oom-killer being invoked instead of swapping

Hi, I have a raspberry pi 2 on which I recently installed Ubuntu 16.04.2. After the install oom-killer has been killing processes, even when there is 1GB of swap free. I would have expected the kernel to swap something out rather than killing processes. How can I use swap rather than having oom-killer killing processes? Here is a typical oom-kill as recorded by syslog: Apr 21 15:45:01 pi2 kernel: [72182.070173] sh invoked oom-killer: gfp_mask=0x24004c0, order=2, oom_score_adj=0 Apr 21 15:45:01 pi2 kernel: [72182.070196] sh cpuset=/ mems_allowed=0 Apr 21 15:45:01 pi2 kernel: [72182.070221] CPU: 2 PID: 10341 Comm: sh Not tainted 4.4.0-1052-raspi2 #59-Ubuntu Apr 21 15:45:01 pi2 kernel: [72182.070228] Hardware name: BCM2709 Apr 21 15:45:01 pi2 kernel: [72182.070265] [<80111e94>] (unwind_backtrace) from [<8010d100>] (show_stack+0x20/0x24) Apr 21 15:45:01 pi2 kernel: [72182.070286] [<8010d100>] (show_stack) from [<8056a52c>] (dump_stack+0xc8/0x10c) Apr 21 15:45:01 pi2 kernel: [72182.070308] [<8056a52c>] (dump_stack) from [<802a888c>] (dump_header+0x68/0x1c8) Apr 21 15:45:01 pi2 kernel: [72182.070327] [<802a888c>] (dump_header) from [<80247800>] (oom_kill_process+0x36c/0x4b4) Apr 21 15:45:01 pi2 kernel: [72182.070344] [<80247800>] (oom_kill_process) from [<80247bb8>] (out_of_memory+0x1f8/0x35c) Apr 21 15:45:01 pi2 kernel: [72182.070361] [<80247bb8>] (out_of_memory) from [<8024d93c>] (__alloc_pages_nodemask+0xd38/0xd78) Apr 21 15:45:01 pi2 kernel: [72182.070378] [<8024d93c>] (__alloc_pages_nodemask) from [<8024d99c>] (__get_free_pages+0x20/0x64) Apr 21 15:45:01 pi2 kernel: [72182.070395] [<8024d99c>] (__get_free_pages) from [<801190d4>] (pgd_alloc+0x28/0x11c) Apr 21 15:45:01 pi2 kernel: [72182.070411] [<801190d4>] (pgd_alloc) from [<80121520>] (mm_init+0xd8/0x170) Apr 21 15:45:01 pi2 kernel: [72182.070427] [<80121520>] (mm_init) from [<80121bbc>] (mm_alloc+0x5c/0x68) Apr 21 15:45:01 pi2 kernel: [72182.070445] [<80121bbc>] (mm_alloc) from [<802b3ecc>] (do_execveat_common+0x280/0x744) Apr 21 15:45:01 pi2 kernel: [72182.070463] [<802b3ecc>] (do_execveat_common) from [<802b4624>] (SyS_execve+0x40/0x48) Apr 21 15:45:01 pi2 kernel: [72182.070481] [<802b4624>] (SyS_execve) from [<80108c60>] (ret_fast_syscall+0x0/0x1c) Apr 21 15:45:01 pi2 kernel: [72182.070489] Mem-Info: Apr 21 15:45:01 pi2 kernel: [72182.070510] active_anon:7968 inactive_anon:36348 isolated_anon:0 Apr 21 15:45:01 pi2 kernel: [72182.070510] active_file:35828 inactive_file:127471 isolated_file:0 Apr 21 15:45:01 pi2 kernel: [72182.070510] unevictable:0 dirty:5 writeback:0 unstable:0 Apr 21 15:45:01 pi2 kernel: [72182.070510] slab_reclaimable:15804 slab_unreclaimable:4482 Apr 21 15:45:01 pi2 kernel: [72182.070510] mapped:4644 shmem:1239 pagetables:434 bounce:0 Apr 21 15:45:01 pi2 kernel: [72182.070510] free:2363 free_pcp:0 