On Wed 25-01-17 11:03:53, hejianet wrote: > > > On 25/01/2017 12:54 AM, Michal Hocko wrote: > > On Tue 24-01-17 15:49:03, Jia He wrote: > > > Currently there is no hard limitation for kswapd retry times if no progress > > > is made. > > > > Yes, because the main objective of the kswapd is to balance all memory > > zones. So having a hard limit on retries doesn't make any sense. > > > But do you think even when there is no any process, kswapd still need > to run and take the cpu usage uselessly? The question is whether we can get into such a state during reasonable workloads. So far you haven't explained what you are seeing and on which kernel version. > > > Then kswapd will take 100% for a long time. > > > > Where it is spending time? > I've watched kswapd takes 100% cpu for a whole night. I assume it didn't get to sleep because your request has consumed enough memory for hugetlb pages to get below watermarks which would keep kswapd active. Is that correct? > > > In my test, I tried to allocate 4000 hugepages by: > > > echo 4000 > /proc/sys/vm/nr_hugepages > > > > > > Then,kswapd will take 100% cpu for a long time. > > > > > > The numa layout is: > > > available: 7 nodes (0-6) > > > node 0 cpus: 0 1 2 3 4 5 6 7 > > > node 0 size: 6611 MB > > > node 0 free: 1103 MB > > > node 1 cpus: > > > node 1 size: 12527 MB > > > node 1 free: 8477 MB > > > node 2 cpus: > > > node 2 size: 15087 MB > > > node 2 free: 11037 MB > > > node 3 cpus: > > > node 3 size: 16111 MB > > > node 3 free: 12060 MB > > > node 4 cpus: 8 9 10 11 12 13 14 15 > > > node 4 size: 24815 MB > > > node 4 free: 20704 MB > > > node 5 cpus: > > > node 5 size: 4095 MB > > > node 5 free: 61 MB > > > node 6 cpus: > > > node 6 size: 22750 MB > > > node 6 free: 18716 MB > > > > > > The cause is kswapd will loop for long time even if there is no progress in > > > balance_pgdat. > > > > How does this solve anything? If the kswapd just backs off then the more > > work has to be done in the direct reclaim context. > What if there is still no progress in direct context? Then we trigger the OOM killer when applicable. -- Michal Hocko SUSE Labs -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
