On Mon, Oct 20, 2014 at 04:41:45PM -0700, Linus Torvalds wrote:
> On Mon, Oct 20, 2014 at 2:56 PM, Peter Zijlstra <pet...@infradead.org> wrote:
> > Manage the VMAs with SRCU such that we can do a lockless VMA lookup.
>
> Can you explain why srcu, and not plain regular rcu?
>
> Especially as you then *note* some of the problems srcu can have.
> Making it regular rcu would also seem to make it possible to make the
> seqlock be just a seqcount, no?
Ah, the reason I did the seqlock is because the read side will spin-wait
for &1 to go away. If the write side is preemptible that's horrid. I
used seqlock because that takes a lock (and thus disables preemption) on
the write side, but I could equally have done:
preempt_disable();
write_seqcount_begin();
...
write_seqcount_end();
preempt_disable();
Since the lock is indeed superfluous, we're already fully serialized by
mmap_sem in this path.
Using regular RCU isn't sufficient, because of PREEMPT_RCU.
--
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/
