Spoke too soon, though it may be a slightly different issue, but still appears to be BTRFS related. This is still on 4.6.0-040600rc6-generic, the memory on this server is 1GB.

[121025.879323] SLUB: Unable to allocate memory on node -1, gfp=0x2080020(GFP_ATOMIC)
[121025.879324]   cache: kmalloc-256, object size: 256, buffer size: 256, default order: 0, min order: 0
[121025.879324]   node 0: slabs: 148, objs: 2368, free: 0
[121025.879517] kworker/u4:2: page allocation failure: order:0, mode:0x2200020(GFP_NOWAIT|__GFP_HIGH|__GFP_NOTRACK)
[121025.879519] CPU: 1 PID: 9038 Comm: kworker/u4:2 Not tainted 4.6.0-040600rc6-generic #201605012031
[121025.879520] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[121025.879572] Workqueue: btrfs-worker btrfs_worker_helper [btrfs]
[121025.879574]  0000000000000086 00000000d14aff48 ffff88003fd03960 ffffffff813ef3b3
[121025.879576]  0000000000000000 0000000000000000 ffff88003fd039f0 ffffffff8119b3d4
[121025.879577]  0220002079d790e3 ffff88003fffb6e0 ffffffff82110ae0 ffffffff00000060
[121025.879579] Call Trace:
[121025.879580]  <IRQ>  [<ffffffff813ef3b3>] dump_stack+0x63/0x90
[121025.879584]  [<ffffffff8119b3d4>] warn_alloc_failed+0x104/0x160
[121025.879586]  [<ffffffff8119f059>] __alloc_pages_nodemask+0x4f9/0xc30
[121025.879588]  [<ffffffff810dc3f1>] ? vprintk_emit+0x2a1/0x4d0
[121025.879590]  [<ffffffff811ef0bc>] alloc_pages_current+0x8c/0x110
[121025.879592]  [<ffffffff811f9252>] new_slab+0x452/0x5c0
[121025.879593]  [<ffffffff811fa2c9>] ___slab_alloc+0x249/0x480
[121025.879595]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.879596]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.879598]  [<ffffffff811fa520>] __slab_alloc+0x20/0x40
[121025.879599]  [<ffffffff811fa6d2>] kmem_cache_alloc+0x192/0x1d0
[121025.879600]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.879601]  [<ffffffff81723aea>] __build_skb+0x2a/0xe0
[121025.879603]  [<ffffffff81723dc8>] __napi_alloc_skb+0x98/0xd0
[121025.879605]  [<ffffffff81603da6>] page_to_skb.isra.28+0x66/0x310
[121025.879607]  [<ffffffff8160617f>] virtnet_receive+0x2df/0xa00
[121025.879609]  [<ffffffff810a8b28>] ? update_rq_clock.part.81+0x18/0x40
[121025.879610]  [<ffffffff816068bd>] virtnet_poll+0x1d/0x80
[121025.879612]  [<ffffffff81733705>] net_rx_action+0x225/0x360
[121025.879615]  [<ffffffff818433a6>] __do_softirq+0xf6/0x27e
[121025.879616]  [<ffffffff81088483>] irq_exit+0xa3/0xb0
[121025.879617]  [<ffffffff81843104>] do_IRQ+0x54/0xd0
[121025.879619]  [<ffffffff81841202>] common_interrupt+0x82/0x82
[121025.879619]  <EOI>  [<ffffffff811ad389>] ? shrink_inactive_list+0x199/0x500
[121025.879623]  [<ffffffff811ad5f5>] ? shrink_inactive_list+0x405/0x500
[121025.879626]  [<ffffffff811ae09d>] shrink_zone_memcg+0x5ad/0x7a0
[121025.879627]  [<ffffffff811a9500>] ? shrink_slab.part.39+0x240/0x3e0
[121025.879634]  [<ffffffff8111975c>] ? css_next_descendant_pre+0x4c/0x60
[121025.879636]  [<ffffffff8111975c>] ? css_next_descendant_pre+0x4c/0x60
[121025.879638]  [<ffffffff811ae370>] shrink_zone+0xe0/0x300
