On 06/18/2013 05:37 AM, David Rientjes wrote: > On Mon, 17 Jun 2013, Zhang Yanfei wrote: > >>> I don't understand the justification at all, current_order being unlikely >>> greater than or equal to pageblock_order / 2 doesn't imply at all that >>> it's unlikely that current_order is greater than or equal to >>> pageblock_order. >>> >> >> hmmm... I am confused. Since current_order is >= pageblock_order / 2 is >> unlikely, >> why current_order is >= pageblock_order isn't unlikely. Or there are other >> tips? >> >> Actually, I am also a little confused about why current_order should be >> unlikely greater than or equal to pageblock_order / 2. When borrowing pages >> with other migrate_type, we always search from MAX_ORDER-1, which is greater >> or equal to pageblock_order. >> > > Look at what is being done in the function: current_order loops down from > MAX_ORDER-1 to the order passed. It is not at all "unlikely" that > current_order is greater than pageblock_order, or pageblock_order / 2. > > MAX_ORDER is typically 11 and pageblock_order is typically 9 on x86. > Integer division truncates, so pageblock_order / 2 is 4. For the first > eight iterations, it's guaranteed that current_order >= pageblock_order / > 2 if it even gets that far! > > So just remove the unlikely() entirely, it's completely bogus.
I see. Thanks! I will send another patch. -- Thanks. Zhang Yanfei -- 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/
