On Thu, 2011-07-28 at 18:19 +0800, Mel Gorman wrote: > On Thu, Jul 28, 2011 at 04:11:28PM +0800, Alex Shi wrote: > > There 2 place to read pgdat in kswapd. One is return from a successful > > balance, another is waked up from sleeping. But the new_order and > > new_classzone_idx are not assigned after kswapd_try_to_sleep(), that > > will cause a bug in the following scenario. > > > > After the last time successful balance, kswapd goes to sleep. So the > > new_order and new_classzone_idx were assigned to 0 and MAX-1 since there > > is no new wakeup during last time balancing. Now, a new wakeup came and > > finish balancing successful with order > 0. But since new_order is still > > 0, this time successful balancing were judged as a failed balance. so, > > if there is another new wakeup coming during balancing, kswapd cann't > > read this and still want to try to sleep. And if the new wakeup is a > > tighter request, kswapd may goes to sleep, not to do balancing. That is > > incorrect. > > > > So, to avoid above problem, the new_order and new_classzone_idx need to > > be assigned for later successful comparison. > > > > Other than a different changelog, this is identical to > https://lkml.org/lkml/2011/6/30/157 so
Oops, I didn't aware this, otherwise it will save me several hours to explain what the problem in current code to Shaohua and others. :) In fact, I still hold another patch of kswapd and some idea of how to kswapd working that want to talk with you. > > Acked-by: Mel Gorman <[email protected]> > > It won't be merged to -stable until it goes to mainline though so > minimally you need to post this to linux-mm. > > For -stable, you should explain why it is a candidate. I didn't push > the patch at the time because user problems were already resolved > and I wanted the merged for 3.0 before revisiting it. What problem > did you observe without this patch? With the lack of reference to > the other thread or the previous patch, I'm assuming you found and > solved the problem independently and I'd like to add a test case. Actually, our LKP testing didn't find this problem on this point. Even with the patch, performance has no change on our machines. I just find this by my eyes. BTW, I have tracked our benchmarks for their hot path in kernel. The most exercised benchmark on kswapd is no more than 5% of system load. that is fio mmap rand write or randrw. Do you have some benchmark can use kswapd much? BTW, our project http://kernel-perf.sourceforge.net/ > > Thanks. > _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
