On Thu, 2011-05-12 at 22:29 +0200, Johannes Weiner wrote: > On Thu, May 12, 2011 at 03:04:12PM -0500, James Bottomley wrote: > > On Thu, 2011-05-12 at 14:44 -0500, James Bottomley wrote: > > > On Thu, 2011-05-12 at 13:37 -0500, James Bottomley wrote: > > > > On Thu, 2011-05-12 at 18:55 +0300, Pekka Enberg wrote: > > > > > On Thu, 2011-05-12 at 10:43 -0500, James Bottomley wrote: > > > > > > However, since you admit even you see problems, let's concentrate on > > > > > > fixing them rather than recriminations? > > > > > > > > > > Yes, please. So does dropping max_order to 1 help? > > > > > PAGE_ALLOC_COSTLY_ORDER is set to 3 in 2.6.39-rc7. > > > > > > > > Just booting with max_slab_order=1 (and none of the other patches > > > > applied) I can still get the machine to go into kswapd at 99%, so it > > > > doesn't seem to make much of a difference. > > > > > > > > Do you want me to try with the other two patches and max_slab_order=1? > > > > > > OK, so patches 1 + 2 plus setting slub_max_order=1 still manages to > > > trigger the problem (kswapd spinning at 99%). This is still with > > > PREEMPT; it's possible that non-PREEMPT might be better, so I'll try > > > patches 1+2+3 with PREEMPT just to see if the perturbation is caused by > > > it. > > > > Confirmed, I'm afraid ... I can trigger the problem with all three > > patches under PREEMPT. It's not a hang this time, it's just kswapd > > taking 100% system time on 1 CPU and it won't calm down after I unload > > the system. > > That is kind of expected, though. If one CPU is busy with a streaming > IO load generating new pages, kswapd is busy reclaiming the old ones > so that the generator does not have to do the reclaim itself. > > By unload, do you mean stopping the generator? Correct. > And if so, how quickly > after you stop the generator does kswapd go back to sleep? It doesn't. At least not on its own; the CPU stays pegged. If I start other work (like a kernel compile), then sometimes it does go back to nothing. I'm speculating that this is the hang case for non-PREEMPT. James -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
