Groups > linux.kernel > #1334776 > unrolled thread

Re: [PATCH 0/3] OOM detection rework v4

Started by	Michal Hocko <mhocko@kernel.org>
First post	2016-02-15 21:10 +0100
Last post	2016-02-16 16:20 +0100
Articles	3 — 2 participants

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  Re: [PATCH 0/3] OOM detection rework v4 Michal Hocko <mhocko@kernel.org> - 2016-02-15 21:10 +0100
    Re: [PATCH 0/3] OOM detection rework v4 Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-02-16 14:20 +0100
      Re: [PATCH 0/3] OOM detection rework v4 Michal Hocko <mhocko@kernel.org> - 2016-02-16 16:20 +0100

#1334776 — Re: [PATCH 0/3] OOM detection rework v4

From	Michal Hocko <mhocko@kernel.org>
Date	2016-02-15 21:10 +0100
Subject	Re: [PATCH 0/3] OOM detection rework v4
Message-ID	<r2xD4-5Wh-5@gated-at.bofh.it>

On Sun 07-02-16 13:09:33, Tetsuo Handa wrote:
[...]
> FYI, I again hit unexpected OOM-killer during genxref on linux-4.5-rc2 source.
> I think current patchset is too fragile to merge.
> ----------------------------------------
> [ 3101.626995] smbd invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
> [ 3101.629148] smbd cpuset=/ mems_allowed=0
[...]
> [ 3101.705887] Node 0 DMA: 75*4kB (UME) 69*8kB (UME) 43*16kB (UM) 23*32kB (UME) 8*64kB (UM) 4*128kB (UME) 2*256kB (UM) 0*512kB 1*1024kB (U) 1*2048kB (M) 0*4096kB = 6884kB
> [ 3101.710581] Node 0 DMA32: 4513*4kB (UME) 15*8kB (U) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 18172kB

How come this is an unexpected OOM? There is clearly no order-2+ page
available for the allocation request.

> > Something like the following:
> Yes, I do think we need something like it.

Was the patch applied?

-- 
Michal Hocko
SUSE Labs

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#1335367

From	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date	2016-02-16 14:20 +0100
Message-ID	<r2NHR-8jx-27@gated-at.bofh.it>
In reply to	#1334776

Michal Hocko wrote:
> On Sun 07-02-16 13:09:33, Tetsuo Handa wrote:
> [...]
> > FYI, I again hit unexpected OOM-killer during genxref on linux-4.5-rc2 source.
> > I think current patchset is too fragile to merge.
> > ----------------------------------------
> > [ 3101.626995] smbd invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
> > [ 3101.629148] smbd cpuset=/ mems_allowed=0
> [...]
> > [ 3101.705887] Node 0 DMA: 75*4kB (UME) 69*8kB (UME) 43*16kB (UM) 23*32kB (UME) 8*64kB (UM) 4*128kB (UME) 2*256kB (UM) 0*512kB 1*1024kB (U) 1*2048kB (M) 0*4096kB = 6884kB
> > [ 3101.710581] Node 0 DMA32: 4513*4kB (UME) 15*8kB (U) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 18172kB
> 
> How come this is an unexpected OOM? There is clearly no order-2+ page
> available for the allocation request.

I used "unexpected" because there were only 35 userspace processes and
genxref was the only process which did a lot of memory allocation
(modulo kernel threads woken by file I/O) and most memory is reclaimable.

> 
> > > Something like the following:
> > Yes, I do think we need something like it.
> 
> Was the patch applied?

No for above result.

A result with the patch (20160204142400.GC14425@dhcp22.suse.cz) applied on
today's linux-next is shown below. It seems that protection is not enough.

