RFC4638 (PPPoE MTU > 1492) + SQM Causing Out of Memory

4zims · December 20, 2024, 11:11am

While testing RFC4638 to increase the MTU beyond 1492 with SQM enabled, I found that it occasionally results in out of memory issues.

root@OpenWrt:~# ubus call system board
{
        "kernel": "6.6.65",
        "hostname": "OpenWrt",
        "system": "MediaTek MT7621 ver:1 eco:3",
        "model": "D-Link DIR-882 A1",
        "board_name": "dlink,dir-882-a1",
        "rootfs_type": "squashfs",
        "release": {
                "distribution": "OpenWrt",
                "version": "24.10-SNAPSHOT",
                "revision": "r28195-f0ff244c69",
                "target": "ramips/mt7621",
                "description": "OpenWrt 24.10-SNAPSHOT r28195-f0ff244c69",
                "builddate": "1734522470"
        }
}

cat /etc/config/sqm

config queue 'eth1'
        option enabled '1'
        option interface 'pppoe-wan'
        option download '95000'
        option upload '50000'
        option qdisc 'fq_codel'
        option script 'simplest_tbf.qos'
        option linklayer 'ethernet'
        option debug_logging '0'
        option verbosity '5'
        option overhead '44'
        option linklayer_advanced '1'
        option tcMTU '2047'
        option tcTSIZE '128'
        option tcMPU '84'
        option linklayer_adaptation_mechanism 'default'

cat /etc/config/network

config interface 'loopback'
        option device 'lo'
        option proto 'static'
        option ipaddr '127.0.0.1'
        option netmask '255.0.0.0'

config globals 'globals'
        option packet_steering '1'

config device
        option name 'br-lan'
        option type 'bridge'
        list ports 'lan1'
        list ports 'lan2'
        list ports 'lan3'
        list ports 'lan4'

config interface 'lan'
        option device 'br-lan'
        option proto 'static'
        option ipaddr '192.168.0.1'
        option netmask '255.255.255.0'
        option ip6assign '64'
        option hostname 'OpenWrt'
        option delegate '0'

config interface 'wan'
        option device 'wan.500'
        option proto 'pppoe'
        option username '*****************'
        option password '******************'
        option ipv6 '1'
        list dns '1.1.1.1'
        list dns '1.0.0.1'
        option peerdns '0'
        option metric '4'
        option keepalive '0 1'
        option delegate '0'

config interface 'wan6'
        option device '@wan'
        option proto 'dhcpv6'
        list dns '2606:4700:4700::1111'
        list dns '2606:4700:4700::1001'
        option peerdns '0'
        option metric '5'
        option reqaddress 'none'
        option reqprefix 'auto'
        option norelease '1'

config device
        option name 'eth0'
        option mtu '1508'

config device
        option name 'pppoe-wan'
        option mtu '1500'

