On Sat, Sep 28, 2013 at 11:55 AM, Linus Torvalds <torva...@linux-foundation.org> wrote: > Btw, I really hate that thing. I think we should turn it back into a > spinlock. None of what it protects needs a mutex or an rwsem. > > Because you guys talk about the regression of turning it into a rwsem, > but nobody talks about the *original* regression. > > And it *used* to be a spinlock, and it was changed into a mutex back > in 2011 by commit 2b575eb64f7a. That commit doesn't even have a reason > listed for it, although my dim memory of it is that the reason was > preemption latency.
I was wondering about that too. Regarding latencies, we used to have unbounded latencies for anon_vma operations as the AVC chains could get long under some workloads; now that we index the VMAs matching a given anon_vma with an interval tree this particular source of latencies should be gone. So yes, it could be worth trying to go back to a non-sleeping lock. That said, I am very scared of using rwlock_t here, and I would much prefer we choose a fair lock (either spinlock or a new rwlock implementation which guarantees not to starve any locker thread) -- Michel Lespinasse A program is never fully debugged until the last user dies. -- 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/