----------
[  118.584571] fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
[  118.586684] fork cpuset=/ mems_allowed=0
[  118.588254] CPU: 2 PID: 9565 Comm: fork Not tainted 4.5.0-rc4-next-20160216+ #306
[  118.589795] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[  118.591941]  0000000000000286 0000000085a9ed62 ffff88007b3d3ad0 ffffffff8139e82d
[  118.593616]  0000000000000000 ffff88007b3d3d00 ffff88007b3d3b70 ffffffff811bedec
[  118.595273]  0000000000000206 ffffffff81810b70 ffff88007b3d3b10 ffffffff810be8f9
[  118.596970] Call Trace:
[  118.597634]  [<ffffffff8139e82d>] dump_stack+0x85/0xc8
[  118.598787]  [<ffffffff811bedec>] dump_header+0x5b/0x3b0
[  118.599979]  [<ffffffff810be8f9>] ? trace_hardirqs_on_caller+0xf9/0x1c0
[  118.601421]  [<ffffffff810be9cd>] ? trace_hardirqs_on+0xd/0x10
[  118.602713]  [<ffffffff811447f6>] oom_kill_process+0x366/0x550
[  118.604882]  [<ffffffff81144c1f>] out_of_memory+0x1ef/0x5a0
[  118.606940]  [<ffffffff81144cdd>] ? out_of_memory+0x2ad/0x5a0
[  118.608275]  [<ffffffff8114a63b>] __alloc_pages_nodemask+0xb3b/0xd80
[  118.609698]  [<ffffffff810be800>] ? mark_held_locks+0x90/0x90
[  118.611166]  [<ffffffff8114aa3c>] alloc_kmem_pages_node+0x4c/0xc0
[  118.612589]  [<ffffffff8106d661>] copy_process.part.33+0x131/0x1be0
[  118.614203]  [<ffffffff8111e20a>] ? __audit_syscall_entry+0xaa/0xf0
[  118.615689]  [<ffffffff810e8939>] ? current_kernel_time64+0xa9/0xc0
[  118.617151]  [<ffffffff8106f2db>] _do_fork+0xdb/0x5d0
[  118.618391]  [<ffffffff810030c1>] ? do_audit_syscall_entry+0x61/0x70
[  118.619875]  [<ffffffff81003254>] ? syscall_trace_enter_phase1+0x134/0x150
[  118.621642]  [<ffffffff810bae1a>] ? up_read+0x1a/0x40
[  118.622920]  [<ffffffff817093ce>] ? retint_user+0x18/0x23
[  118.624262]  [<ffffffff810035ec>] ? do_syscall_64+0x1c/0x180
[  118.625661]  [<ffffffff8106f854>] SyS_clone+0x14/0x20
[  118.626959]  [<ffffffff8100362d>] do_syscall_64+0x5d/0x180
[  118.628340]  [<ffffffff81708abf>] entry_SYSCALL64_slow_path+0x25/0x25
[  118.630002] Mem-Info:
[  118.630853] active_anon:27270 inactive_anon:2094 isolated_anon:0
[  118.630853]  active_file:253575 inactive_file:89021 isolated_file:22
[  118.630853]  unevictable:0 dirty:0 writeback:0 unstable:0
[  118.630853]  slab_reclaimable:14202 slab_unreclaimable:13906
[  118.630853]  mapped:1622 shmem:2162 pagetables:10587 bounce:0
[  118.630853]  free:5328 free_pcp:356 free_cma:0
[  118.639774] Node 0 DMA free:6904kB min:44kB low:52kB high:64kB active_anon:3280kB inactive_anon:156kB active_file:684kB inactive_file:2292kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15988kB managed:15904kB mlocked:0kB dirty:0kB writeback:0kB mapped:420kB shmem:164kB slab_reclaimable:564kB slab_unreclaimable:800kB kernel_stack:256kB pagetables:200kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[  118.650132] lowmem_reserve[]: 0 1714 1714 1714
[  118.651763] Node 0 DMA32 free:14256kB min:5172kB low:6464kB high:7756kB active_anon:105924kB inactive_anon:8220kB active_file:1026268kB inactive_file:340844kB unevictable:0kB isolated(anon):0kB isolated(file):88kB present:2080640kB managed:1759460kB mlocked:0kB dirty:0kB writeback:0kB mapped:6436kB shmem:8484kB slab_reclaimable:56740kB slab_unreclaimable:54824kB kernel_stack:28112kB pagetables:42148kB unstable:0kB bounce:0kB free_pcp:1440kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[  118.663101] lowmem_reserve[]: 0 0 0 0
[  118.664704] Node 0 DMA: 83*4kB (ME) 51*8kB (UME) 9*16kB (UME) 2*32kB (UM) 1*64kB (M) 4*128kB (UME) 5*256kB (UME) 2*512kB (UM) 1*1024kB (E) 1*2048kB (M) 0*4096kB = 6900kB
[  118.670166] Node 0 DMA32: 2327*4kB (ME) 621*8kB (M) 1*16kB (M) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 14292kB
[  118.673742] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
[  118.676297] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[  118.678610] 344508 total pagecache pages
[  118.680163] 0 pages in swap cache
[  118.681567] Swap cache stats: add 0, delete 0, find 0/0
[  118.681567] Free swap  = 0kB
[  118.681568] Total swap = 0kB
[  118.681625] 524157 pages RAM
[  118.681625] 0 pages HighMem/MovableOnly
[  118.681625] 80316 pages reserved
[  118.681626] 0 pages hwpoisoned