root@OpenWrt:~# logread | grep kern

Fri Dec 20 18:27:45 2024 kern.info kernel: [46039.802506] ash (9499): drop_caches: 3
Fri Dec 20 18:27:48 2024 kern.info kernel: [46043.079521] ash (9499): drop_caches: 3
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.712075] napi/mtk_eth-6: page allocation failure: order:0, mode:0x820(GFP_ATOMIC), nodemask=(null),cpuset=/,mems_allowed=0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.734858] CPU: 0 PID: 283 Comm: napi/mtk_eth-6 Tainted: G           O       6.6.65 #0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.750863] Stack : 00000000 0000011b 00000820 8008a114 00000000 00000000 00000000 00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.767654]         00000000 00000000 00000000 00000000 00000000 00000001 81d27b80 818412c0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.784386]         81d27c18 00000000 00000000 81d27ac0 00000038 80822dc4 ffffffea 00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.801088]         81d27acc 00000543 8094d060 ffffffff 80841a38 81d27b60 00000000 00000830
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.817784]         00000820 00000820 00000820 80945440 00000018 80496ad4 00000000 80b10000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.834484]         ...
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.839354] Call Trace:
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.839367] [<8008a114>] 0x8008a114
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.851443] [<80822dc4>] 0x80822dc4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.858509] [<80496ad4>] 0x80496ad4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.865585] [<800073b8>] 0x800073b8
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.872532] [<800073c0>] 0x800073c0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.879473] [<807f8f9c>] 0x807f8f9c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.886415] [<800ea098>] 0x800ea098
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.893420] [<801cf5ac>] 0x801cf5ac
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.900594] [<801d0418>] 0x801d0418
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.907537] [<805b2f60>] 0x805b2f60
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.914605] [<805f8704>] 0x805f8704
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.921546] [<8001d594>] 0x8001d594
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.928609] [<801d0ddc>] 0x801d0ddc
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.935554] [<80596e2c>] 0x80596e2c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.942617] [<8054e268>] 0x8054e268
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.949556] [<800c9b6c>] 0x800c9b6c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.956854] [<8006978c>] 0x8006978c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.964093] [<805bdfb0>] 0x805bdfb0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.971092] [<808248fc>] 0x808248fc
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.978150] [<805be314>] 0x805be314
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.985211] [<805be298>] 0x805be298
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.992323] [<805be364>] 0x805be364
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47560.999321] [<800535c4>] 0x800535c4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.006264] [<805be3f0>] 0x805be3f0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.013265] [<80825080>] 0x80825080
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.020377] [<800536c8>] 0x800536c8
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.027315] [<800535c4>] 0x800535c4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.034433] [<800535c4>] 0x800535c4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.041488] [<80002a58>] 0x80002a58
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.048457]
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.051506] Mem-Info:
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072] active_anon:668 inactive_anon:643 isolated_anon:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072]  active_file:140 inactive_file:453 isolated_file:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072]  unevictable:0 dirty:0 writeback:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072]  slab_reclaimable:599 slab_unreclaimable:5410
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072]  mapped:444 shmem:339 pagetables:109
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072]  sec_pagetables:0 bounce:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072]  kernel_misc_reclaimable:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.056072]  free:4150 free_pcp:25 free_cma:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.131389] Node 0 active_anon:2672kB inactive_anon:2572kB active_file:832kB inactive_file:1468kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1776kB dirty:0kB writeback:0kB shmem:1356kB writeback_tmp:0kB kernel_stack:848kB pagetables:436kB sec_pagetables:0kB all_unreclaimable? no
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.132081] logd invoked oom-killer: gfp_mask=0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), order=0, oom_score_adj=0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.183699] Normal free:17104kB boost:0kB min:16384kB low:20480kB high:24576kB reserved_highatomic:0KB active_anon:2672kB inactive_anon:2572kB active_file:272kB inactive_file:1528kB unevictable:0kB writepending:0kB present:131072kB managed:119268kB mlocked:0kB bounce:0kB free_pcp:104kB local_pcp:0kB free_cma:0kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.183758] lowmem_reserve[]: 0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.204201] CPU: 2 PID: 8305 Comm: logd Tainted: G           O       6.6.65 #0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.259165]  0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.265384] Stack : 00000000 00002071
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.279769]
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.283051]  809d0148
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.290334] Normal:
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.293266]  8008a114 00000000 00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.297786] 235*4kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.302111]  00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.309737] (UME)
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.314052]  00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.314068]         00000000 00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.318580] 104*8kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.322564]  00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.327078] (UM)
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.334331]  00000000 00000000 00000001
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.338675] 283*16kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.343178]  84523b88 8188e400
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.347003] (UM)
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.354617]         84523c20 00000000
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.359136] 186*32kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.365196]  00000000 00000125 00000038 80822dc4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.369030] (UM)
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.376300]  00000008 0000093e
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.376320]
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.380818] 31*64kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.389987]  84523974 84523981 ffffffff
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.393826] (UM)
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.399873]  ffffffff
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.404044] 19*128kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.408360]  80841a38
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.415990] (U)
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.419786]  84523b68
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.424302] 0*256kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.428791]  8188b200
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.433305] 2*512kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.436930]  00000840
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.441429] (UM) 0*1024kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.445759]
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.445765]         00000000 00140cca
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.450276] 0*2048kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.454606]  809d0148 80945440 00000018
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.459123] 0*4096kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.464491]  80496ad4 00000008 80b10008