free_cma:15 Apr 21 15:45:01 pi2 kernel: [72182.070554] Normal free:9452kB min:3836kB low:4792kB high:5752kB active_anon:31872kB inactive_anon:145392kB active_file:143312kB inactive_fi le:509884kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:966656kB managed:942128kB mlocked:0kB dirty:20kB writeback:0kB mapped:18576kB shmem:4956kB slab_r eclaimable:63216kB slab_unreclaimable:17928kB kernel_stack:1656kB pagetables:1736kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:60kB writeback_tmp:0kB page s_scanned:16 all_unreclaimable? no Apr 21 15:45:01 pi2 kernel: [72182.070563] lowmem_reserve[]: 0 0 Apr 21 15:45:01 pi2 kernel: [72182.070577] Normal: 1251*4kB (UME) 579*8kB (UME) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 9636kB Apr 21 15:45:01 pi2 kernel: [72182.070625] 165625 total pagecache pages Apr 21 15:45:01 pi2 kernel: [72182.070635] 1119 pages in swap cache Apr 21 15:45:01 pi2 kernel: [72182.070643] Swap cache stats: add 23103, delete 21984, find 25546/29364 Apr 21 15:45:01 pi2 kernel: [72182.070650] Free swap = 1004812kB Apr 21 15:45:01 pi2 kernel: [72182.070656] Total swap = 1048572kB Apr 21 15:45:01 pi2 kernel: [72182.070663] 241664 pages RAM Apr 21 15:45:01 pi2 kernel: [72182.070669] 0 pages HighMem/MovableOnly Apr 21 15:45:01 pi2 kernel: [72182.070675] 6132 pages reserved Apr 21 15:45:01 pi2 kernel: [72182.070681] 2048 pages cma reserved Apr 21 15:45:01 pi2 kernel: [72182.070688] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name Apr 21 15:45:01 pi2 kernel: [72182.070717] [ 345] 0 345 1225 228 6 0 40 0 systemd-journal Apr 21 15:45:01 pi2 kernel: [72182.070730] [ 383] 0 383 3124 36 7 0 3 0 lvmetad Apr 21 15:45:01 pi2 kernel: [72182.070744] [ 431] 0 431 2997 145 8 0 128 -1000 systemd-udevd Apr 21 15:45:01 pi2 kernel: [72182.070758] [ 684] 100 684 3064 123 7 0 28 0 systemd-timesyn Apr 21 15:45:01 pi2 kernel: [72182.070771] [ 701] 0 701 592 38 6 0 4 0 rpc.idmapd Apr 21 15:45:01 pi2 kernel: [72182.070783] [ 805] 0 805 834 287 6 0 33 0 systemd-logind Apr 21 15:45:01 pi2 kernel: [72182.070796] [ 808] 0 808 346 63 5 0 3 0 acpid Apr 21 15:45:01 pi2 kernel: [72182.070808] [ 815] 0 815 1130 129 7 0 19 0 cron Apr 21 15:45:01 pi2 kernel: [72182.070821] [ 819] 0 819 7684 292 10 0 1 0 lxcfs Apr 21 15:45:01 pi2 kernel: [72182.070834] [ 822] 107 822 1226 296 6 0 48 -900 dbus-daemon Apr 21 15:45:01 pi2 kernel: [72182.070846] [ 831] 104 831 7794 168 9 0 122 0 rsyslogd Apr 21 15:45:01 pi2 kernel: [72182.070859] [ 833] 0 833 9084 635 12 0 63 0 accounts-daemon Apr 21 15:45:01 pi2 kernel: [72182.070871] [ 836] 0 836 712 55 6 0 33 0 atd Apr 21 15:45:01 pi2 kernel: [72182.070883] [ 854] 0 854 8711 305 13 0 57 0 polkitd Apr 21 15:45:01 pi2 kernel: [72182.070896] [ 1002] 113 1002 29479 1911 30 0 4528 0 named Apr 21 15:45:01 pi2 kernel: [72182.070909] [ 1012] 0 1012 1997 225 7 0 104 -1000 sshd Apr 21 15:45:01 pi2 kernel: [72182.070922] [ 1015] 114 1015 2560 865 10 0 945 0 dhcpd Apr 21 15:45:01 pi2 kernel: [72182.070935] [ 1045] 0 1045 1359 97 6 0 80 0 rpcbind Apr 21 15:45:01 pi2 kernel: [72182.070948] [ 1049] 0 1049 1420 516 6 0 119 0 rpc.mountd Apr 21 15:45:01 pi2 kernel: [72182.070962] [ 1143] 0 1143 832 118 6 0 17 0 irqbalance Apr 21 15:45:01 pi2 kernel: [72182.070974] [ 1170] 0 1170 862 61 5 0 25 0 agetty Apr 21 15:45:01 pi2 kernel: [72182.070987] [ 1172] 0 1172 908 10 6 0 19 0 agetty Apr 21 15:45:01 pi2 kernel: [72182.071000] [ 1254] 0 1254 10969 1791 16 0 710 0 fail2ban-server Apr 21 15:45:01 pi2 kernel: [72182.071012] [ 1263] 0 1263 2225 1240 8 0 45 0 apache2 Apr 21 15:45:01 pi2 kernel: [72182.071025] [ 1358] 0 1358 7968 143 9 0 65 0 master Apr 21 15:45:01 pi2 kernel: [72182.071037] [ 1360] 112 1360 8020 335 9 0 45 0 qmgr Apr 21 15:45:01 pi2 kernel: [72182.071050] [ 1716] 1000 1716 1581 32 8 0 409 0 systemd Apr 21 15:45:01 pi2 kernel: [72182.071062] [ 1720] 1000 1720 1813 33 7 0 397 0 (sd-pam) Apr 21 15:45:01 pi2 kernel: [72182.071075] [ 1912] 0 1912 2945 119 11 0 165 0 sshd Apr 21 15:45:01 pi2 kernel: [72182.071088] [ 1946] 1000 1946 4041 1235 14 0 146 0 sshd Apr 21 15:45:01 pi2 kernel: [72182.071100] [ 1947] 1000 1947 36295 35191 75 0 10 0 unison Apr 21 15:45:01 pi2 kernel: [72182.071114] [ 6694] 33 6694 58348 900 36 0 45 0 apache2 Apr 21 15:45:01 pi2 kernel: [72182.071127] [ 6695] 33 6695 58092 899 36 0 45 0 apache2 Apr 21 15:45:01 pi2 kernel: [72182.071141] [10335] 112 10335 7986 721 8 0 0 0 pickup Apr 21 15:45:01 pi2 kernel: [72182.071153] [10337] 0 10337 1470 504 7 0 5 0 cron Apr 21 15:45:01 pi2 kernel: [72182.071166] [10338] 1000 10338 365 101 4 0 0 0 sh Apr 21 15:45:01 pi2 kernel: [72182.071179] [10339] 1000 10339 3084 2179 10 0 0 0 optus-status Apr 21 15:45:01 pi2 kernel: [72182.071191] [10340] 1000 10340 365 93 5 0 0 0 sh Apr 21 15:45:01 pi2 kernel: [72182.071203] [10341] 1000 10341 365 16 4 0 0 0 sh Apr 21 15:45:01 pi2 kernel: [72182.071212] Out of memory: Kill process 1947 (unison) score 70 or sacrifice child Apr 21 15:45:01 pi2 kernel: [72182.078994] Killed process 1947 (unison) total-vm:145180kB, anon-rss:139988kB, file-rss:776kB Apr 21 15:45:02 pi2 systemd[1]: Stopping User Manager for UID 1000... Apr 21 15:45:02 pi2 systemd[1716]: Stopped target Default. Apr 21 15:45:02 pi2 systemd[1716]: Reached target Shutdown. Apr 21 15:45:02 pi2 systemd[1716]: Stopped target Basic System. Apr 21 15:45:02 pi2 systemd[1716]: Stopped target Paths. Apr 21 15:45:02 pi2 systemd[1716]: Stopped target Sockets. Apr 21 15:45:02 pi2 systemd[1716]: Stopped target Timers. Apr 21 15:45:02 pi2 systemd[1716]: Starting Exit the Session... Apr 21 15:45:02 pi2 systemd[1716]: Received SIGRTMIN+24 from PID 10345 (kill). Apr 21 15:45:02 pi2 systemd[1]: Stopped User Manager for UID 1000. Apr 21 15:45:02 pi2 systemd[1]: Removed slice User Slice of kim.