我正在编写一个模拟器，它依赖于生成（可能）非常大的问题域。由于 RAM 无法容纳数据，我使用 4 个四内存映射文件来保存它。这是一个在具有 8GB RAM 的 64 位 Linux 上运行的 64 位应用程序。
我的应用程序在多个线程中迭代内存映射并对它们执行读写操作。然而，我的程序在启动后不久就会导致 OOM（没有发生抖动）：
[ 683.899682] Purging GPU memory, 25 pages freed, 12838 pages still pinned.
[ 683.899683] 50 and 0 pages still available in the bound and unbound GPU page lists.
[ 683.899732] Purging GPU memory, 0 pages freed, 12838 pages still pinned.
[ 683.899732] 50 and 0 pages still available in the bound and unbound GPU page lists.
[ 683.901441] gnome-shell invoked oom-killer: gfp_mask=0x240c0d0(GFP_TEMPORARY|__GFP_COMP|__GFP_ZERO), order=3, oom_score_adj=0
[ 683.901443] gnome-shell cpuset=/ mems_allowed=0
[ 683.901446] CPU: 0 PID: 1714 Comm: gnome-shell Not tainted 4.8.8-300.fc25.x86_64 #1
[ 683.901447] Hardware name: Dell Inc. XPS 13 9350/0PWNCR, BIOS 1.4.4 06/14/2016
[ 683.901449] 0000000000000286 000000006699dcf4 ffff8c743292b588 ffffffff863e5dbd
[ 683.901451] ffff8c743292b748 ffff8c73d7431f00 ffff8c743292b5f0 ffffffff8624c1f8
[ 683.901453] 000000006699dcf4 000000006699dcf4 ffffffff86e9cac0 0000000000000015
[ 683.901454] Call Trace:
[ 683.901459] [<ffffffff863e5dbd>] dump_stack+0x63/0x86
[ 683.901460] [<ffffffff8624c1f8>] dump_header+0x5c/0x1d5
[ 683.901463] [<ffffffff861bd90c>] oom_kill_process+0x20c/0x3d0
[ 683.901465] [<ffffffff860aacfe>] ? has_capability_noaudit+0x1e/0x30
[ 683.901466] [<ffffffff861bde76>] out_of_memory+0x356/0x440
[ 683.901468] [<ffffffff861c3df0>] __alloc_pages_nodemask+0xe90/0xeb0
[ 683.901470] [<ffffffff8621a055>] alloc_pages_current+0x95/0x140
[ 683.901472] [<ffffffff861e54be>] kmalloc_order_trace+0x2e/0xd0
[ 683.901508] [<ffffffffc03962b6>] ? gen9_read32+0x166/0x3a0 [i915]
[ 683.901510] [<ffffffff8622782d>] __kmalloc+0x1cd/0x1f0
[ 683.901525] [<ffffffffc036eaae>] ? alloc_gen8_temp_bitmaps+0x2e/0x80 [i915]
[ 683.901537] [<ffffffffc036eac7>] alloc_gen8_temp_bitmaps+0x47/0x80 [i915]
[ 683.901552] [<ffffffffc036eb9c>] gen8_alloc_va_range_3lvl+0x9c/0x9f0 [i915]
[ 683.901553] [<ffffffff861b896b>] ? find_lock_entry+0x5b/0x140
[ 683.901555] [<ffffffff86411003>] ? swiotlb_map_sg_attrs+0x53/0x130
[ 683.901567] [<ffffffffc036f88c>] gen8_alloc_va_range+0x23c/0x470 [i915]
[ 683.901580] [<ffffffffc0370e5b>] i915_vma_bind+0x9b/0x180 [i915]
[ 683.901593] [<ffffffffc03774fb>] i915_gem_object_do_pin+0x86b/0xa60 [i915]
[ 683.901606] [<ffffffffc037771d>] i915_gem_object_pin+0x2d/0x30 [i915]
[ 683.901618] [<ffffffffc0365acf>] i915_gem_execbuffer_reserve_vma.isra.20+0x9f/0x180 [i915]
[ 683.901633] [<ffffffffc0365f3b>] i915_gem_execbuffer_reserve.isra.21+0x38b/0x3b0 [i915]
[ 683.901646] [<ffffffffc03671d8>] i915_gem_do_execbuffer.isra.24+0x6b8/0x1200 [i915]
[ 683.901648] [<ffffffff861b87d0>] ? find_get_entry+0x20/0x160
[ 683.901650] [<ffffffff861d9b99>] ? shmem_getpage_gfp+0xd9/0xc90
[ 683.901661] [<ffffffffc0368944>] i915_gem_execbuffer2+0x104/0x260 [i915]