[121025.879640]  [<ffffffff811ae70e>] do_try_to_free_pages+0x17e/0x430
[121025.879642]  [<ffffffff811aea8e>] try_to_free_pages+0xce/0x180
[121025.879644]  [<ffffffff8119f124>] __alloc_pages_nodemask+0x5c4/0xc30
[121025.879646]  [<ffffffff810b7e09>] ? set_next_entity+0x49/0xd0
[121025.879647]  [<ffffffff811ef0bc>] alloc_pages_current+0x8c/0x110
[121025.879649]  [<ffffffff811f9252>] new_slab+0x452/0x5c0
[121025.879651]  [<ffffffff811fa2c9>] ___slab_alloc+0x249/0x480
[121025.879661]  [<ffffffffc016482a>] ? btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.879668]  [<ffffffff813afdd7>] ? chksum_update+0x17/0x20
[121025.879669]  [<ffffffff813a6910>] ? crypto_shash_update+0x30/0xe0
[121025.879679]  [<ffffffffc016482a>] ? btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.879681]  [<ffffffff811fa520>] __slab_alloc+0x20/0x40
[121025.879682]  [<ffffffff811fbea4>] __kmalloc+0x1c4/0x230
[121025.879691]  [<ffffffffc0167500>] ? run_one_async_free+0x20/0x20 [btrfs]
[121025.879700]  [<ffffffffc016482a>] btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.879709]  [<ffffffffc0167500>] ? run_one_async_free+0x20/0x20 [btrfs]
[121025.879718]  [<ffffffffc017426d>] __btrfs_submit_bio_start+0x1d/0x30 [btrfs]
[121025.879727]  [<ffffffffc01672a6>] run_one_async_start+0x26/0x30 [btrfs]
[121025.879738]  [<ffffffffc01a489a>] btrfs_scrubparity_helper+0xca/0x2e0 [btrfs]
[121025.879749]  [<ffffffffc01a4bfe>] btrfs_worker_helper+0xe/0x10 [btrfs]
[121025.879753]  [<ffffffff8109cad8>] process_one_work+0x168/0x480
[121025.879755]  [<ffffffff8109ce3b>] worker_thread+0x4b/0x500
[121025.879757]  [<ffffffff8109cdf0>] ? process_one_work+0x480/0x480
[121025.879758]  [<ffffffff810a3228>] kthread+0xd8/0xf0
[121025.879760]  [<ffffffff81840ae2>] ret_from_fork+0x22/0x40
[121025.879763]  [<ffffffff810a3150>] ? kthread_create_on_node+0x1a0/0x1a0
[121025.879764] Mem-Info:
[121025.879766] active_anon:18131 inactive_anon:23781 isolated_anon:0
                 active_file:84105 inactive_file:84587 isolated_file:19
                 unevictable:1762 dirty:869 writeback:23497 unstable:0
                 slab_reclaimable:25801 slab_unreclaimable:5224
                 mapped:33650 shmem:34217 pagetables:1605 bounce:0
                 free:1897 free_pcp:20 free_cma:0
[121025.879769] Node 0 DMA free:3920kB min:60kB low:72kB high:84kB active_anon:188kB inactive_anon:1324kB active_file:2540kB inactive_file:2664kB unevictable:112kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlocked:112kB dirty:0kB writeback:80kB mapped:884kB shmem:1356kB slab_reclaimable:2296kB slab_unreclaimable:284kB kernel_stack:64kB pagetables:80kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[121025.879772] lowmem_reserve[]: 0 973 973 973 973
[121025.879775] Node 0 DMA32 free:3668kB min:3824kB low:4820kB high:5816kB active_anon:72336kB inactive_anon:93800kB active_file:333880kB inactive_file:335684kB unevictable:6936kB isolated(anon):0kB isolated(file):76kB present:1032184kB managed:1000480kB mlocked:6936kB dirty:3476kB writeback:93908kB mapped:133716kB shmem:135512kB slab_reclaimable:100908kB slab_unreclaimable:20612kB kernel_stack:3296kB pagetables:6340kB unstable:0kB bounce:0kB free_pcp:80kB local_pcp:80kB free_cma:0kB writeback_tmp:0kB pages_scanned:160 all_unreclaimable? no
