On 05/01/2014 08:11 AM, Mel Gorman wrote: > On Thu, May 01, 2014 at 07:35:47AM -0700, Dave Hansen wrote: >> On 05/01/2014 01:44 AM, Mel Gorman wrote: >>> X86 prefers the use of unsigned types for iterators and there is a >>> tendency to mix whether a signed or unsigned type if used for page >>> order. This converts a number of sites in mm/page_alloc.c to use >>> unsigned int for order where possible. >> >> Does this actually generate any different code? I'd actually expect >> something like 'order' to be one of the easiest things for the compiler >> to figure out an absolute range on. > > Yeah, it generates different code. Considering that this patch affects an > API that can be called external to the code block how would the compiler > know what the range of order would be in all cases?
The compiler comprehends that if you do a check against a constant like MAX_ORDER early in the function that the the variable now has a limited range, like the check we do first-thing in __alloc_pages_slowpath(). The more I think about it, at least in page_alloc.c, I don't see any checks for order<0, which means the compiler isn't free to do this anyway. Your move over to an unsigned type gives that check for free essentially. So this makes a lot of sense in any case. I was just curious if it affected the code. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