[ 683.901691] [<ffffffffc0250fa0>] drm_ioctl+0x200/0x4f0 [drm]
[ 683.901704] [<ffffffffc0368840>] ? i915_gem_execbuffer+0x330/0x330 [i915]
[ 683.901705] [<ffffffff862692ff>] ? dput+0x21f/0x260
[ 683.901707] [<ffffffff86264cd3>] do_vfs_ioctl+0xa3/0x5f0
[ 683.901708] [<ffffffff86265299>] SyS_ioctl+0x79/0x90
[ 683.901710] [<ffffffff868027b2>] entry_SYSCALL_64_fastpath+0x1a/0xa4
[ 683.901711] Mem-Info:
[ 683.901714] active_anon:95440 inactive_anon:114637 isolated_anon:0
active_file:1284097 inactive_file:231741 isolated_file:0
unevictable:31 dirty:107 writeback:155137 unstable:0
slab_reclaimable:34416 slab_unreclaimable:15787
mapped:1373800 shmem:49734 pagetables:32919 bounce:0
free:26810 free_pcp:0 free_cma:0
[ 683.901717] Node 0 active_anon:381760kB inactive_anon:458548kB active_file:5136388kB inactive_file:926964kB unevictable:124kB isolated(anon):0kB isolated(file):0kB mapped:5495200kB dirty:428kB writeback:620548kB shmem:0kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 198936kB writeback_tmp:0kB unstable:0kB pages_scanned:0 all_unreclaimable? no
[ 683.901718] Node 0 DMA free:15872kB min:132kB low:164kB high:196kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15980kB managed:15896kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:24kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[ 683.901720] lowmem_reserve[]: 0 1829 7809 7809 7809
[ 683.901723] Node 0 DMA32 free:39676kB min:15796kB low:19744kB high:23692kB active_anon:2196kB inactive_anon:180kB active_file:1467288kB inactive_file:152024kB unevictable:0kB writepending:120700kB present:1958284kB managed:1892644kB mlocked:0kB slab_reclaimable:34852kB slab_unreclaimable:4228kB kernel_stack:32kB pagetables:27600kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[ 683.901725] lowmem_reserve[]: 0 0 5980 5980 5980
[ 683.901727] Node 0 Normal free:51692kB min:51648kB low:64560kB high:77472kB active_anon:379564kB inactive_anon:458368kB active_file:3669100kB inactive_file:774940kB unevictable:124kB writepending:500276kB present:6275072kB managed:6128020kB mlocked:124kB slab_reclaimable:102812kB slab_unreclaimable:58896kB kernel_stack:8288kB pagetables:104076kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[ 683.901729] lowmem_reserve[]: 0 0 0 0 0
[ 683.901731] Node 0 DMA: 0*4kB 0*8kB 2*16kB (U) 1*32kB (U) 3*64kB (U) 2*128kB (U) 0*256kB 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15872kB
[ 683.901738] Node 0 DMA32: 6599*4kB (UME) 1573*8kB (UM) 51*16kB (UM) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 39796kB
[ 683.901744] Node 0 Normal: 11012*4kB (UMEH) 955*8kB (UMH) 11*16kB (H) 1*32kB (H) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 51896kB
[ 683.901750] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
