我们运行rsnapshot（rsync）并使用ionice和nice。 在备份内存使用结束时爆炸，下面的iSCSI错误开始出现。 这是运行Fedora 25的Dell PowerEdge 1850，具有4.9内核，8GB RAM，8GB交换。 这连接到称为VessRAID 1840i的硬件RAID。 我已经看到了禁用TCP窗口缩放的build议 。
另一个看似相关的线程有以下build议：
sysctl -w net.ipv4.tcp_tw_recycle=0 以及禁用TCP时间戳：
sysctl -w net.ipv4.tcp_timestamps=0 To make this change permanent, make an entry in /etc/sysctl.conf.
类似的声音错误，“ iscsid: Kernel reported iSCSI connection 1:0 error (1011) state (3)" ，我发现一个build议 ：
turn off iSCSI pings by setting: node.conn[0].timeo.noop_out_interval = 0 node.conn[0].timeo.noop_out_timeout = 0 And you can turn the replacement_timer to a very long value: node.session.timeo.replacement_timeout = 86400
当内存使用开始失控时，以下是来自/ var / log / messages的日志：
iscsid: Kernel reported iSCSI connection 1:0 error (1022 - Invalid or unknown error code) state (3) iscsid: connection1:0 is operational after recovery (1 attempts) chronyd[761]: Selected source 199.102.46.75 systemd: Starting dnf makecache... dnf: Metadata cache refreshed recently.'systemd: Started dnf makecache. systemd-logind: New session 10 of user root. systemd: Started Session 10 of user root. systemd-logind: Removed session 10. kernel: connection1:0: ping timeout of 5 secs expired, recv timeout 5, last rx 76580624, last ping 76585814, now 76591204 kernel: connection1:0: detected conn error (1022) iscsid: Kernel reported iSCSI connection 1:0 error (1022 - Invalid or unknown error code) state (3) iscsid: connection1:0 is operational after recovery (1 attempts) systemd: Starting dnf makecache... kernel: connection1:0: ping timeout of 5 secs expired, recv timeout 5, last rx 81687108, last ping 81692267, now 81700110
以及一些显示内存使用情况和内核日志的日志：
automount: page allocation stalls for 25608ms, order:1, mode:0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK) CPU: 3 PID: 1163 Comm: automount Not tainted 4.9.5-200.fc25.i686+PAE #1 Hardware name: Dell Computer Corporation PowerEdge 1850/0D8266, BIOS A07 04/25/2008 ee55fdb8 d6f6c6c0 d7578510 00000000 ee55fde8 d6d854a6 d757cc59 027000c0 ee55fdf0 ee55fdf8 d7578510 ee55fdcc 1cbb0e3b 00000001 d76fa158 00000001 ee55feb0 d6d86040 027000c0 d7578510 00006408 00000001 ee5a6480 00000013 Call Trace: [<d6f6c6c0>] dump_stack+0x58/0x78 [<d6d854a6>] warn_alloc+0xf6/0x110 [<d6d86040>] __alloc_pages_nodemask+0xb10/0xce0 [<d6dd5437>] ? kmem_cache_alloc+0xf7/0x1c0 [<d6c6aa89>] ? copy_process.part.44+0x549/0x14e0 [<d6c6a648>] copy_process.part.44+0x108/0x14e0 [<d6c94bf6>] ? check_preempt_curr+0x76/0x80 [<d6c6bbe4>] _do_fork+0xd4/0x370 [<d6c6bf6c>] SyS_clone+0x2c/0x30 [<d6c0369c>] do_int80_syscall_32+0x5c/0xc0 [<d73737e9>] entry_INT80_32+0x31/0x31 Mem-Info: active_anon:10713 inactive_anon:8264 isolated_anon:0#012 active_file:249801 inactive_file:1557433 isolated_file:0#012 unevictable:1968 dirty:2 writeback:0 unstable:0#012 slab_reclaimable:188422 slab_unreclaimable:5832#012 mapped:8048 shmem:245 pagetables:1236 bounce:0#012 free:42226 free_pcp:0 free_cma:0 Node 0 active_anon:42852kB inactive_anon:33056kB active_file:999204kB inactive_file:6229732kB unevictable:7872kB isolated(anon):0kB isolated(file):0kB mapped:32192kB dirty:8kB writeback:0kB