We've been running into the OOM killer despite nearly half of our memory being used for the FS cache. We've been logging memory stats once per minute (as reported by top), but there seems to be plenty of availability.
... Mem: 15339640k total, 15268304k used, 71336k free, 3152k buffers Swap: 0k total, 0k used, 0k free, 6608384k cached Mem: 15339640k total, 14855280k used, 484360k free, 13748k buffers Swap: 0k total, 0k used, 0k free, 6481852k cached [OOM killer: postgres killed] Mem: 15339640k total, 8212200k used, 7127440k free, 32776k buffers Swap: 0k total, 0k used, 0k free, 2394444k cached ...
OOM details from syslog:
... Jun 10 05:45:25 db kernel: [11209156.840462] wal-e invoked oom-killer: gfp_mask=0x201da, order=0, oom_adj=0, oom_score_adj=0 Jun 10 05:45:25 db kernel: [11209156.840469] wal-e cpuset=/ mems_allowed=0 Jun 10 05:45:25 db kernel: [11209156.840474] Pid: 7963, comm: wal-e Not tainted 3.2.0-43-virtual #68-Ubuntu Jun 10 05:45:25 db kernel: [11209156.840477] Call Trace: Jun 10 05:45:25 db kernel: [11209156.840498] [<ffffffff81119711>] dump_header+0x91/0xe0 Jun 10 05:45:25 db kernel: [11209156.840502] [<ffffffff81119a95>] oom_kill_process+0x85/0xb0 Jun 10 05:45:25 db kernel: [11209156.840506] [<ffffffff81119e3a>] out_of_memory+0xfa/0x220 Jun 10 05:45:25 db kernel: [11209156.840511] [<ffffffff8111f823>] __alloc_pages_nodemask+0x8c3/0x8e0 Jun 10 05:45:25 db kernel: [11209156.840520] [<ffffffff81216e00>] ? noalloc_get_block_write+0x30/0x30 Jun 10 05:45:25 db kernel: [11209156.840528] [<ffffffff811566c6>] alloc_pages_current+0xb6/0x120 Jun 10 05:45:25 db kernel: [11209156.840534] [<ffffffff81116637>] __page_cache_alloc+0xb7/0xd0 Jun 10 05:45:25 db kernel: [11209156.840539] [<ffffffff81118602>] filemap_fault+0x212/0x3c0 Jun 10 05:45:25 db kernel: [11209156.840553] [<ffffffff81138c32>] __do_fault+0x72/0x550 Jun 10 05:45:25 db kernel: [11209156.840557] [<ffffffff8113c2ea>] handle_pte_fault+0xfa/0x200 Jun 10 05:45:25 db kernel: [11209156.840562] [<ffffffff8100638e>] ? xen_pmd_val+0xe/0x10 Jun 10 05:45:25 db kernel: [11209156.840567] [<ffffffff81005309>] ? __raw_callee_save_xen_pmd_val+0x11/0x1e Jun 10 05:45:25 db kernel: [11209156.840571] [<ffffffff8113d559>] handle_mm_fault+0x269/0x370 Jun 10 05:45:25 db kernel: [11209156.840576] [<ffffffff8100a56d>] ? xen_force_evtchn_callback+0xd/0x10 Jun 10 05:45:25 db kernel: [11209156.840581] [<ffffffff8100ad42>] ? check_events+0x12/0x20 Jun 10 05:45:25 db kernel: [11209156.840589] [<ffffffff8165b3cb>] do_page_fault+0x14b/0x520 Jun 10 05:45:25 db kernel: [11209156.840594] [<ffffffff81160d64>] ? kmem_cache_free+0x104/0x110 Jun 10 05:45:25 db kernel: [11209156.840600] [<ffffffff811ba2c8>] ? ep_remove+0xa8/0xc0 Jun 10 05:45:25 db kernel: [11209156.840604] [<ffffffff811bb133>] ? sys_epoll_ctl+0xb3/0x3d0 Jun 10 05:45:25 db kernel: [11209156.840614] [<ffffffff81658035>] page_fault+0x25/0x30 Jun 10 05:45:25 db kernel: [11209156.840617] Mem-Info: Jun 10 05:45:25 db kernel: [11209156.840618] Node 0 DMA per-cpu: Jun 10 05:45:25 db kernel: [11209156.840622] CPU 0: hi: 0, btch: 1 usd: 0 Jun 10 05:45:25 db kernel: [11209156.840624] CPU 1: hi: 0, btch: 1 usd: 0 Jun 10 05:45:25 db kernel: [11209156.840627] CPU 2: hi: 0, btch: 1 usd: 0 Jun 10 05:45:25 db kernel: [11209156.840629] CPU 3: hi: 0, btch: 1 usd: 0 Jun 10 05:45:25 db kernel: [11209156.840631] Node 0 DMA32 per-cpu: Jun 10 05:45:25 db kernel: [11209156.840634] CPU 0: hi: 186, btch: 31 usd: 30 Jun 10 05:45:25 db kernel: [11209156.840637] CPU 1: hi: 186, btch: 31 usd: 47 Jun 10 05:45:25 db kernel: [11209156.840639] CPU 2: hi: 186, btch: 31 usd: 15 Jun 10 05:45:25 db kernel: [11209156.840641] CPU 3: hi: 186, btch: 31 usd: 2 Jun 10 05:45:25 db kernel: [11209156.840643] Node 0 Normal per-cpu: Jun 10 05:45:25 db kernel: [11209156.840646] CPU 0: hi: 186, btch: 31 usd: 0 Jun 10 05:45:25 db kernel: [11209156.840648] CPU 1: hi: 186, btch: 31 usd: 14 Jun 10 05:45:25 db kernel: [11209156.840650] CPU 2: hi: 186, btch: 31 usd: 0 Jun 10 05:45:25 db kernel: [11209156.840653] CPU 3: hi: 186, btch: 31 usd: 1 Jun 10 05:45:25 db kernel: [11209156.840658] active_anon:3616567 inactive_anon:4798 isolated_anon:0 Jun 10 05:45:25 db kernel: [11209156.840660] active_file:98 inactive_file:168 isolated_file:20 Jun 10 05:45:25 db kernel: [11209156.840661] unevictable:1597 dirty:73 writeback:0 unstable:0 Jun 10 05:45:25 db kernel: [11209156.840662] free:16921 slab_reclaimable:17631 slab_unreclaimable:7534 Jun 10 05:45:25 db kernel: [11209156.840663] mapped:1614529 shmem:1613928 pagetables:124012 bounce:0 Jun 10 05:45:25 db kernel: [11209156.840666] Node 0 DMA free:7888kB min:4kB low:4kB high:4kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:7632kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? yes Jun 10 05:45:25 db kernel: [11209156.840681] lowmem_reserve[]: 0 4016 15112 15112 Jun 10 05:45:25 db kernel: [11209156.840686] Node 0 DMA32 free:48368kB min:4176kB low:5220kB high:6264kB active_anon:3776804kB inactive_anon:28kB active_file:0kB inactive_file:20kB unevictable:932kB isolated(anon):0kB isolated(file):0kB present:4112640kB mlocked:932kB dirty:0kB writeback:0kB mapped:1458536kB shmem:1458632kB slab_reclaimable:17604kB slab_unreclaimable:8088kB kernel_stack:1872kB pagetables:190616kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:437 all_unreclaimable? yes Jun 10 05:45:25 db kernel: [11209156.840698] lowmem_reserve[]: 0 0 11095 11095 Jun 10 05:45:25 db kernel: [11209156.840703] Node 0 Normal free:11428kB min:11548kB low:14432kB high:17320kB active_anon:10689464kB inactive_anon:19164kB active_file:528kB inactive_file:652kB unevictable:5456kB isolated(anon):0kB isolated(file):80kB present:11362176kB mlocked:5456kB dirty:292kB writeback:0kB mapped:4999580kB shmem:4997080kB slab_reclaimable:52920kB slab_unreclaimable:22048kB kernel_stack:2584kB pagetables:305432kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:1974 all_unreclaimable? yes Jun 10 05:45:25 db kernel: [11209156.840715] lowmem_reserve[]: 0 0 0 0 Jun 10 05:45:25 db kernel: [11209156.840720] Node 0 DMA: 2*4kB 3*8kB 1*16kB 3*32kB 3*64kB 3*128kB 2*256kB 1*512kB 2*1024kB 2*2048kB 0*4096kB = 7888kB Jun 10 05:45:25 db kernel: [11209156.840752] Node 0 DMA32: 5813*4kB 2636*8kB 114*16kB 15*32kB 5*64kB 1*128kB 1*256kB 0*512kB 1*1024kB 0*2048kB 0*4096kB = 48372kB Jun 10 05:45:25 db kernel: [11209156.840776] Node 