[  120.117093] fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
[  120.117097] fork cpuset=/ mems_allowed=0
[  120.117099] CPU: 0 PID: 9566 Comm: fork Not tainted 4.5.0-rc4-next-20160216+ #306
[  120.117100] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[  120.117102]  0000000000000286 00000000be6c9129 ffff880035dabad0 ffffffff8139e82d
[  120.117103]  0000000000000000 ffff880035dabd00 ffff880035dabb70 ffffffff811bedec
[  120.117104]  0000000000000206 ffffffff81810b70 ffff880035dabb10 ffffffff810be8f9
[  120.117104] Call Trace:
[  120.117111]  [<ffffffff8139e82d>] dump_stack+0x85/0xc8
[  120.117113]  [<ffffffff811bedec>] dump_header+0x5b/0x3b0
[  120.117116]  [<ffffffff810be8f9>] ? trace_hardirqs_on_caller+0xf9/0x1c0
[  120.117117]  [<ffffffff810be9cd>] ? trace_hardirqs_on+0xd/0x10
[  120.117119]  [<ffffffff811447f6>] oom_kill_process+0x366/0x550
[  120.117121]  [<ffffffff81144c1f>] out_of_memory+0x1ef/0x5a0
[  120.117122]  [<ffffffff81144cdd>] ? out_of_memory+0x2ad/0x5a0
[  120.117123]  [<ffffffff8114a63b>] __alloc_pages_nodemask+0xb3b/0xd80
[  120.117124]  [<ffffffff810be800>] ? mark_held_locks+0x90/0x90
[  120.117125]  [<ffffffff8114aa3c>] alloc_kmem_pages_node+0x4c/0xc0
[  120.117128]  [<ffffffff8106d661>] copy_process.part.33+0x131/0x1be0
[  120.117130]  [<ffffffff8111e20a>] ? __audit_syscall_entry+0xaa/0xf0
[  120.117132]  [<ffffffff810e8939>] ? current_kernel_time64+0xa9/0xc0
[  120.117133]  [<ffffffff8106f2db>] _do_fork+0xdb/0x5d0
[  120.117136]  [<ffffffff810030c1>] ? do_audit_syscall_entry+0x61/0x70
[  120.117137]  [<ffffffff81003254>] ? syscall_trace_enter_phase1+0x134/0x150
[  120.117139]  [<ffffffff810bae1a>] ? up_read+0x1a/0x40
[  120.117142]  [<ffffffff817093ce>] ? retint_user+0x18/0x23
[  120.117143]  [<ffffffff810035ec>] ? do_syscall_64+0x1c/0x180
[  120.117144]  [<ffffffff8106f854>] SyS_clone+0x14/0x20
[  120.117145]  [<ffffffff8100362d>] do_syscall_64+0x5d/0x180
[  120.117147]  [<ffffffff81708abf>] entry_SYSCALL64_slow_path+0x25/0x25
[  120.117147] Mem-Info:
[  120.117150] active_anon:30895 inactive_anon:2094 isolated_anon:0
