2013/7/20 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>: > On Fri, 19 Jul 2013 07:47:02 +0800 Jerry <uulinux@xxxxxxxxx> wrote: > >> 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 >> ..... > > Good heavens. > >> In my patch, I think compiler would optimize "if (20 > PAGE_SIZE)", it >> won't generate any machine instruction. Just a guarantee. > > Well the existing code is a bit silly looking. Why can't we just do > > /* round applicable memory size up to nearest megabyte */ > if (PAGE_SHIFT < 20) > numentries = round_up(nr_kernel_pages, (1 << 20)/PAGE_SIZE); > > or similar? Great. I have adjusted these code lines, and sent the latest one. -- 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>