On Wed, Aug 27, 2008 at 9:21 AM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote: >> By your logic though, XFS on x86 should work fine with 4K stacks - >> many will attest that it does not and blows up due to stack issues. >> >> I have first hand experiences of things blowing up with deep call >> chains when using 4K stacks where 8K worked just fine on same >> workload. >> >> So there is definitely some other problem with 4K stacks. > > Nothing of the sort. If it blows up with a 4K stack it will almost > certainly blow up with an 8K stack *eventually* - when a heavy stack usage > coincides with a heavy stack using IRQ handler. > > You won't catch it in simple testing, you won't catch it in trivial > simulation and it'll be incredibly hard to reproduce. Not the kind of bug > you want in a production system really. IRQ stacks make things much more > predictable. I see - so if I end up having a workload on 8k where heavy stack using IRQs and deep kernel call chains come at the same time - even 8K will blow up. So 4K will blow too except that it doesn't require IRQs also to use heavy stack, just XFS is good enough :) It then seems like the IRQs using lot of stack is not so much of a problem in the current kernel as much as deeper call chains and stack usage of normal non-irq path code is. So 8k makes it possible for the deeper call chains of non-irq path to survive since they get better part of the 8K to themselves and IRQs can do with less almost always. At least that's what I can derive from the fact that we do not have lots of reports of 8K stack blowing up. Thanks Parag -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
