O Linux não está desistindo da memória armazenada em cache

Question

Estou executando uma compilação yocto com o kernel 4.4.91 em um dispositivo embarcado com 256MB de RAM, sem troca.

Estou tentando baixar um arquivo grande para mmc flash por meio do comando tftp, durante o qual, de acordo com / proc / meminfo, meu cache cresce e a memória livre cai para zero, acionando problemas de alocação de memória e watchdog que está configurado para reinicializar máquina, uma vez que o espaço livre desce para 4mb.

Eu tentei ajustar a pressão do cache, os ajustes verificados da memória do kernel estão definidos como padrão e correspondem ao mesmo dispositivo que está executando uma compilação mais antiga.

Eu não vi esse problema rodando uma versão antiga do yocto com o kernel 3.12.10.

O que mais eu posso tentar forçar o kernel a desistir da memória cache, e que outros ajustes eu posso experimentar?

Aqui está uma mensagem de amostra. Eu suspeito que tenha algo a ver com o lowmem_reserve e o número de páginas no highmem.

[ 2471.077819] CPU: 0 PID: 1279 Comm: mmcqd/0 Tainted: G           O    4.4.91-g2657e61db2 #3
[ 2471.086520] Hardware name: Generic AM33XX (Flattened Device Tree)
[ 2471.092936] Backtrace: 
[ 2471.095550] [<c0019608>] (dump_backtrace) from [<c0019804>] (show_stack+0x18/0x1c)
[ 2471.103520]  r7:00000002 r6:00000000 r5:00000002 r4:02284020
[ 2471.109519] [<c00197ec>] (show_stack) from [<c02892c0>] (dump_stack+0x24/0x28)
[ 2471.117135] [<c028929c>] (dump_stack) from [<c00adc0c>] (warn_alloc_failed+0xe4/0x124)
[ 2471.125483] [<c00adb2c>] (warn_alloc_failed) from [<c00b0d4c>] (__alloc_pages_nodemask+0x814/0x9a4)
[ 2471.135005]  r3:00000000 r2:00000000
[ 2471.138775]  r6:cd0012c0 r5:dcfdcfdd r4:00000000
[ 2471.143662] [<c00b0538>] (__alloc_pages_nodemask) from [<c00da04c>] (cache_alloc_refill+0x2c0/0x514)
[ 2471.153279]  r10:00000000 r9:02088020 r8:00000000 r7:cd0012c0 r6:cd0012c0 r5:cd0004c0
[ 2471.161547]  r4:00000000
[ 2471.164222] [<c00d9d8c>] (cache_alloc_refill) from [<c00da538>] (__kmalloc+0xcc/0xf4)
[ 2471.172466]  r10:cd60d3a0 r9:cd170218 r8:00000001 r7:400e0013 r6:cd0004c0 r5:cd60c000
[ 2471.180737]  r4:02088020
[ 2471.183421] [<c00da46c>] (__kmalloc) from [<c0301728>] (edma_prep_slave_sg+0xa0/0x328)
[ 2471.191757]  r7:ffffffff r6:cd5ec148 r5:cd60c000 r4:00000000
[ 2471.197750] [<c0301688>] (edma_prep_slave_sg) from [<c04664b0>] (omap_hsmmc_request+0x454/0x618)
[ 2471.207000]  r10:cd60d3a0 r9:cd5ec208 r8:00000000 r7:ffffffff r6:cd5ec148 r5:c0301688
[ 2471.215270]  r4:cd5adc00
[ 2471.217954] [<c046605c>] (omap_hsmmc_request) from [<c044ddfc>] (__mmc_start_request+0x48/0xdc)
[ 2471.227114]  r10:cd607eac r9:00000000 r8:cd5ec148 r7:cd5ec148 r6:cd5ec148 r5:cd5adc00
[ 2471.235384]  r4:cd5ec148
[ 2471.238061] [<c044ddb4>] (__mmc_start_request) from [<c044df7c>] (mmc_start_request+0xec/0x114)
[ 2471.247219]  r9:00000000 r8:cd5ec250 r7:cd5ec148 r6:cd5ec148 r5:cd5adc00 r4:cd5ec148
[ 2471.255411] [<c044de90>] (mmc_start_request) from [<c044f2bc>] (mmc_start_req+0x29c/0x3c4)
[ 2471.264113]  r5:cd5c3c00 r4:cd5adc00
[ 2471.267904] [<c044f020>] (mmc_start_req) from [<c045e84c>] (mmc_blk_issue_rw_rq+0xc4/0xa88)
[ 2471.276697]  r10:cb4eb9d8 r9:245d0001 r8:cd5ec144 r7:cd5ec148 r6:cb4eb9d8 r5:cd5c3c00
[ 2471.284968]  r4:cd5ec004
[ 2471.287647] [<c045e788>] (mmc_blk_issue_rw_rq) from [<c045f45c>] (mmc_blk_issue_rq+0x24c/0x4e0)
[ 2471.296806]  r10:cb4eb9d8 r9:245d0001 r8:cd5ec000 r7:cd5ec000 r6:cd4f9088 r5:cd5c3c00
[ 2471.305077]  r4:cd5ec004
[ 2471.307755] [<c045f210>] (mmc_blk_issue_rq) from [<c045ff84>] (mmc_queue_thread+0xa0/0x164)
[ 2471.316547]  r10:00000000 r9:245d0001 r8:ffffe000 r7:cd5ec00c r6:cd4f9088 r5:cd606000
[ 2471.324818]  r4:cd5ec004
[ 2471.327508] [<c045fee4>] (mmc_queue_thread) from [<c0055020>] (kthread+0xf8/0x110)
[ 2471.335477]  r9:00000000 r8:c045fee4 r7:cd5ec004 r6:cd606000 r5:cd5f6e40 r4:00000000