[  120.117150]  active_file:183306 inactive_file:118692 isolated_file:18
[  120.117150]  unevictable:0 dirty:47 writeback:0 unstable:0
[  120.117150]  slab_reclaimable:14405 slab_unreclaimable:22372
[  120.117150]  mapped:3101 shmem:2162 pagetables:20154 bounce:0
[  120.117150]  free:7231 free_pcp:108 free_cma:0
[  120.117154] Node 0 DMA free:6904kB min:44kB low:52kB high:64kB active_anon:1172kB inactive_anon:156kB active_file:684kB inactive_file:1356kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15988kB managed:15904kB mlocked:0kB dirty:0kB writeback:0kB mapped:420kB shmem:164kB slab_reclaimable:564kB slab_unreclaimable:2244kB kernel_stack:1376kB pagetables:436kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:4 all_unreclaimable? no
[  120.117156] lowmem_reserve[]: 0 1714 1714 1714
[  120.117172] Node 0 DMA32 free:22020kB min:5172kB low:6464kB high:7756kB active_anon:122408kB inactive_anon:8220kB active_file:732540kB inactive_file:473412kB unevictable:0kB isolated(anon):0kB isolated(file):72kB present:2080640kB managed:1759460kB mlocked:0kB dirty:188kB writeback:0kB mapped:11984kB shmem:8484kB slab_reclaimable:57056kB slab_unreclaimable:87244kB kernel_stack:52048kB pagetables:80180kB unstable:0kB bounce:0kB free_pcp:432kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[  120.117230] lowmem_reserve[]: 0 0 0 0
[  120.117238] Node 0 DMA: 46*4kB (UME) 82*8kB (ME) 37*16kB (UME) 13*32kB (M) 3*64kB (UM) 2*128kB (ME) 2*256kB (ME) 2*512kB (UM) 1*1024kB (E) 1*2048kB (M) 0*4096kB = 6904kB
[  120.117242] Node 0 DMA32: 709*4kB (UME) 2374*8kB (UME) 0*16kB 10*32kB (E) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 22148kB
[  120.117244] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
[  120.117244] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[  120.117245] 304244 total pagecache pages
[  120.117246] 0 pages in swap cache
[  120.117246] Swap cache stats: add 0, delete 0, find 0/0
[  120.117247] Free swap  = 0kB
[  120.117247] Total swap = 0kB
[  120.117248] 524157 pages RAM
[  120.117248] 0 pages HighMem/MovableOnly
[  120.117248] 80316 pages reserved
[  120.117249] 0 pages hwpoisoned