[121025.879779] lowmem_reserve[]: 0 0 0 0 0
[121025.879781] Node 0 DMA: 361*4kB (UME) 59*8kB (UEH) 1*16kB (H) 0*32kB 1*64kB (H) 1*128kB (H) 1*256kB (H) 1*512kB (H) 1*1024kB (H) 0*2048kB 0*4096kB = 3916kB
[121025.879788] Node 0 DMA32: 836*4kB (UMH) 22*8kB (UH) 16*16kB (H) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 3776kB
[121025.879794] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[121025.879795] 204488 total pagecache pages
[121025.879796] 675 pages in swap cache
[121025.879796] Swap cache stats: add 42167, delete 41492, find 1069663/1070758
[121025.879797] Free swap  = 897344kB
[121025.879798] Total swap = 1046524kB
[121025.879799] 262044 pages RAM
[121025.879800] 0 pages HighMem/MovableOnly
[121025.879800] 7947 pages reserved
[121025.879801] 0 pages cma reserved
[121025.879801] 0 pages hwpoisoned
[121025.879803] SLUB: Unable to allocate memory on node -1, gfp=0x2080020(GFP_ATOMIC)
[121025.879804]   cache: kmalloc-256, object size: 256, buffer size: 256, default order: 0, min order: 0
[121025.879804]   node 0: slabs: 148, objs: 2368, free: 0
[121025.879807] kworker/u4:2: page allocation failure: order:0, mode:0x2200020(GFP_NOWAIT|__GFP_HIGH|__GFP_NOTRACK)
[121025.879808] CPU: 1 PID: 9038 Comm: kworker/u4:2 Not tainted 4.6.0-040600rc6-generic #201605012031
[121025.879809] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[121025.879819] Workqueue: btrfs-worker btrfs_worker_helper [btrfs]
[121025.879820]  0000000000000086 00000000d14aff48 ffff88003fd03960 ffffffff813ef3b3
[121025.879822]  0000000000000000 0000000000000000 ffff88003fd039f0 ffffffff8119b3d4
[121025.879823]  02200020d14aff48 ffff88003fffb6e0 ffffffff82110ae0 ffffffff00000060
[121025.879824] Call Trace:
[121025.879825]  <IRQ>  [<ffffffff813ef3b3>] dump_stack+0x63/0x90
[121025.879829]  [<ffffffff8119b3d4>] warn_alloc_failed+0x104/0x160
[121025.879831]  [<ffffffff8119f059>] __alloc_pages_nodemask+0x4f9/0xc30
[121025.879833]  [<ffffffff810dc3f1>] ? vprintk_emit+0x2a1/0x4d0
[121025.879834]  [<ffffffff811ef0bc>] alloc_pages_current+0x8c/0x110
[121025.879836]  [<ffffffff811f9252>] new_slab+0x452/0x5c0
[121025.879837]  [<ffffffff811fa2c9>] ___slab_alloc+0x249/0x480
[121025.879839]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.879841]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.879842]  [<ffffffff811fa520>] __slab_alloc+0x20/0x40
[121025.879843]  [<ffffffff811fa6d2>] kmem_cache_alloc+0x192/0x1d0
[121025.879844]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.879846]  [<ffffffff81723aea>] __build_skb+0x2a/0xe0
[121025.879849]  [<ffffffff81723dc8>] __napi_alloc_skb+0x98/0xd0
[121025.879857]  [<ffffffff81603da6>] page_to_skb.isra.28+0x66/0x310
[121025.879859]  [<ffffffff8160617f>] virtnet_receive+0x2df/0xa00
[121025.879861]  [<ffffffff810a8b28>] ? update_rq_clock.part.81+0x18/0x40