[ 683.901751] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[ 683.901752] 1565598 total pagecache pages
[ 683.901752] 0 pages in swap cache
[ 683.901753] Swap cache stats: add 0, delete 0, find 0/0
[ 683.901754] Free swap = 8126460kB
[ 683.901754] Total swap = 8126460kB
[ 683.901754] 2062334 pages RAM
[ 683.901755] 0 pages HighMem/MovableOnly
[ 683.901755] 53194 pages reserved
[ 683.901755] 0 pages cma reserved
[ 683.901756] 0 pages hwpoisoned
[ 683.901756] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
[ 683.901771] [ 771] 0 771 19588 1983 34 3 0 0 systemd-journal
[ 683.901773] [ 802] 0 802 32268 1616 29 3 0 0 lvmetad
[ 683.901775] [ 808] 0 808 11972 1901 25 3 0 -1000 systemd-udevd
[ 683.901778] [ 987] 0 987 13888 834 27 3 0 -1000 auditd
[ 683.901779] [ 998] 0 998 21136 443 12 3 0 0 audispd
[ 683.901781] [ 1001] 0 1001 10907 520 26 3 0 0 sedispatch
[ 683.901782] [ 1011] 0 1011 1104 180 8 3 0 0 rngd
[ 683.901783] [ 1012] 0 1012 4220 343 13 3 0 0 alsactl
[ 683.901784] [ 1013] 0 1013 98858 1754 45 3 0 0 accounts-daemon
[ 683.901785] [ 1015] 0 1015 10882 1188 23 3 0 0 bluetoothd
[ 683.901786] [ 1017] 0 1017 104437 2240 73 4 0 0 ModemManager
[ 683.901787] [ 1018] 172 1018 46710 823 28 3 0 0 rtkit-daemon
[ 683.901788] [ 1020] 0 1020 1642 478 9 3 0 0 mcelog
[ 683.901790] [ 1022] 81 1022 14507 1493 27 3 0 -900 dbus-daemon
[ 683.901791] [ 1026] 990 1026 28014 782 25 3 0 0 chronyd
[ 683.901792] [ 1036] 0 1036 51991 804 38 3 0 0 gssproxy
[ 683.901794] [ 1048] 0 1048 167266 8834 105 4 0 0 firewalld
[ 683.901795] [ 1050] 0 1050 12558 1987 28 3 0 0 systemd-logind
[ 683.901797] [ 1052] 70 1052 12579 990 28 3 0 0 avahi-daemon
[ 683.901798] [ 1057] 995 1057 133403 3831 56 3 0 0 polkitd
[ 683.901799] [ 1059] 0 1059 111734 2268 64 3 0 0 abrtd
[ 683.901800] [ 1066] 70 1066 12547 89 27 3 0 0 avahi-daemon
[ 683.901801] [ 1086] 0 1086 156436 3838 85 3 0 0 NetworkManager
[ 683.901802] [ 1110] 0 1110 228634 8292 174 4 0 0 libvirtd
[ 683.901803] [ 1122] 0 1122 102461 2029 47 3 0 0 gdm
[ 683.901804] [ 1125] 0 1125 33234 810 19 3 0 0 crond
[ 683.901805] [ 1126] 0 1126 6490 534 19 3 0 0 atd
[ 683.901806] [ 1213] 0 1213 93009 2339 67 4 0 0 gdm-session-wor
[ 683.901807] [ 1222] 0 1222 16576 1873 36 3 0 0 wpa_supplicant
[ 683.901808] [ 1236] 42 1236 16516 1785 36 3 0 0 systemd
[ 683.901809] [ 1238] 42 1238 24758 780 47 3 0 0 (sd-pam)
[ 683.901810] [ 1242] 42 1242 112470 2665 94 3 0 0 gdm-wayland-ses
[ 683.901811] [ 1244] 42 1244 14131 1121 28 3 0 0 dbus-daemon
[ 683.901812] [ 1247] 42 1247 172808 3320 110 4 0 0 gnome-session-b
[ 683.901813] [ 1255] 42 1255 403569 27848 305 5 0 0 gnome-shell
[ 683.901814] [ 1270] 0 1270 107218 2323 53 4 0 0 upowerd
[ 683.901816] [ 1277] 0 1277 261220 3428 344 4 0 0 abrt-dump-journ
[ 683.901817] [ 1279] 0 1279 262477 3538 345 4 0 0 abrt-dump-journ
[ 683.901818] [ 1338] 99 1338 12274 92 26 3 0 0 dnsmasq