shmem:980kB writeback_tmp:0kB unstable:0kB pages_scanned:0 all_unreclaimable? no DMA free:3040kB min:68kB low:84kB high:100kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15996kB managed:15916kB mlocked:0kB slab_reclaimable:12720kB slab_unreclaimable:92kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB lowmem_reserve[]: 0 751 8055 8055 Normal free:5440kB min:3472kB low:4340kB high:5208kB active_anon:0kB inactive_anon:0kB active_file:4276kB inactive_file:4088kB unevictable:0kB writepending:0kB present:892920kB managed:791232kB mlocked:0kB slab_reclaimable:740968kB slab_unreclaimable:23236kB kernel_stack:1408kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB lowmem_reserve[]: 0 0 58430 58430 HighMem free:160424kB min:512kB low:8944kB high:17376kB active_anon:42852kB inactive_anon:33056kB active_file:994928kB inactive_file:6225644kB unevictable:7872kB writepending:8kB present:7479040kB managed:7479040kB mlocked:7872kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:4944kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB lowmem_reserve[]: 0 0 0 0 DMA: 14*4kB (UME) 9*8kB (UME) 4*16kB (UM) 5*32kB (UME) 8*64kB (UME) 7*128kB (UME) 3*256kB (UE) 1*512kB (M) 0*1024kB 0*2048kB 0*4096kB = 3040kB Normal: 1032*4kB (UMEH) 126*8kB (UME) 20*16kB (UME) 6*32kB (UME) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 5648kB HighMem: 1476*4kB (UM) 3131*8kB (UM) 1817*16kB (UM) 730*32kB (UM) 497*64kB (UM) 161*128kB (M) 22*256kB (M) 38*512kB (M) 0*1024kB 0*2048kB 0*4096kB = 160888kB Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB 1809281 total pagecache pages 228 pages in swap cache Swap cache stats: add 5032, delete 4804, find 7386/7796 Free swap = 8342136kB Total swap = 8355836kB 2096989 pages RAM 1869760 pages HighMem/MovableOnly 25442 pages reserved 0 pages hwpoisoned
我上面提到的那些讨论有关吗？ 我应该尝试哪些设置更改？
也看到像这样的错误：
kernel: perf: interrupt took too long (9721 > 9697), lowering kernel.perf_event_max_sample_rate to 20000 kernel: [<d7374857>] error_code+0x67/0x6c
我收到了一位Linux内核维护人员的回复。 这似乎是32位内核和低内存压力的问题 。 这里有一些意见（我提供了更多的日志和跟踪点）：
所有这些都是从kswapd （背景记忆回收）。 这意味着它没有捕获任何可能拖延太久的分配。 无论如何，上面的tracepoint表明我们能够在回收期间取得一些进展（nr_reclaimed> 0）。 所以我怀疑这确实是一个很大的低压，我不明白我们能做些什么。
以及：
而这一个正在打最小的水印，而没有真正的回收。 只有页面caching可能被固定，不能从这个上下文中回收，因为这是GFP_NOFS请求。 为了获得一些回忆而回收的情景并不令人惊讶。 有大量的可回收板可能只是缓慢的进展。
这恐怕不是32b系统上令人惊讶的事情。
看来这不是很快就会得到修复的东西，如果有的话。 FWIW我在/etc/sysctl.conf有这些设置
# Disable TCP window scaling net.ipv4.tcp_window_scaling=0 # tip from http://serverfault.com/questions/235965/why-would-a-server-not-send-a-syn-ack-packet-in-response-to-a-syn-packet net.ipv4.tcp_timestamps=0 net.ipv4.tcp_tw_recycle=0 # vm.zone_reclaim_mode=1 CONFIG_NUMA needs to be enabled in kernel configuration for this setting vm.min_free_kbytes=131072 #tip from https://www.spinics.net/lists/kernel/msg2403670.html # write-cache, foreground/background flushing vm.dirty_ratio = 3 # vm.dirty_background_ratio = 5 (% of RAM) vm.dirty_background_ratio = 1 # make it 10 sec vm.dirty_writeback_centisecs = 1000 # http://serverfault.com/questions/696156/kswapd-often-uses-100-cpu-when-swap-is-in-use vm.swappiness=25 vm.vfs_cache_pressure=1000