[121025.879863]  [<ffffffff816068bd>] virtnet_poll+0x1d/0x80
[121025.879864]  [<ffffffff81733705>] net_rx_action+0x225/0x360
[121025.879866]  [<ffffffff818433a6>] __do_softirq+0xf6/0x27e
[121025.879867]  [<ffffffff81088483>] irq_exit+0xa3/0xb0
[121025.879869]  [<ffffffff81843104>] do_IRQ+0x54/0xd0
[121025.879871]  [<ffffffff81841202>] common_interrupt+0x82/0x82
[121025.879871]  <EOI>  [<ffffffff811ad389>] ? shrink_inactive_list+0x199/0x500
[121025.879875]  [<ffffffff811ad5f5>] ? shrink_inactive_list+0x405/0x500
[121025.879877]  [<ffffffff811ae09d>] shrink_zone_memcg+0x5ad/0x7a0
[121025.879879]  [<ffffffff811a9500>] ? shrink_slab.part.39+0x240/0x3e0
[121025.879881]  [<ffffffff8111975c>] ? css_next_descendant_pre+0x4c/0x60
[121025.879882]  [<ffffffff8111975c>] ? css_next_descendant_pre+0x4c/0x60
[121025.879885]  [<ffffffff811ae370>] shrink_zone+0xe0/0x300
[121025.879886]  [<ffffffff811ae70e>] do_try_to_free_pages+0x17e/0x430
[121025.879888]  [<ffffffff811aea8e>] try_to_free_pages+0xce/0x180
[121025.879890]  [<ffffffff8119f124>] __alloc_pages_nodemask+0x5c4/0xc30
[121025.879892]  [<ffffffff810b7e09>] ? set_next_entity+0x49/0xd0
[121025.879894]  [<ffffffff811ef0bc>] alloc_pages_current+0x8c/0x110
[121025.879895]  [<ffffffff811f9252>] new_slab+0x452/0x5c0
[121025.879896]  [<ffffffff811fa2c9>] ___slab_alloc+0x249/0x480
[121025.879905]  [<ffffffffc016482a>] ? btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.879908]  [<ffffffff813afdd7>] ? chksum_update+0x17/0x20
[121025.879909]  [<ffffffff813a6910>] ? crypto_shash_update+0x30/0xe0
[121025.879917]  [<ffffffffc016482a>] ? btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.879919]  [<ffffffff811fa520>] __slab_alloc+0x20/0x40
[121025.879921]  [<ffffffff811fbea4>] __kmalloc+0x1c4/0x230
[121025.879929]  [<ffffffffc0167500>] ? run_one_async_free+0x20/0x20 [btrfs]
[121025.879938]  [<ffffffffc016482a>] btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.879947]  [<ffffffffc0167500>] ? run_one_async_free+0x20/0x20 [btrfs]
[121025.879956]  [<ffffffffc017426d>] __btrfs_submit_bio_start+0x1d/0x30 [btrfs]
[121025.879965]  [<ffffffffc01672a6>] run_one_async_start+0x26/0x30 [btrfs]
[121025.879975]  [<ffffffffc01a489a>] btrfs_scrubparity_helper+0xca/0x2e0 [btrfs]
[121025.879985]  [<ffffffffc01a4bfe>] btrfs_worker_helper+0xe/0x10 [btrfs]
[121025.879988]  [<ffffffff8109cad8>] process_one_work+0x168/0x480
[121025.879990]  [<ffffffff8109ce3b>] worker_thread+0x4b/0x500
[121025.879992]  [<ffffffff8109cdf0>] ? process_one_work+0x480/0x480
[121025.879993]  [<ffffffff810a3228>] kthread+0xd8/0xf0
[121025.879995]  [<ffffffff81840ae2>] ret_from_fork+0x22/0x40
[121025.879996]  [<ffffffff810a3150>] ? kthread_create_on_node+0x1a0/0x1a0
[121025.879998] Mem-Info:
[121025.880000] active_anon:18131 inactive_anon:23781 isolated_anon:0
                 active_file:84105 inactive_file:84587 isolated_file:19
                 unevictable:1762 dirty:869 writeback:23497 unstable:0
                 slab_reclaimable:25801 slab_unreclaimable:5224
