On Tue, 2007-05-08 at 13:40 +0200, Nick Piggin wrote: > This patch trades a page flag for a significant improvement in the unlock_page > fastpath. Various problems in the previous version were spotted by Hugh and > Ben (and fixed in this one). > > Comments? > > -- > > Speed up unlock_page by introducing a new page flag to signal that there are > page waitqueue waiters for PG_locked. This means a memory barrier and a random > waitqueue hash cacheline load can be avoided in the fastpath when there is no > contention.
I'm not 100% familiar with the exclusive vs. non exclusive wait thingy but wake_up_page() does __wake_up_bit() which calls __wake_up() with nr_exclusive set to 1. Doesn't that mean that only one waiter will be woken up ? If that's the case, then we lose because we'll have clear PG_waiters but only wake up one of them. Waking them all would fix it but at the risk of causing other problems... Maybe PG_waiters need to actually be a counter but if that is the case, then it complicates things even more. Any smart idea ? Ben. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
