On 02/27/2014 02:06 PM, Linus Torvalds wrote: > On Thu, Feb 27, 2014 at 1:59 PM, Dave Hansen > <[email protected]> wrote: >> >> Also, the folks with larger base bage sizes probably don't want a >> FAULT_AROUND_ORDER=4. That's 1MB of fault-around for ppc64, for example. > > Actually, I'd expect that they won't mind, because there's no real > extra cost (the costs are indepenent of page size).
The question is really whether or not we ever access the mapping that we faulted around, though. If we never access it, then the cost (however small it was) is a loss. That's the mechanism that I'd expect causes Kirill's numbers to go up after they hit their minimum at ~order-4. > For small mappings the mapping size itself will avoid the > fault-around, and for big mappings they'll get the reduced page > faults. Kirill's git test suite runs did show that it _can_ hurt in some cases. Orders 1 to 4 were improvements. But, Order-5 was even with the baseline, and orders 7 and 9 got a bit worse: > Git test suite (make -j60 test) > FAULT_AROUND_ORDER Baseline 1 3 > 4 5 7 9 > minor-faults 129,591,823 99,200,751 66,106,718 > 57,606,410 51,510,808 45,776,813 44,085,515 > time, seconds 66.087215026 64.784546905 64.401156567 > 65.282708668 66.034016829 66.793780811 67.237810413 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
