On Mon, Dec 12, 2011 at 06:13:11AM +0100, Andi Kleen wrote: > > It's ~180 bytes, so it's not really that small. > > Quite small compared to what real code uses. And also fixed > size. > > > > > > is on the new stack. ISTs are not used for interrupts, only for > > > some special exceptions. > > > > IST = ??? > > That's a hardware mechanism on x86-64 to switch stacks > (Interrupt Stack Table or somesuch) > > With ISTs it would have been possible to move the the pt_regs too, > but the software mechanism is somewhat simpler. > > > at the top of the stack frame? Is the stack unwinder walking back > > across the interrupt stack to the previous task stack? > > Yes, the unwinder knows about all the extra stacks (interrupt > and exception stacks) and crosses them as needed. > > BTW I suppose it wouldn't be all that hard to add more stacks and > switch to them too, similar to what the 32bit do_IRQ does. > Perhaps XFS could just allocate its own stack per thread > (or maybe only if it detects some specific configuration that > is known to need much stack) That's possible, but rather complex, I think. > It would need to be per thread if you could sleep inside them. Yes, we'd need to sleep, do IO, possibly operate within a transaction context, etc, and a workqueue handles all these cases without having to do anything special. Splitting the stack at a logical point is probably better, such as this patch: http://oss.sgi.com/archives/xfs/2011-07/msg00443.html Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>