RHEL7: I/O stalled from critical I/O task being throttled by throttle_vm_writeout

Issue

• Hang occurred with following log:

[966792.129150] INFO: task kswapd1:308 blocked for more than 120 seconds.
[966792.129208] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[966792.129270] kswapd1         D ffff88613fb66eb0     0   308      2 0x00000080
[966792.129278] Call Trace:
[966792.129288]  [<ffffffff97312f49>] schedule+0x29/0x70
[966792.129313]  [<ffffffffc084778e>] raid1_write_request+0x7ae/0xa10 [raid1]
[966792.129321]  [<ffffffff96df835b>] ? __kmalloc+0x1eb/0x230
[966792.129329]  [<ffffffffc0846fd4>] ? r1bio_pool_alloc+0x24/0x30 [raid1]
[966792.129341]  [<ffffffff96d96afe>] ? mempool_alloc+0x6e/0x170
[966792.129346]  [<ffffffff96cbbe20>] ? wake_up_atomic_t+0x30/0x30
[966792.129355]  [<ffffffffc0847a82>] raid1_make_request+0x92/0x500 [raid1]
[966792.129361]  [<ffffffff96d969a5>] ? mempool_alloc_slab+0x15/0x20
[966792.129372]  [<ffffffff97147ba0>] md_handle_request+0xd0/0x150
[966792.129396]  [<ffffffffc049eba8>] raid_map+0x28/0x40 [dm_raid]
[966792.129419]  [<ffffffffc03f1126>] __map_bio+0x96/0x190 [dm_mod]
[966792.129432]  [<ffffffffc03ef680>] ? queue_io+0x80/0x80 [dm_mod]
[966792.129447]  [<ffffffffc03f1427>] __clone_and_map_data_bio+0x177/0x280 [dm_mod]
[966792.129461]  [<ffffffffc03f1801>] __split_and_process_bio+0x2d1/0x520 [dm_mod]
[966792.129475]  [<ffffffffc03f1d6d>] dm_make_request+0x11d/0x1a0 [dm_mod]
[966792.129500]  [<ffffffff96f1a6bb>] generic_make_request+0x10b/0x320
[966792.129504]  [<ffffffff96e57395>] ? bio_alloc_bioset+0x115/0x310
[966792.129506]  [<ffffffff96f1a940>] submit_bio+0x70/0x150
[966792.129511]  [<ffffffff96dd9860>] ? init_emergency_isa_pool+0x60/0x60
[966792.129513]  [<ffffffff96dd9e09>] __swap_writepage+0x239/0x280
[966792.129517]  [<ffffffff96dd229e>] ? page_remove_rmap+0xce/0x160
[966792.129520]  [<ffffffff96dd25bf>] ? try_to_unmap_one+0x28f/0x7c0
[966792.129522]  [<ffffffff96ddab32>] ? _swap_info_get+0x12/0x60
[966792.129525]  [<ffffffff96ddc8b0>] ? page_swapcount+0x50/0xa0
[966792.129527]  [<ffffffff96dd9e89>] swap_writepage+0x39/0x80
[966792.129531]  [<ffffffff96da814f>] shrink_page_list+0x4df/0xaf0
[966792.129534]  [<ffffffff96da8d8d>] shrink_inactive_list+0x1cd/0x5d0
[966792.129536]  [<ffffffff96da9885>] shrink_lruvec+0x385/0x730
[966792.129539]  [<ffffffff96da9ca6>] shrink_zone+0x76/0x1a0
[966792.129541]  [<ffffffff96daaf9c>] balance_pgdat+0x48c/0x5e0
[966792.129544]  [<ffffffff96dab263>] kswapd+0x173/0x440
[966792.129545]  [<ffffffff96cbbe20>] ? wake_up_atomic_t+0x30/0x30
[966792.129547]  [<ffffffff96dab0f0>] ? balance_pgdat+0x5e0/0x5e0
[966792.129551]  [<ffffffff96cbae31>] kthread+0xd1/0xe0
[966792.129553]  [<ffffffff96cbad60>] ? insert_kthread_work+0x40/0x40
[966792.129556]  [<ffffffff9731f637>] ret_from_fork_nospec_begin+0x21/0x21
[966792.129558]  [<ffffffff96cbad60>] ? insert_kthread_work+0x40/0x40