On Tue, 30 Oct 2007, Nick Piggin wrote: > Is this actually a speedup on any architecture to roll your own locking > rather than using bit spinlock?
It avoids one load from memory when allocating and the release is simply writing the page->flags back. Less instructions. > I am not exactly convinced that smp_wmb() is a good idea to have in your > unlock, rather than the normally required smp_mb() that every other open > coded lock in the kernel is using today. If you comment every code path > where a load leaking out of the critical section would not be a problem, > then OK it may be correct, but I still don't think it is worth the > maintenance overhead. I thought you agreed that release semantics only require a write barrier? The issue here is that other processors see the updates before the updates to page-flags. A load leaking out of a critical section would require that the result of the load is not used to update other information before the slab_unlock and that the source of the load is not overwritten in the critical section. That does not happen in sluib. - 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/