[ 683.901819] [ 1339] 0 1339 12267 92 26 3 0 0 dnsmasq
[ 683.901820] [ 1420] 42 1420 62218 11072 107 3 0 0 Xwayland
[ 683.901822] [ 1426] 42 1426 86174 1417 36 3 0 0 at-spi-bus-laun
[ 683.901823] [ 1431] 42 1431 14074 920 27 3 0 0 dbus-daemon
[ 683.901824] [ 1434] 42 1434 55841 1513 42 4 0 0 at-spi2-registr
[ 683.901825] [ 1440] 42 1440 164934 2682 84 4 0 0 pulseaudio
[ 683.901826] [ 1453] 42 1453 115040 2138 39 3 0 0 ibus-daemon
[ 683.901827] [ 1456] 42 1456 95634 1424 38 3 0 0 ibus-dconf
[ 683.901828] [ 1459] 42 1459 126126 6717 129 3 0 0 ibus-x11
[ 683.901829] [ 1465] 42 1465 109804 2173 59 3 0 0 xdg-permission-
[ 683.901830] [ 1473] 0 1473 196027 18444 150 3 0 0 packagekitd
[ 683.901831] [ 1477] 42 1477 302617 9107 200 5 0 0 gnome-settings-
[ 683.901832] [ 1497] 42 1497 77184 1362 34 3 0 0 ibus-engine-sim
[ 683.901833] [ 1538] 993 1538 103715 2539 54 3 0 0 colord
[ 683.901834] [ 1583] 0 1583 98709 2395 77 3 0 0 gdm-session-wor
[ 683.901835] [ 1592] 0 1592 21780 4717 46 3 0 0 dhclient
[ 683.901836] [ 1641] 0 1641 84698 2398 50 4 0 0 nm-openvpn-serv
[ 683.901837] [ 1645] 988 1645 17970 1854 40 3 0 0 openvpn
[ 683.901838] [ 1648] 1000 1648 16517 1756 34 4 0 0 systemd
[ 683.901839] [ 1656] 1000 1656 24794 801 47 3 0 0 (sd-pam)
[ 683.901840] [ 1666] 1000 1666 118117 2041 44 3 0 0 gnome-keyring-d
[ 683.901841] [ 1669] 1000 1669 112470 2807 97 3 0 0 gdm-wayland-ses
[ 683.901843] [ 1671] 1000 1671 14340 1294 30 3 0 0 dbus-daemon
[ 683.901844] [ 1674] 1000 1674 172877 3440 114 4 0 0 gnome-session-b
[ 683.901845] [ 1686] 1000 1686 98759 1747 42 3 0 0 gvfsd
[ 683.901846] [ 1691] 1000 1691 104451 1327 37 3 0 0 gvfsd-fuse
[ 683.901847] [ 1714] 1000 1714 447111 39711 335 5 0 0 gnome-shell
[ 683.901848] [ 1729] 1000 1729 62884 11611 111 3 0 0 Xwayland
[ 683.901849] [ 1735] 1000 1735 86177 1474 36 4 0 0 at-spi-bus-laun
[ 683.901850] [ 1740] 1000 1740 14106 1108 29 3 0 0 dbus-daemon
[ 683.901851] [ 1743] 1000 1743 55841 1516 46 3 0 0 at-spi2-registr
[ 683.901852] [ 1749] 1000 1749 173283 3029 102 4 0 0 pulseaudio
[ 683.901853] [ 1765] 1000 1765 221322 8359 193 4 0 0 gnome-shell-cal
[ 683.901854] [ 1766] 1000 1766 115001 2100 41 4 0 0 ibus-daemon
[ 683.901855] [ 1770] 1000 1770 95645 1397 37 3 0 0 ibus-dconf
[ 683.901855] [ 1772] 1000 1772 126126 6529 126 4 0 0 ibus-x11
[ 683.901856] [ 1782] 1000 1782 229523 9384 213 4 0 0 evolution-sourc
[ 683.901857] [ 1785] 1000 1785 109804 2197 62 4 0 0 xdg-permission-
[ 683.901858] [ 1794] 1000 1794 105580 2119 55 3 0 0 gvfs-udisks2-vo
[ 683.901859] [ 1801] 0 1801 97029 2083 54 3 0 0 udisksd
[ 683.901860] [ 1808] 1000 1808 222729 7688 172 4 0 0 goa-daemon
[ 683.901861] [ 1811] 1000 1811 98629 1391 40 3 0 0 gvfs-gphoto2-vo
[ 683.901862] [ 1817] 1000 1817 94552 1372 35 3 0 0 gvfs-goa-volume
[ 683.901864] [ 1827] 1000 1827 136872 2734 108 3 0 0 goa-identity-se