                 mapped:33650 shmem:34217 pagetables:1605 bounce:0
                 free:1897 free_pcp:20 free_cma:0
[121025.880002] Node 0 DMA free:3920kB min:60kB low:72kB high:84kB active_anon:188kB inactive_anon:1324kB active_file:2540kB inactive_file:2664kB unevictable:112kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlocked:112kB dirty:0kB writeback:80kB mapped:884kB shmem:1356kB slab_reclaimable:2296kB slab_unreclaimable:284kB kernel_stack:64kB pagetables:80kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[121025.880006] lowmem_reserve[]: 0 973 973 973 973
[121025.880008] Node 0 DMA32 free:3668kB min:3824kB low:4820kB high:5816kB active_anon:72336kB inactive_anon:93800kB active_file:333880kB inactive_file:335684kB unevictable:6936kB isolated(anon):0kB isolated(file):76kB present:1032184kB managed:1000480kB mlocked:6936kB dirty:3476kB writeback:93908kB mapped:133716kB shmem:135512kB slab_reclaimable:100908kB slab_unreclaimable:20612kB kernel_stack:3296kB pagetables:6340kB unstable:0kB bounce:0kB free_pcp:80kB local_pcp:80kB free_cma:0kB writeback_tmp:0kB pages_scanned:160 all_unreclaimable? no
[121025.880014] lowmem_reserve[]: 0 0 0 0 0
[121025.880016] Node 0 DMA: 361*4kB (UME) 59*8kB (UEH) 1*16kB (H) 0*32kB 1*64kB (H) 1*128kB (H) 1*256kB (H) 1*512kB (H) 1*1024kB (H) 0*2048kB 0*4096kB = 3916kB
[121025.880023] Node 0 DMA32: 836*4kB (UMH) 22*8kB (UH) 16*16kB (H) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 3776kB
[121025.880029] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[121025.880030] 204488 total pagecache pages
[121025.880030] 675 pages in swap cache
[121025.880031] Swap cache stats: add 42167, delete 41492, find 1069663/1070758
[121025.880032] Free swap  = 897344kB
[121025.880033] Total swap = 1046524kB
[121025.880034] 262044 pages RAM
[121025.880035] 0 pages HighMem/MovableOnly
[121025.880035] 7947 pages reserved
[121025.880036] 0 pages cma reserved
[121025.880036] 0 pages hwpoisoned
[121025.880038] SLUB: Unable to allocate memory on node -1, gfp=0x2080020(GFP_ATOMIC)
[121025.880039]   cache: kmalloc-256, object size: 256, buffer size: 256, default order: 0, min order: 0
[121025.880040]   node 0: slabs: 148, objs: 2368, free: 0
[121025.880042] kworker/u4:2: page allocation failure: order:0, mode:0x2200020(GFP_NOWAIT|__GFP_HIGH|__GFP_NOTRACK)
[121025.880044] CPU: 1 PID: 9038 Comm: kworker/u4:2 Not tainted 4.6.0-040600rc6-generic #201605012031
[121025.880044] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[121025.880054] Workqueue: btrfs-worker btrfs_worker_helper [btrfs]
[121025.880056]  0000000000000086 00000000d14aff48 ffff88003fd03960 ffffffff813ef3b3
[121025.880057]  0000000000000000 0000000000000000 ffff88003fd039f0 ffffffff8119b3d4
[121025.880059]  02200020d14aff48 ffff88003fffb6e0 ffffffff82110ae0 ffffffff00000060
[121025.880060] Call Trace:
[121025.880061]  <IRQ>  [<ffffffff813ef3b3>] dump_stack+0x63/0x90
[121025.880064]  [<ffffffff8119b3d4>] warn_alloc_failed+0x104/0x160
[121025.880066]  [<ffffffff8119f059>] __alloc_pages_nodemask+0x4f9/0xc30