[  126.034913] fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
[  126.034918] fork cpuset=/ mems_allowed=0
[  126.034920] CPU: 2 PID: 9566 Comm: fork Not tainted 4.5.0-rc4-next-20160216+ #306
[  126.034921] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[  126.034923]  0000000000000286 00000000be6c9129 ffff880035dabad0 ffffffff8139e82d
[  126.034925]  0000000000000000 ffff880035dabd00 ffff880035dabb70 ffffffff811bedec
[  126.034926]  0000000000000206 ffffffff81810b70 ffff880035dabb10 ffffffff810be8f9
[  126.034926] Call Trace:
[  126.034932]  [<ffffffff8139e82d>] dump_stack+0x85/0xc8
[  126.034935]  [<ffffffff811bedec>] dump_header+0x5b/0x3b0
[  126.034938]  [<ffffffff810be8f9>] ? trace_hardirqs_on_caller+0xf9/0x1c0
[  126.034939]  [<ffffffff810be9cd>] ? trace_hardirqs_on+0xd/0x10
[  126.034941]  [<ffffffff811447f6>] oom_kill_process+0x366/0x550
[  126.034943]  [<ffffffff81144c1f>] out_of_memory+0x1ef/0x5a0
[  126.034944]  [<ffffffff81144cdd>] ? out_of_memory+0x2ad/0x5a0
[  126.034945]  [<ffffffff8114a63b>] __alloc_pages_nodemask+0xb3b/0xd80
[  126.034947]  [<ffffffff810be800>] ? mark_held_locks+0x90/0x90
[  126.034948]  [<ffffffff8114aa3c>] alloc_kmem_pages_node+0x4c/0xc0
[  126.034950]  [<ffffffff8106d661>] copy_process.part.33+0x131/0x1be0
[  126.034952]  [<ffffffff8111e20a>] ? __audit_syscall_entry+0xaa/0xf0
[  126.034954]  [<ffffffff810e8939>] ? current_kernel_time64+0xa9/0xc0
[  126.034956]  [<ffffffff8106f2db>] _do_fork+0xdb/0x5d0
[  126.034958]  [<ffffffff810030c1>] ? do_audit_syscall_entry+0x61/0x70
[  126.034959]  [<ffffffff81003254>] ? syscall_trace_enter_phase1+0x134/0x150
[  126.034961]  [<ffffffff810bae1a>] ? up_read+0x1a/0x40
[  126.034965]  [<ffffffff817093ce>] ? retint_user+0x18/0x23
[  126.034965]  [<ffffffff810035ec>] ? do_syscall_64+0x1c/0x180
[  126.034967]  [<ffffffff8106f854>] SyS_clone+0x14/0x20
[  126.034968]  [<ffffffff8100362d>] do_syscall_64+0x5d/0x180
[  126.034969]  [<ffffffff81708abf>] entry_SYSCALL64_slow_path+0x25/0x25
[  126.034970] Mem-Info:
[  126.034973] active_anon:27060 inactive_anon:2093 isolated_anon:0
[  126.034973]  active_file:206123 inactive_file:85224 isolated_file:32
[  126.034973]  unevictable:0 dirty:47 writeback:0 unstable:0
[  126.034973]  slab_reclaimable:13214 slab_unreclaimable:26604
[  126.034973]  mapped:2421 shmem:2161 pagetables:24889 bounce:0
[  126.034973]  free:4649 free_pcp:30 free_cma:0
[  126.034986] Node 0 DMA free:6924kB min:44kB low:52kB high:64kB active_anon:1156kB inactive_anon:156kB active_file:728kB inactive_file:1060kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15988kB managed:15904kB mlocked:0kB dirty:0kB writeback:0kB mapped:368kB shmem:164kB slab_reclaimable:468kB slab_unreclaimable:2496kB kernel_stack:832kB pagetables:704kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:4 all_unreclaimable? no
[  126.034988] lowmem_reserve[]: 0 1714 1714 1714
[  126.034992] Node 0 DMA32 free:11672kB min:5172kB low:6464kB high:7756kB active_anon:107084kB inactive_anon:8216kB active_file:823764kB inactive_file:339836kB unevictable:0kB isolated(anon):0kB isolated(file):128kB present:2080640kB managed:1759460kB mlocked:0kB dirty:188kB writeback:0kB mapped:9316kB shmem:8480kB slab_reclaimable:52388kB slab_unreclaimable:103920kB kernel_stack:66016kB pagetables:98852kB unstable:0kB bounce:0kB free_pcp:120kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[  126.034993] lowmem_reserve[]: 0 0 0 0
[  126.035000] Node 0 DMA: 70*4kB (UME) 16*8kB (UME) 59*16kB (UME) 34*32kB (ME) 14*64kB (UME) 2*128kB (UE) 1*256kB (E) 2*512kB (M) 2*1024kB (ME) 0*2048kB 0*4096kB = 6920kB
[  126.035005] Node 0 DMA32: 2372*4kB (UME) 290*8kB (UM) 3*16kB (U) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 11856kB
[  126.035006] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
[  126.035006] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[  126.035007] 293674 total pagecache pages
[  126.035008] 0 pages in swap cache
[  126.035008] Swap cache stats: add 0, delete 0, find 0/0
[  126.035009] Free swap  = 0kB
[  126.035009] Total swap = 0kB
[  126.035010] 524157 pages RAM
[  126.035010] 0 pages HighMem/MovableOnly
[  126.035010] 80316 pages reserved
[  126.035011] 0 pages hwpoisoned
----------

