Hi everyone, Recently when I upgrade my kernel from 3.12.61 to kernel 4.4.74, I find my system sometimes is very slow and unresponsive When my system is under a heavy IO load, I see the node start to respond very slow, the IO wait time keeps very high, and the node starts unresponsive. I try to dump all block task at that time and found some interesting things, look like under a heavy load I/O, the kswap start to hang in jbd2_log_wait_commit. Sep 07 12:25:35 myPC kernel: [11039.126514] kswapd0 D 0000000000000000 0 26 2 0x00000000 Sep 07 12:25:35 myPC kernel: [11039.126517] ffff88003da27b78 ffff88000ce08280 ffff88003cdf0680 ffff88003da28000 Sep 07 12:25:35 myPC kernel: [11039.126519] ffff88001a15c888 ffff88001a15c824 ffff88003da27bb8 ffff88001a15c8a0 Sep 07 12:25:35 myPC kernel: [11039.126521] ffff88003da27b90 ffffffff815e4c85 ffff88001a15c800 0000000000013183 Sep 07 12:25:35 myPC kernel: [11039.126522] Call Trace: Sep 07 12:25:35 myPC kernel: [11039.126539] [<ffffffff815e4c85>] schedule+0x35/0x80 Sep 07 12:25:35 myPC kernel: [11039.126561] [<ffffffffa02faada>] jbd2_log_wait_commit+0x8a/0xf0 [jbd2] Sep 07 12:25:35 myPC kernel: [11039.126621] [<ffffffffa03b28a4>] ext4_evict_inode+0x2d4/0x4b0 [ext4] Sep 07 12:25:35 myPC kernel: [11039.126630] [<ffffffff81215a7a>] evict+0xba/0x190 Sep 07 12:25:35 myPC kernel: [11039.126635] [<ffffffff81215b82>] dispose_list+0x32/0x50 Sep 07 12:25:35 myPC kernel: [11039.126639] [<ffffffff81216e52>] prune_icache_sb+0x42/0x50 Sep 07 12:25:35 myPC kernel: [11039.126644] [<ffffffff811ff8f6>] super_cache_scan+0x136/0x180 Sep 07 12:25:35 myPC kernel: [11039.126653] [<ffffffff81196a1b>] shrink_slab.part.41+0x20b/0x3f0 Sep 07 12:25:35 myPC kernel: [11039.126521] ffff88003da27b90 ffffffff815e4c85 ffff88001a15c800 0000000000013183 And after that more and more processes are hitting STAT D, nfsd is hang to wait or the inode deletion to complete in __wait_on_freeing_inode. Sep 07 12:25:35 myPC kernel: [11039.390218] nfsd D 0000000000000000 0 30419 2 0x00000080 Sep 07 12:25:35 myPC kernel: [11039.390221] ffff88000da47a98 ffff8800277ec380 ffff8800374ec580 ffff88000da48000 Sep 07 12:25:35 myPC kernel: [11039.390223] ffff88000da47ad8 ffffc9000011edc8 0000000000000000 ffff88000e92e2f8 Sep 07 12:25:35 myPC kernel: [11039.390225] ffff88000da47ab0 ffffffff815e4c85 ffffffff81c094c0 ffff88003ff9d8b8 Sep 07 12:25:35 myPC kernel: [11039.390225] Call Trace: Sep 07 12:25:35 myPC kernel: [11039.390231] [<ffffffff815e4c85>] schedule+0x35/0x80 Sep 07 12:25:35 myPC kernel: [11039.390236] [<ffffffff812157fc>] __wait_on_freeing_inode+0x9c/0xc0 Sep 07 12:25:35 myPC kernel: [11039.390241] [<ffffffff81215d83>] find_inode_fast+0x73/0xa0 Sep 07 12:25:35 myPC kernel: [11039.390245] [<ffffffff81216052>] iget_locked+0x72/0x190 Sep 07 12:25:35 myPC kernel: [11039.390284] [<ffffffffa03aeb8c>] ext4_iget+0x2c/0xb10 [ext4] Sep 07 12:25:35 myPC kernel: [11039.390314] [<ffffffffa03c1055>] ext4_nfs_get_inode+0x45/0x80 [ext4] Sep 07 12:25:35 myPC kernel: [11039.390320] [<ffffffff812211c4>] generic_fh_to_dentry+0x24/0x30 Sep 07 12:25:35 myPC kernel: [11039.390326] [<ffffffff81277ede>] exportfs_decode_fh+0x5e/0x350 Sep 07 12:25:35 myPC kernel: [11039.390347] [<ffffffffa047749a>] fh_verify+0x2da/0x5a0 [nfsd] Sep 07 12:25:35 myPC kernel: [11039.390362] [<ffffffffa0480933>] nfsd3_proc_getattr+0x63/0xd0 [nfsd] Sep 07 12:25:35 myPC kernel: [11039.390374] [<ffffffffa0473e23>] nfsd_dispatch+0xc3/0x260 [nfsd] Sep 07 12:25:35 myPC kernel: [11039.390411] [<ffffffffa0322108>] svc_process_common+0x418/0x6a0 [sunrpc] Sep 07 12:25:35 myPC kernel: [11039.390439] [<ffffffffa032248d>] svc_process+0xfd/0x1b0 [sunrpc] Sep 07 12:25:35 myPC kernel: [11039.390454] [<ffffffffa047389a>] nfsd+0xea/0x160 [nfsd] That causes the other nfs client is hang to wait nfsd to continue. Sep 07 12:25:35 myPC kernel: [11039.207987] Call Trace: Sep 07 12:25:35 myPC kernel: [11039.207994] [<ffffffff815e4c85>] schedule+0x35/0x80 Sep 07 12:25:35 myPC kernel: [11039.208008] [<ffffffffa031acce>] rpc_wait_bit_killable+0x1e/0xa0 [sunrpc] Sep 07 12:25:35 myPC kernel: [11039.208055] [<ffffffff815e5098>] __wait_on_bit+0x58/0x90 Sep 07 12:25:35 myPC kernel: [11039.208059] [<ffffffff815e513e>] out_of_line_wait_on_bit+0x6e/0x80 Sep 07 12:25:35 myPC kernel: [11039.208082] [<ffffffffa031bd26>] __rpc_execute+0x146/0x440 [sunrpc] Sep 07 12:25:35 myPC kernel: [11039.208104] [<ffffffffa0313049>] rpc_run_task+0x69/0x80 [sunrpc] Sep 07 12:25:35 myPC kernel: [11039.208126] [<ffffffffa031309f>] rpc_call_sync+0x3f/0xa0 [sunrpc] Sep 07 12:25:35 myPC kernel: [11039.204818] [<ffffffff81200d69>] vfs_fstatat+0x49/0x90 Sep 07 12:25:35 myPC kernel: [11039.204821] [<ffffffff812011ea>] SYSC_newstat+0x1a/0x40 Sep 07 12:25:35 myPC kernel: [11039.204826] [<ffffffff815e876e>] entry_SYSCALL_64_fastpath+0x12/0x6d Sep 07 12:25:35 myPC kernel: [11039.207972] DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x6d I guess under heavy load, somehow the inode cannot be evicted in kswap, so the nfsd just keeps waiting and cause the whole system ends up in unresponsive state. I found some related issues https://www.systutorials.com/linux-kernels/105429/nfsv4-1-prevent-a-3-way-de... (it’s not the same as it’s nfsv4 but just refer for the same symptom.) My system has very limited resource, only 1 core and 1GB RAM and the issue is very easy to happen in a slow disk. However, I did not see the same issue in the older kernel 3.12.61. Could you please let me know if my analysis makes sense, if jbd2_log_wait_commit hang causes __wait_on_freeing_inode wait ? Is it a known issue in kernel? If any kernel change causes the issue?. And if we have any WA to avoid that like preventing kswapd kicks in (I have a 5G swap partition) or to make my system is not unresponsive like that (of course it is not to add more RAM :) ? Thanks a lot Brs, Naruto