On 03/18/2013 11:53 AM, Yinghai Lu wrote: > On Mon, Mar 18, 2013 at 3:21 AM, Lin Feng <linf...@cn.fujitsu.com> wrote: >> For x86 PUD_SHIFT is 30 and PMD_SHIFT is 21, so the consequence of >> (PUD_SHIFT-PMD_SHIFT)/2 is 4. Update the comments to the code. >> >> Cc: Yinghai Lu <ying...@kernel.org> >> Signed-off-by: Lin Feng <linf...@cn.fujitsu.com> >> --- >> arch/x86/mm/init.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c >> index 59b7fc4..637a95b 100644 >> --- a/arch/x86/mm/init.c >> +++ b/arch/x86/mm/init.c >> @@ -389,7 +389,7 @@ static unsigned long __init init_range_memory_mapping( >> return mapped_ram_size; >> } >> >> -/* (PUD_SHIFT-PMD_SHIFT)/2 */ >> +/* (PUD_SHIFT-PMD_SHIFT)/2+1 */ >> #define STEP_SIZE_SHIFT 5 >> void __init init_mem_mapping(void) >> { > > 9/2=4.5, so it becomes 5. >
No, it doesn't. This is C, not elementary school Now I'm really bothered. The comment doesn't say *why* (PUD_SHIFT-PMD_SHIFT)/2 or any other variant is correct, furthermore I suspect that the +1 is misplaced. However, what is really needed is: 1. Someone needs to explain what the logic should be and why, and 2. replace the macro with a symbolic macro, not with a constant and a comment explaining, incorrectly, how that value was derived. -hpa -- 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/