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#1335515

From	Michal Hocko <mhocko@kernel.org>
Date	2016-02-16 16:20 +0100
Message-ID	<r2PzZ-18K-35@gated-at.bofh.it>
In reply to	#1335367

On Tue 16-02-16 22:10:01, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Sun 07-02-16 13:09:33, Tetsuo Handa wrote:
> > [...]
> > > FYI, I again hit unexpected OOM-killer during genxref on linux-4.5-rc2 source.
> > > I think current patchset is too fragile to merge.
> > > ----------------------------------------
> > > [ 3101.626995] smbd invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
> > > [ 3101.629148] smbd cpuset=/ mems_allowed=0
> > [...]
> > > [ 3101.705887] Node 0 DMA: 75*4kB (UME) 69*8kB (UME) 43*16kB (UM) 23*32kB (UME) 8*64kB (UM) 4*128kB (UME) 2*256kB (UM) 0*512kB 1*1024kB (U) 1*2048kB (M) 0*4096kB = 6884kB
> > > [ 3101.710581] Node 0 DMA32: 4513*4kB (UME) 15*8kB (U) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 18172kB
> > 
> > How come this is an unexpected OOM? There is clearly no order-2+ page
> > available for the allocation request.
> 
> I used "unexpected" because there were only 35 userspace processes and
> genxref was the only process which did a lot of memory allocation
> (modulo kernel threads woken by file I/O) and most memory is reclaimable.

The memory is reclaimable but that doesn't mean that order-2 page block
will get formed even if all of it gets reclaimed. The memory is simply
too fragmented. That is why I think the OOM makes sense.

> > > > Something like the following:
> > > Yes, I do think we need something like it.
> > 
> > Was the patch applied?
> 
> No for above result.
> 
> A result with the patch (20160204142400.GC14425@dhcp22.suse.cz) applied on
> today's linux-next is shown below. It seems that protection is not enough.
> 
> ----------
> [  118.584571] fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
[...]
> [  118.664704] Node 0 DMA: 83*4kB (ME) 51*8kB (UME) 9*16kB (UME) 2*32kB (UM) 1*64kB (M) 4*128kB (UME) 5*256kB (UME) 2*512kB (UM) 1*1024kB (E) 1*2048kB (M) 0*4096kB = 6900kB
> [  118.670166] Node 0 DMA32: 2327*4kB (ME) 621*8kB (M) 1*16kB (M) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 14292kB
[...]
> [  120.117093] fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
[...]
> [  120.117238] Node 0 DMA: 46*4kB (UME) 82*8kB (ME) 37*16kB (UME) 13*32kB (M) 3*64kB (UM) 2*128kB (ME) 2*256kB (ME) 2*512kB (UM) 1*1024kB (E) 1*2048kB (M) 0*4096kB = 6904kB
> [  120.117242] Node 0 DMA32: 709*4kB (UME) 2374*8kB (UME) 0*16kB 10*32kB (E) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 22148kB
[...]
> [  126.034913] fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
[...]
> [  126.035000] Node 0 DMA: 70*4kB (UME) 16*8kB (UME) 59*16kB (UME) 34*32kB (ME) 14*64kB (UME) 2*128kB (UE) 1*256kB (E) 2*512kB (M) 2*1024kB (ME) 0*2048kB 0*4096kB = 6920kB
> [  126.035005] Node 0 DMA32: 2372*4kB (UME) 290*8kB (UM) 3*16kB (U) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 11856kB

As you can see, in all cases we had order-2 requests and no order-2+
free blocks even after all the retries. I think the OOM is appropriate
at that time. We could have tried N+1 times but we have to draw a line
at some point of time. The reason why we do not have any high order
block available is a completely different question IMO. Maybe the
compaction just gets deferred and doesn't do anything. This would be
interesting to investigate further of course. Anyway my point is
that going OOM with the current fragmentation is simply the only choice.
-- 
Michal Hocko
SUSE Labs

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