[121025.880068]  [<ffffffff810dc3f1>] ? vprintk_emit+0x2a1/0x4d0
[121025.880070]  [<ffffffff811ef0bc>] alloc_pages_current+0x8c/0x110
[121025.880071]  [<ffffffff811f9252>] new_slab+0x452/0x5c0
[121025.880073]  [<ffffffff811fa2c9>] ___slab_alloc+0x249/0x480
[121025.880075]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.880076]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.880077]  [<ffffffff811fa520>] __slab_alloc+0x20/0x40
[121025.880079]  [<ffffffff811fa6d2>] kmem_cache_alloc+0x192/0x1d0
[121025.880080]  [<ffffffff81723aea>] ? __build_skb+0x2a/0xe0
[121025.880082]  [<ffffffff81723aea>] __build_skb+0x2a/0xe0
[121025.880083]  [<ffffffff81723dc8>] __napi_alloc_skb+0x98/0xd0
[121025.880085]  [<ffffffff81603da6>] page_to_skb.isra.28+0x66/0x310
[121025.880087]  [<ffffffff8160617f>] virtnet_receive+0x2df/0xa00
[121025.880088]  [<ffffffff810a8b28>] ? update_rq_clock.part.81+0x18/0x40
[121025.880091]  [<ffffffff816068bd>] virtnet_poll+0x1d/0x80
[121025.880092]  [<ffffffff81733705>] net_rx_action+0x225/0x360
[121025.880094]  [<ffffffff818433a6>] __do_softirq+0xf6/0x27e
[121025.880095]  [<ffffffff81088483>] irq_exit+0xa3/0xb0
[121025.880097]  [<ffffffff81843104>] do_IRQ+0x54/0xd0
[121025.880098]  [<ffffffff81841202>] common_interrupt+0x82/0x82
[121025.880099]  <EOI>  [<ffffffff811ad389>] ? shrink_inactive_list+0x199/0x500
[121025.880103]  [<ffffffff811ad5f5>] ? shrink_inactive_list+0x405/0x500
[121025.880105]  [<ffffffff811ae09d>] shrink_zone_memcg+0x5ad/0x7a0
[121025.880106]  [<ffffffff811a9500>] ? shrink_slab.part.39+0x240/0x3e0
[121025.880109]  [<ffffffff8111975c>] ? css_next_descendant_pre+0x4c/0x60
[121025.880110]  [<ffffffff8111975c>] ? css_next_descendant_pre+0x4c/0x60
[121025.880112]  [<ffffffff811ae370>] shrink_zone+0xe0/0x300
[121025.880116]  [<ffffffff811ae70e>] do_try_to_free_pages+0x17e/0x430
[121025.880119]  [<ffffffff811aea8e>] try_to_free_pages+0xce/0x180
[121025.880120]  [<ffffffff8119f124>] __alloc_pages_nodemask+0x5c4/0xc30
[121025.880122]  [<ffffffff810b7e09>] ? set_next_entity+0x49/0xd0
[121025.880123]  [<ffffffff811ef0bc>] alloc_pages_current+0x8c/0x110
[121025.880125]  [<ffffffff811f9252>] new_slab+0x452/0x5c0
[121025.880127]  [<ffffffff811fa2c9>] ___slab_alloc+0x249/0x480
[121025.880136]  [<ffffffffc016482a>] ? btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.880138]  [<ffffffff813afdd7>] ? chksum_update+0x17/0x20
[121025.880139]  [<ffffffff813a6910>] ? crypto_shash_update+0x30/0xe0
[121025.880148]  [<ffffffffc016482a>] ? btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.880149]  [<ffffffff811fa520>] __slab_alloc+0x20/0x40
[121025.880151]  [<ffffffff811fbea4>] __kmalloc+0x1c4/0x230
[121025.880159]  [<ffffffffc0167500>] ? run_one_async_free+0x20/0x20 [btrfs]
[121025.880168]  [<ffffffffc016482a>] btrfs_csum_one_bio+0x6a/0x430 [btrfs]
[121025.880177]  [<ffffffffc0167500>] ? run_one_async_free+0x20/0x20 [btrfs]
[121025.880186]  [<ffffffffc017426d>] __btrfs_submit_bio_start+0x1d/0x30 [btrfs]
[121025.880195]  [<ffffffffc01672a6>] run_one_async_start+0x26/0x30 [btrfs]