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.467463] 0*8192kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.474731]         ...
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.474748] Call Trace:
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.479249] = 17692kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.479256] 751 total pagecache pages
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.486871] [<8008a114>] 0x8008a114
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.491384] 0 pages in swap cache
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.491390] Free swap  = 0kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.499224] [<80822dc4>] 0x80822dc4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.503530] Total swap = 0kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.508603] [<80496ad4>] 0x80496ad4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.513234] 32768 pages RAM
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.517843] [<800073b8>] 0x800073b8
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.525002] 0 pages HighMem/MovableOnly
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.531914] [<800073c0>] 0x800073c0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.538500] 2951 pages reserved
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.544200] [<807f8f9c>] 0x807f8f9c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.544336] [<801765dc>] 0x801765dc
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.611246] [<80176ef4>] 0x80176ef4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.618267] [<8017726c>] 0x8017726c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.625272] [<8017748c>] 0x8017748c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.632217] [<801cfff8>] 0x801cfff8
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.639424] [<80172ac0>] 0x80172ac0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.647003] [<80173354>] 0x80173354
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.653952] [<80170888>] 0x80170888
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.661320] [<801ae55c>] 0x801ae55c
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.668380] [<801b4bbc>] 0x801b4bbc
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.675395] [<80065bc4>] 0x80065bc4
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.682804] [<800166c8>] 0x800166c8
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.689922] [<8001b9a8>] 0x8001b9a8
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.697016]
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.705918] Mem-Info:
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549] active_anon:643 inactive_anon:668 isolated_anon:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549]  active_file:147 inactive_file:156 isolated_file:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549]  unevictable:0 dirty:0 writeback:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549]  slab_reclaimable:599 slab_unreclaimable:5410
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549]  mapped:368 shmem:339 pagetables:109
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549]  sec_pagetables:0 bounce:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549]  kernel_misc_reclaimable:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.713549]  free:4341 free_pcp:41 free_cma:0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.789324] Node 0 active_anon:2572kB inactive_anon:2672kB active_file:588kB inactive_file:624kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1472kB dirty:0kB writeback:0kB shmem:1356kB writeback_tmp:0kB kernel_stack:848kB pagetables:436kB sec_pagetables:0kB all_unreclaimable? no
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.843565] Normal free:17364kB boost:0kB min:16384kB low:20480kB high:24576kB reserved_highatomic:0KB active_anon:2572kB inactive_anon:2672kB active_file:400kB inactive_file:1136kB unevictable:0kB writepending:0kB present:131072kB managed:119268kB mlocked:0kB bounce:0kB free_pcp:156kB local_pcp:0kB free_cma:0kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.915496] lowmem_reserve[]: 0 0
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.922170] Normal: 348*4kB (ME) 430*8kB (UM) 284*16kB (UM) 76*32kB (UM) 31*64kB (UM) 29*128kB (U) 1*256kB (U) 2*512kB (UM) 0*1024kB 0*2048kB 0*4096kB 0*8192kB = 18784kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.955632] 417 total pagecache pages
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.962945] 0 pages in swap cache
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.970083] Free swap  = 0kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.979072] Total swap = 0kB
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.985872] 32768 pages RAM
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47561.994970] 0 pages HighMem/MovableOnly
Fri Dec 20 18:53:08 2024 kern.warn kernel: [47562.005074] 2951 pages reserved
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.015655] Tasks state (memory values in pages):
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.025707] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.046287] [    690]    81   690      385       96    20480       32             0 ubusd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.063033] [    691]     0   691      272        0    20480        0             0 askfirst
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.083123] [    726]     0   726      310        0    12288        0             0 urngd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.102824] [   1456]     0  1456      326       32    16384        0             0 dropbear
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.120416] [   1625]     0  1625      689       32    24576        0             0 netifd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.139599] [   1745]     0  1745      476       32    20480        0             0 odhcpd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.156345] [   2818]     0  2818      735        0    20480        0             0 ntpd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.173847] [   2869]   123  2869      350        0    16384        0             0 ntpd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.192071] [   3152]     0  3152      387        0    16384       32             0 pppd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.211749] [   3585]     0  3585      312       96    20480        0             0 odhcp6c
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.231436] [   4075]     0  4075      735       63    16384        0             0 dnsmasq
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.248532] [   4102]   453  4102      475       64    16384        0             0 dnsmasq
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.267625] [   5708]     0  5708      735       32    20480        0             0 wpa_supplicant
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.285720] [   5709]   101  5709     1174       96    20480       64             0 wpa_supplicant
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.305275] [   8305]   514  8305      588        0    16384       32             0 logd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.322149] [   8306]     0  8306      941      128    24576       32             0 rpcd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.341348] [   8314]     0  8314      735        0    20480        0             0 hostapd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.361048] [   8317]   101  8317     1257      126    24576        0             0 hostapd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.379680] [   8323]     0  8323      507       64    20480        0             0 uhttpd
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.400767] [   9609]     0  9609      331       32    20480        0             0 dropbear
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.418024] [   9610]     0  9610      351       32    20480        0             0 ash
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.437062] [   9994]     0  9994      423        0    16384        0             0 logread
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.456358] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/,task=hostapd,pid=8317,uid=101
Fri Dec 20 18:53:08 2024 kern.err kernel: [47562.485003] Out of memory: Killed process 8317 (hostapd) total-vm:5028kB, anon-rss:504kB, file-rss:0kB, shmem-rss:0kB, UID:101 pgtables:24kB oom_score_adj:0
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.671660] br-lan: port 7(phy1-ap0.sta3) entered disabled state
Fri Dec 20 18:53:08 2024 kern.info kernel: [47562.808669] br-lan: port 6(phy1-ap0) entered disabled state
Fri Dec 20 18:53:09 2024 kern.info kernel: [47563.826938] br-lan: port 7(phy1-ap0.sta3) entered disabled state

