On 10/01, Paul E. McKenney wrote: > > On Tue, Oct 01, 2013 at 04:14:29PM +0200, Oleg Nesterov wrote: > > > > But please note another email, it seems to me we can simply kill > > cpuhp_seq and all the barriers in cpuhp_readers_active_check(). > > If you don't have cpuhp_seq, you need some other way to avoid > counter overflow. I don't think so. Overflows (espicially "unsigned") should be fine and in fact we can't avoid them. Say, a task does get() on CPU_0 and put() on CPU_1, after that we have CTR[0] == 1, CTR[1] = (unsigned)-1 iow, the counter was already overflowed (underflowed). But this is fine, all we care about is CTR[0] + CTR[1] == 0, and this is only true because of another overflow. But probably you meant another thing, > Which might be provided by limited number of > tasks, or, on 64-bit systems, 64-bit counters. perhaps you meant that max_threads * max_depth can overflow the counter? I don't think so... but OK, perhaps this counter should be u_long. But how cpuhp_seq can help? Oleg. -- 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>