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, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>