On Mon, Jun 16, 2014 at 11:49:34PM +0300, Kirill A. Shutemov wrote: > On Mon, Jun 16, 2014 at 03:35:48PM -0400, Waiman Long wrote: > > In the __split_huge_page_map() function, the check for > > page_mapcount(page) is invariant within the for loop. Because of the > > fact that the macro is implemented using atomic_read(), the redundant > > check cannot be optimized away by the compiler leading to unnecessary > > read to the page structure.
And atomic_read() is *not* atomic operation. It's implemented as dereferencing though cast to volatile, which suppress compiler optimization, but doesn't affect what CPU can do with the variable. So I doubt difference will be measurable anywhere. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