[ 683.901865] [ 1829] 1000 1829 96354 1300 38 3 0 0 gvfs-mtp-volume
[ 683.901866] [ 1836] 1000 1836 122361 2095 53 4 0 0 gvfs-afc-volume
[ 683.901867] [ 1848] 1000 1848 322422 10974 240 5 0 0 gnome-settings-
[ 683.901868] [ 1861] 1000 1861 269205 10731 229 4 0 0 evolution-calen
[ 683.901870] [ 1889] 1000 1889 77225 1429 35 3 0 0 ibus-engine-sim
[ 683.901871] [ 1981] 1000 1981 290746 9893 206 4 0 0 evolution-calen
[ 683.901872] [ 1993] 1000 1993 163552 5140 89 4 0 0 tracker-miner-f
[ 683.901873] [ 1995] 1000 1995 158399 4233 78 4 0 0 tracker-miner-a
[ 683.901874] [ 1999] 1000 1999 185785 4846 96 4 0 0 tracker-extract
[ 683.901875] [ 2010] 1000 2010 140701 4027 79 4 0 0 tracker-miner-u
[ 683.901876] [ 2011] 0 2011 52365 1984 53 3 0 0 cupsd
[ 683.901878] [ 2017] 1000 2017 46916 1268 27 4 0 0 dconf-service
[ 683.901879] [ 2021] 1000 2021 265817 9429 221 4 0 0 evolution-addre
[ 683.901880] [ 2023] 1000 2023 272624 9896 198 4 0 0 evolution-calen
[ 683.901881] [ 2027] 1000 2027 133874 3898 60 4 0 0 tracker-store
[ 683.901882] [ 2043] 1000 2043 160491 3462 122 4 0 0 gsd-printer
[ 683.901883] [ 2051] 1000 2051 168185 6168 137 3 0 0 abrt-applet
[ 683.901884] [ 2054] 1000 2054 83177 4194 112 3 0 0 seapplet
[ 683.901885] [ 2071] 1000 2071 308067 9309 203 4 0 0 evolution-addre
[ 683.901886] [ 2127] 1000 2127 657040 48104 313 6 0 0 insync
[ 683.901887] [ 2133] 0 2133 85913 2519 64 4 0 -900 abrt-dbus
[ 683.901888] [ 2163] 1000 2163 45120 1422 39 3 0 0 gconfd-2
[ 683.901890] [ 2200] 1000 2200 77445 1596 35 4 0 0 gvfsd-metadata
[ 683.901891] [ 2215] 1000 2215 203657 11515 145 4 0 0 gnome-terminal-
[ 683.901892] [ 2235] 1000 2235 117765 1710 47 3 0 0 gvfsd-trash
[ 683.901893] [ 2309] 1000 2309 30789 1208 15 3 0 0 bash
[ 683.901895] [ 2397] 1000 2397 170605 13763 148 4 0 0 gnome-system-mo
[ 683.901896] [ 3036] 1000 3036 12251152 1306699 23712 50 0 0 SyrenProcessor_
[ 683.901897] [ 3042] 1000 3042 30763 1084 14 3 0 0 bash
[ 683.901899] [ 3122] 1000 3122 30267 247 12 3 0 0 dmesg
[ 683.901900] Out of memory: Kill process 3036 (SyrenProcessor_) score 329 or sacrifice child
[ 683.901928] Killed process 3036 (SyrenProcessor_) total-vm:49004608kB, anon-rss:1368kB, file-rss:5226416kB, shmem-rss:0kB
正如您所看到的，我的应用程序在内存映射中保存了约 50GB。
我的假设是，当我的应用程序访问虚拟地址空间中的数据时，Linux 会计算出该地址位于哪个页面，如果它不在 RAM 中，则触发页面错误以从磁盘中提取该页面。在这种假设下，RAM 中的页面数量与访问内存映射的线程数量相同 - 我知道实际上 Linux 会缓存尽可能多的页面以提高性能，但 Linux 应该根据需要丢弃较少的活动页面，因此它们不应该'这不是问题。这就是为什么我认为使用内存映射时不会出现 OOM 错误（假设您有磁盘空间并且不超过 64 位地址范围）。显然情况并非如此，所以有人可以纠正我的假设吗？
最后一行anon-rss:1368kB似乎是合理的，因为我的应用程序使用很少的 RAM 来实现它自己的功能，并且file-rss:5226416kB表明它正在尝试将 5.2 GB 的内存映射数据放入 RAM - 并且本来就有那么多可用的内存。
那么为什么会触发OOM呢？
答案1
Linux 允许过度分配内存，因为大多数程序要求的内存多于实际需要的内存，然后当它找到内存时就会担心有实际上过度分配了内存并启动了 OOM 杀手。
sysctl vm.overcommit_memory 可能会有所帮助，将其设置为 2 会导致操作系统在您执行操作系统无法处理的操作时给出错误，而不是希望得到最好的结果。
拥有足够大的交换分区/文件来保存数据可能会让事情按预期工作。
或者，这可能是文件本身太大的问题，因此 mmap2() 可能是更好的选择。