> following message:
>
> include/linux/mm.h:599:16: warning: potentially expensive pointer subtraction
>
> which is around 10% of total warnings. this was caused by page_to_pfn() macro
> so I think it's worth to remove it by calculating pointer subtraction
> manually.

IMHO it would be better to simply disable the warning in sparse instead
of uglying the code just to work around sparse bogosity. It doesnt' seem
to make much sense. A subtraction followed by a shift is not expensive.

-Andi

--
ak@linux.intel.com -- Speaking for myself only.