2013/7/19 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>: > On Fri, 19 Jul 2013 00:56:12 +0800 Jerry <uulinux@xxxxxxxxx> wrote: > >> When PAGE_SHIFT > 20, the result of "20 - PAGE_SHIFT" is negative. The >> calculating here will generate an unexpected result. In addition, if >> PAGE_SHIFT > 20, The memory size represented by numentries was already >> integral multiple of 1MB. >> > > If you tell me that you have a machine which has PAGE_SIZE=2MB and this > was the only problem which prevented Linux from running on that machine > then I'll apply the patch ;) > Hi Morton: I just "grep -rn "#define\s\+PAGE_SHIFT" arch/", and find the PAGE_SHIFT in some architecture is very big. such as the following in "arch/hexagon/include/asm/page.h" .... #ifdef CONFIG_PAGE_SIZE_256KB #define PAGE_SHIFT 18 #define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_256KB #endif #ifdef CONFIG_PAGE_SIZE_1MB #define PAGE_SHIFT 20 #define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_1MB #endif ..... Maybe the day of "A 2MB page" is not far. :-) I know it is just a latent issue. Even if it won't generate a error when PAGE_SIZE == 20, the calculating here is not necessary. In my mind, compiler would optimize the calculating at that situation. But it is a little tricky. In my patch, I think compiler would optimize "if (20 > PAGE_SIZE)", it won't generate any machine instruction. Just a guarantee. -- I love linux!!! -- 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>