root@OpenWrt:~# free
              total        used        free      shared  buff/cache   available
Mem:         119268       60856       43392        1396       15020       25632
Swap:             0           0           0
r

frollic · December 20, 2024, 11:15am

OK, and ... ?

wilsonyan · December 20, 2024, 12:18pm

Hmm, not sure what you're doing, you don't appear to be using this with a dsl device so you'd need to make sure you've set everything correctly and have a device that supports the mini-jumbo mtu

It seems like the mt7621 should support an mtu of 1508 though it looks like going over 1500 is a little off script. I'm not sure but you might need to make sure you've set the higher mtu (1508) for every device in the chain that the pppoe interface will be running off i.e eth0 ? eth1 ? wan ? etc etc you can't just set the mtu to 1500 for the pppoe sorry if you already know this. It's possible though that the mt7621 just isn't capable to use an mtu over 1500 with hardware acceleration or something.

4zims · December 20, 2024, 2:23pm

It's connected to a fiber, and I'm not using hardware offload with SQM.

The MTU appears to be 1500 here:

root@OpenWrt:~# ifconfig
br-lan    Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          inet addr:192.168.0.1  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::XXXX:XXXX:XXXX:XXXX/64 Scope:Link
          inet6 addr: XXXX:XXXX:XXXX:XXXX::1/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2957768 errors:0 dropped:12 overruns:0 frame:0
          TX packets:12373417 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:454621016 (433.5 MiB)  TX bytes:16334566827 (15.2 GiB)

ifb4pppoe-wan Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          inet6 addr: fe80::XXXX:XXXX:XXXX:XXXX/64 Scope:Link
          UP BROADCAST RUNNING NOARP  MTU:1500  Metric:1
          RX packets:5218 errors:0 dropped:2 overruns:0 frame:0
          TX packets:5216 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:32
          RX bytes:6339469 (6.0 MiB)  TX bytes:6339329 (6.0 MiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:11440 errors:0 dropped:0 overruns:0 frame:0
          TX packets:11440 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1372221 (1.3 MiB)  TX bytes:1372221 (1.3 MiB)

phy0-ap0  Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:929486 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2411528 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:152791969 (145.7 MiB)  TX bytes:3318076713 (3.0 GiB)

phy1-ap0  Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:455132 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1087537 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:125342236 (119.5 MiB)  TX bytes:1260656274 (1.1 GiB)