[ 2471.343680] [<c0054f28>] (kthread) from [<c0015518>] (ret_from_fork+0x14/0x3c)
[ 2471.351284]  r8:00000000 r7:00000000 r6:00000000 r5:c0054f28 r4:cd5f6e40
[ 2471.358364] Mem-Info:
[ 2471.360774] active_anon:19476 inactive_anon:2093 isolated_anon:0
[ 2471.360774]  active_file:17499 inactive_file:13549 isolated_file:0
[ 2471.360774]  unevictable:338 dirty:2923 writeback:1337 unstable:0
[ 2471.360774]  slab_reclaimable:2493 slab_unreclaimable:3156
[ 2471.360774]  mapped:3711 shmem:2429 pagetables:277 bounce:0
[ 2471.360774]  free:2228 free_pcp:80 free_cma:676
[ 2471.396419] Normal free:8912kB min:4096kB low:5120kB high:6144kB active_anon:77904kB inactive_anon:8372kB active_file:69996kB inactive_file:54196kB unevictable:1352ko
[ 2471.445276] lowmem_reserve[]: 0 0 0
[ 2471.448963] Normal: 1584*4kB (UMC) 28*8kB (MC) 19*16kB (C) 8*32kB (C) 4*64kB (C) 4*128kB (C) 0*256kB 2*512kB (C) 0*1024kB 0*2048kB 0*4096kB 0*8192kB = 8912kB
[ 2471.463895] 33736 total pagecache pages
[ 2471.467930] 65024 pages RAM
[ 2471.470866] 0 pages HighMem/MovableOnly
[ 2471.474901] 2813 pages reserved
[ 2471.478204] 6144 pages cma reserved
[ 2471.482040] edma 49000000.edma: edma_prep_slave_sg: Failed to allocate a descriptor
[ 2471.490114] omap_hsmmc 481d8000.mmc: prep_slave_sg() failed
[ 2471.496008] omap_hsmmc 481d8000.mmc: MMC start dma failure
[ 2471.516691] mmcblk0: unknown error -1 sending read/write command, card status 0x900
[ 2471.525087] blk_update_request: I/O error, dev mmcblk0, sector 2178224
[ 2471.532013] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272279)
[ 2471.545412] Buffer I/O error on device mmcblk0p2, logical block 264454
[ 2471.552629] blk_update_request: I/O error, dev mmcblk0, sector 2178232
[ 2471.559518] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272280)
[ 2471.572931] Buffer I/O error on device mmcblk0p2, logical block 264455
[ 2471.579923] blk_update_request: I/O error, dev mmcblk0, sector 2178240
[ 2471.586837] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272281)
[ 2471.600232] Buffer I/O error on device mmcblk0p2, logical block 264456
[ 2471.607209] blk_update_request: I/O error, dev mmcblk0, sector 2178248
[ 2471.614111] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272282)
[ 2471.627508] Buffer I/O error on device mmcblk0p2, logical block 264457
[ 2471.634468] blk_update_request: I/O error, dev mmcblk0, sector 2178256
[ 2471.641351] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272283)
[ 2471.654744] Buffer I/O error on device mmcblk0p2, logical block 264458
[ 2471.661708] blk_update_request: I/O error, dev mmcblk0, sector 2178264
[ 2471.668590] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272284)
[ 2471.681985] Buffer I/O error on device mmcblk0p2, logical block 264459
[ 2471.688929] blk_update_request: I/O error, dev mmcblk0, sector 2178272
[ 2471.695829] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272285)
[ 2471.709218] Buffer I/O error on device mmcblk0p2, logical block 264460
[ 2471.716174] blk_update_request: I/O error, dev mmcblk0, sector 2178280
[ 2471.723069] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272286)
[ 2471.736467] Buffer I/O error on device mmcblk0p2, logical block 264461
[ 2471.743425] blk_update_request: I/O error, dev mmcblk0, sector 2178288
[ 2471.750308] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272287)
[ 2471.763701] Buffer I/O error on device mmcblk0p2, logical block 264462
[ 2471.770643] blk_update_request: I/O error, dev mmcblk0, sector 2178296
[ 2471.777542] EXT4-fs warning (device mmcblk0p2): ext4_end_bio:330: I/O error -5 writing to inode 13757 (offset 0 size 0 starting block 272288)
[ 2471.790930] Buffer I/O error on device mmcblk0p2, logical block 264463

    

Answer 1

O problema estava relacionado ao sistema que consome muita memória para registro no diário. Depois de reduzir a quantidade de memória alocada para o tmpfs e o diário do systemd, o problema desapareceu.