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. -- 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>