phy1-ap0.sta2 Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1818006 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8506918 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:232833110 (222.0 MiB)  TX bytes:12008445371 (11.1 GiB)

pppoe-wan Link encap:Point-to-Point Protocol
          inet addr:XXX.XXX.XXX.XXX  P-t-P:XXX.XXX.XXX.XXX  Mask:255.255.255.255
          inet6 addr: fe80::XXXX:XXXX:XXXX:XXXX/128 Scope:Link
          inet6 addr: XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX/64 Scope:Global
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:12417552 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3187225 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:16239341292 (15.1 GiB)  TX bytes:463021092 (441.5 MiB)

wan       Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          inet6 addr: fe80::XXXX:XXXX:XXXX:XXXX/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:56568068 errors:0 dropped:60438 overruns:0 frame:0
          TX packets:16617101 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:61295306424 (57.0 GiB)  TX bytes:3136831834 (2.9 GiB)
          Interrupt:19

wan.500   Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          inet6 addr: fe80::XXXX:XXXX:XXXX:XXXX/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:56505252 errors:0 dropped:0 overruns:0 frame:0
          TX packets:16618412 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:60226817386 (56.0 GiB)  TX bytes:3003913517 (2.7 GiB)

I'm not sure why this causes an out of memory. Increasing the MTU by 8 bytes shouldn't be that much, no?

wilsonyan · December 20, 2024, 2:39pm

Probably has nothing to do with it:

github.com/openwrt/openwrt

kernel: generic: patch: 802.2+LLC - set transport_header offset

openwrt:main ← APCCV:main

opened 08:45PM - 09 Dec 24 UTC

APCCV

+48 -0

With the introduction of DSA, network_header and transport_header offsets in skb… for 802.2+LLC packets are short by two bytes when pulled out of the backlog. This issue is caused by DSA as it appears after applying the commmit that converts an architecture to DSA. skb buffer is processed without issue through GRO (if active), netif_receive and br_handle_frame as none of it relies on the offsets. Once skb processing reaches __netif_receive_skb_one_core, code resets network_header offset but assumes transport_header is accurate (if set), leaving it untouched. For 802.2+LLC+SNAP frames this causes an issue as llc_rcv assumes the offset as correct and advances transport_header offset to denote the SNAP header location. Once skb processing reaches snap_rcv for handling, SNAP header is misaligned by two, failing match with registered handlers, and packet is silently dropped. Patch modifies llc_rcv to reset transport_header offset and apply the LLC header size increment, instead of applying the increment on existing value. This allows snap_rcv to match OUI:PID values properly and restores normal behaviour. An additional benefit would be that any non SNAP 802.2+LLC processing will now receive an accurate transport_header offset, although this code and 802.2+LLC supported protocols are very mature so if no other issues have been noticed already, odds are none will. Issue does not apply to for Ethernet II frames supporting IPv4/v6 traffic as that stack most probably resets transport_header before using it (if it does at all). Regardless, this patch does not affect Ethernet II frame processing as Ethernet II frames are never handled by llc_rcv(). Patch and comments set to netdev@vger.kernel.org for feedback. Tested successfully: - on ipq806x (C2600) and ath79 (DIR-835). - on snapshot and (although redundant but just in case) 23.05. Discussion here: https://forum.openwrt.org/t/dsa-and-appletalk-multicast-issues/216494/102 Open issue here: https://github.com/openwrt/openwrt/issues/17095

brada4 · December 20, 2024, 2:41pm

This is documented as:

Because of this, use outside of a testing or debugging environment is not recommended

.

wilsonyan · December 20, 2024, 2:47pm

What device is the pppoe interface running off ?

Your wan and wan.500 are only mtu 1500, if that's what the pppoe is running off they need to be 1508

4zims · January 4, 2025, 4:50pm

Apparently, although it works, setting eth0 MTU to 1508 is what causes the OOM error.
Now no more OOM error after I changed it to this:

config device
        option name 'wan'
        option mtu '1508'

config device
        option name 'pppoe-wan'
        option mtu '1500'

system · January 14, 2025, 4:50pm

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