Adding my self > On 11-Jan-2017, at 11:08 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > [CC Minchan and Sergey for the zram part] > > On Thu 12-01-17 01:16:11, Cheng-yu Lee wrote: >> Hi community, >> >> I have a x86_64 Chromebook running 3.14 kernel with 8G of memory. Using > > Do you see the same with the current Linus tree? > >> zram with swap size set to ~12GB. When in low memory, kswapd is awaken to >> reclaim pages, but under some circumstances the kernel can not find pages >> to reclaim while I'm sure there're still plenty of memory which could be >> reclaimed from background processes (For example, I run some C programs >> which just malloc() lots of memory and get suspended in the background. >> There's no reason they could't be swapped). The consequence is that most of >> CPU time is spent on page reclamation. The system hangs or becomes very >> laggy for a long period. Sometimes it even triggers a kernel panic by the >> hung task detector like: >> <0>[46246.676366] Kernel panic - not syncing: hung_task: blocked tasks >> >> I've added kernel message to trace the problem. I found shrink_inactive_list() >> can barely find any page to reclaim. More precisely, when the problem >> happens, lots of page have _count > 2 in __remove_mapping(). So the >> condition at line 662 of vmscan.c holds: >> http://lxr.free-electrons.com/source/mm/vmscan.c#L662 >> Thus the kernel fails to reclaim those pages at line 1209 >> http://lxr.free-electrons.com/source/mm/vmscan.c#L1209 > > I assume that you are talking about the anonymous LRU > >> It's weird that the inactive anonymous list is huge (several GB), but >> nothing can really be freed. So I did some hack to see if moving more pages >> from the active list helps. I commented out the "inactive_list_is_low()" >> checking at line 2420 >> in shrink_node_memcg() so shrink_active_list() is always called. >> http://lxr.free-electrons.com/source/mm/vmscan.c#L2420 >> It turns out that the hack helps. If moving more pages from the active >> list, kswapd works smoothly. The whole 12G zram can be used up before >> system enters OOM condition. >> >> Any idea why the whole inactive anonymous LRU is occupied by pages which >> can not be freed for la long time (several minutes before system dies) ? >> Are there any parameters I can tune to help the situation ? I've tried >> swappiness but it doesn't help. >> >> An alternative is to patch the kernel to call shrink_active_list() more >> frequently when it finds there's nothing that can be reclaimed . But I am >> not sure if it's the right direction. Also it's not so trivial to figure >> out where to add the call. >> >> Thanks, >> Cheng-Yu > > -- > 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> -- 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