0 Normal: 1888*4kB 10*8kB 46*16kB 4*32kB 3*64kB 2*128kB 1*256kB 1*512kB 0*1024kB 1*2048kB 0*4096kB = 11760kB Jun 10 05:45:25 db kernel: [11209156.840788] 1615243 total pagecache pages Jun 10 05:45:25 db kernel: [11209156.840790] 0 pages in swap cache Jun 10 05:45:25 db kernel: [11209156.840801] Swap cache stats: add 0, delete 0, find 0/0 Jun 10 05:45:25 db kernel: [11209156.840803] Free swap = 0kB Jun 10 05:45:25 db kernel: [11209156.840805] Total swap = 0kB Jun 10 05:45:25 db kernel: [11209156.909794] 3934192 pages RAM Jun 10 05:45:25 db kernel: [11209156.909804] 99282 pages reserved Jun 10 05:45:25 db kernel: [11209156.909809] 18899146 pages shared Jun 10 05:45:25 db kernel: [11209156.909811] 2198511 pages non-shared Jun 10 05:45:25 db kernel: [11209156.909817] [ pid ] uid tgid total_vm rss cpu oom_adj oom_score_adj name Jun 10 05:45:25 db kernel: [11209156.909835] [ 332] 0 332 4308 109 1 0 0 upstart-udev-br Jun 10 05:45:25 db kernel: [11209156.909845] [ 346] 0 346 5384 271 2 -17 -1000 udevd Jun 10 05:45:25 db kernel: [11209156.909851] [ 408] 0 408 5364 174 2 -17 -1000 udevd ... Jun 10 05:45:25 db kernel: [11209156.910703] [ 7963] 111 7963 17456 2966 0 0 0 wal-e Jun 10 05:45:25 db kernel: [11209156.910707] [ 7968] 111 7968 1639372 2351 3 0 0 postgres Jun 10 05:45:25 db kernel: [11209156.910711] [ 7969] 111 7969 1639371 1934 2 0 0 postgres Jun 10 05:45:25 db kernel: [11209156.910716] Out of memory: Kill process 12443 (postgres) score 418 or sacrifice child Jun 10 05:45:25 db kernel: [11209156.910733] Killed process 12443 (postgres) total-vm:6555152kB, anon-rss:4600kB, file-rss:6396572kB Jun 10 05:45:30 db kernel: [11209159.293083] postgres invoked oom-killer: gfp_mask=0x201da, order=0, oom_adj=0, oom_score_adj=0 Jun 10 05:45:31 db kernel: [11209159.293091] postgres cpuset=/ mems_allowed=0 Jun 10 05:45:31 db kernel: [11209159.293095] Pid: 6508, comm: postgres Not tainted 3.2.0-43-virtual #68-Ubuntu Jun 10 05:45:31 db kernel: [11209159.293098] Call Trace: Jun 10 05:45:31 db kernel: [11209159.293111] [<ffffffff81119711>] dump_header+0x91/0xe0 Jun 10 05:45:31 db kernel: [11209159.293115] [<ffffffff81119a95>] oom_kill_process+0x85/0xb0 Jun 10 05:45:31 db kernel: [11209159.293119] [<ffffffff81119e3a>] out_of_memory+0xfa/0x220 ...
We can try increasing the resolution of these to roughly once per second, but would there be any reason for an OOM here? (We've seen http://bl0rg.krunch.be/oom-frag.html but we're working with much larger absolute amounts of memory, most of which is taken by the kernel's FS cache.)
Also including relevant parts of our postgresql.conf
below:
shared_buffers = 6GB effective_cache_size = 8GB
3.2.0-43
? Update time. The OOM killer has been through many (too many) changes over time. Some versions were really quite brain-dead about accounting for shared memory use... like PostgreSQL 9.2 and older'sshared_buffers
.shared_buffers
is still in PG9.3.shared_buffers
is still in 9.3, but it's no longer POSIX shared memory in 9.3. It's been replaced with an anonymousmmap()ed
region. That gets around some icky kernel config issues and pinning problems, though I doubt it'll make the OOM killer any less confused.