[121025.880205]  [<ffffffffc01a489a>] btrfs_scrubparity_helper+0xca/0x2e0 [btrfs]
[121025.880215]  [<ffffffffc01a4bfe>] btrfs_worker_helper+0xe/0x10 [btrfs]
[121025.880217]  [<ffffffff8109cad8>] process_one_work+0x168/0x480
[121025.880219]  [<ffffffff8109ce3b>] worker_thread+0x4b/0x500
[121025.880221]  [<ffffffff8109cdf0>] ? process_one_work+0x480/0x480
[121025.880222]  [<ffffffff810a3228>] kthread+0xd8/0xf0
[121025.880224]  [<ffffffff81840ae2>] ret_from_fork+0x22/0x40
[121025.880226]  [<ffffffff810a3150>] ? kthread_create_on_node+0x1a0/0x1a0
[121025.880228] Mem-Info:
[121025.880230] active_anon:18131 inactive_anon:23781 isolated_anon:0
                 active_file:84105 inactive_file:84587 isolated_file:19
                 unevictable:1762 dirty:869 writeback:23497 unstable:0
                 slab_reclaimable:25801 slab_unreclaimable:5224
                 mapped:33650 shmem:34217 pagetables:1605 bounce:0
                 free:1897 free_pcp:21 free_cma:0
[121025.880232] Node 0 DMA free:3920kB min:60kB low:72kB high:84kB active_anon:188kB inactive_anon:1324kB active_file:2540kB inactive_file:2664kB unevictable:112kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlocked:112kB dirty:0kB writeback:80kB mapped:884kB shmem:1356kB slab_reclaimable:2296kB slab_unreclaimable:284kB kernel_stack:64kB pagetables:80kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[121025.880236] lowmem_reserve[]: 0 973 973 973 973
[121025.880239] Node 0 DMA32 free:3668kB min:3824kB low:4820kB high:5816kB active_anon:72336kB inactive_anon:93800kB active_file:333880kB inactive_file:335684kB unevictable:6936kB isolated(anon):0kB isolated(file):76kB present:1032184kB managed:1000480kB mlocked:6936kB dirty:3476kB writeback:93908kB mapped:133716kB shmem:135512kB slab_reclaimable:100908kB slab_unreclaimable:20612kB kernel_stack:3296kB pagetables:6340kB unstable:0kB bounce:0kB free_pcp:84kB local_pcp:84kB free_cma:0kB writeback_tmp:0kB pages_scanned:160 all_unreclaimable? no
[121025.880242] lowmem_reserve[]: 0 0 0 0 0
[121025.880244] Node 0 DMA: 361*4kB (UME) 59*8kB (UEH) 1*16kB (H) 0*32kB 1*64kB (H) 1*128kB (H) 1*256kB (H) 1*512kB (H) 1*1024kB (H) 0*2048kB 0*4096kB = 3916kB
[121025.880251] Node 0 DMA32: 836*4kB (UMH) 22*8kB (UH) 16*16kB (H) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 3776kB
[121025.880258] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[121025.880258] 204488 total pagecache pages
[121025.880259] 675 pages in swap cache
[121025.880260] Swap cache stats: add 42167, delete 41492, find 1069663/1070758
[121025.880261] Free swap  = 897344kB
[121025.880261] Total swap = 1046524kB
[121025.880262] 262044 pages RAM
[121025.880262] 0 pages HighMem/MovableOnly
[121025.880263] 7947 pages reserved
[121025.880264] 0 pages cma reserved
[121025.880266] 0 pages hwpoisoned
[121025.880267] SLUB: Unable to allocate memory on node -1, gfp=0x2080020(GFP_ATOMIC)
[121025.880268]   cache: kmalloc-256, object size: 256, buffer size: 256, default order: 0, min order: 0
[121025.880269]   node 0: slabs: 148, objs: 2368, free: 0