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Date:	Fri, 29 Apr 2011 00:40:38 +0200
From:	Jan Kara <jack@...e.cz>
To:	Colin Ian King <colin.king@...ntu.com>
Cc:	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	James Bottomley <james.bottomley@...e.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>, mgorman@...ell.com
Subject: Re: [BUG] fatal hang untarring 90GB file, possibly writeback
 related.

On Thu 28-04-11 15:58:21, Colin Ian King wrote:
> On Thu, 2011-04-28 at 16:33 +0200, Jan Kara wrote:
> > On Thu 28-04-11 16:25:51, Jan Kara wrote:
> > > On Thu 28-04-11 15:01:22, Colin Ian King wrote:
> > > > 
> > > > > Could you post the soft lockups you're seeing?
> > > > 
> > > > As requested, attached
> > >   Hum, what keeps puzzling me is that in all the cases of hangs I've seen
> > > so far, we are stuck waiting for IO to finish for a long time - e.g. in the
> > > traces below kjournald waits for PageWriteback bit to get cleared. Also we
> > > are stuck waiting for page locks which might be because those pages are
> > > being read in? All in all it seems that the IO is just incredibly slow.
> > > 
> > > But it's not clear to me what pushes us into that situation (especially
> > > since ext4 refuses to do any IO from ->writepage (i.e. kswapd) when the
> > > underlying blocks are not already allocated.
> >   Hmm, maybe because the system is under memory pressure (and kswapd is not
> > able to get rid of dirty pages), we page out clean pages. Thus also pages
> > of executables which need to be paged in soon anyway thus putting heavy
> > read load on the system which makes writes crawl? I'm not sure why
> > compaction should make this any worse but maybe it can.
> > 
> > James, Colin, can you capture output of 'vmstat 1' while you do the
> > copying? Thanks.
> 
> Attached.
  Thanks. So I there are a few interesting points in the vmstat output:
For first 30 seconds, we are happily copying data - relatively steady read
throughput (about 20-40 MB/s) and occasional peak from flusher thread
flushing dirty data. During this time free memory drops from about 1.4 GB
to about 22!!! MB - mm seems to like to really use the machine ;). Then
things get interesting:
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 0  1      0  83372   5228 1450776    0    0 39684 90132  450  918  0  4 74 22
 0  1      0  22416   5228 1509864    0    0 29452 48492  403  869  1  2 80 18
 2  0      0  20056   5384 1513996    0    0  2248  2116  434 1191  4  4 71 21
 0  1      0  19800   5932 1514600    0    0   644   104  454 1166  8  3 64 24
 1  0      0  21848   5940 1515244    0    0   292   380  468 1775 15  6 75 3
 1  0      0  20936   5940 1515876    0    0   296   296  496 1846 18  8 74 0
 1  0      0  17792   5940 1516580    0    0   356   356  484 1862 23  8 69 0
 1  0      0  17544   5940 1517364    0    0   412   412  482 1812 16  7 77 0
 4  0      0  18148   5948 1517968    0    0   288   344  436 1749 19  9 69 3
 0  2    220 137528   1616 1402468    0  220 74708  2164  849 1806  3  6 63 28
 0  3    224  36184   1628 1499648    0    4 50820 86204  532 1272  0  4 64 32
 0  2  19680  53688   1628 1484388   32 19456  6080 62972  242  287  0  2 63 34
 0  2  36928 1407432   1356 150980    0 17252  1564 17276  368  764  1  3 73 22

So when free memory reached about 20 MB, both read and write activity
almost stalled for 7 s (probably everybody waits for free memory). Then
mm manages to free 100 MB from page cache, things move on for two seconds,
then we swap out! about 36 MB and page reclaim also finally decides it
maybe has too much of page cache and reaps most of it (1.3 GB in one go).
Then things get going again, although there are still occasional stalls
such as this (about 30s later):
 1  3  36688 753192   1208 792344    0    0 35948 32768  435 6625  0  6 61 33
 0  2  36668 754996   1344 792760    0    0   252 58736 2832 16239  0  1 60 39
 0  2  36668 750132   1388 796688    0    0  2508  1524  325  959  1  3 68 28
 1  0  36668 751160   1400 797968    0    0   620   620  460 1470  6  6 50 38
 1  0  36668 750516   1400 798520    0    0   300   300  412 1764 17  8 75 1
 1  0  36668 750648   1408 799108    0    0   280   340  423 1816 18  6 73 3
 1  0  36668 748856   1408 799752    0    0   336   328  409 1788 18  8 75 0
 1  0  36668 748120   1416 800604    0    0   428   452  407 1723 14 10 75 2
 1  0  36668 750048   1416 801176    0    0   296   296  405 1779 18  7 75 1
 0  1  36668 650428   1420 897252    0    0 48100   556  658 1718 10  3 71 15
 0  2  36668 505444   1424 1037012    0    0 69888 90272  686 1491  1  4 68 27
 0  1  36668 479264   1428 1063372    0    0 12984 40896  324  674  1  1 76 23
...
I'm not sure what we were blocked on here since there is still plenty of
free memory (750 MB). These stalls repeat once in a while but things go on.
Then at about 350s, things just stop:
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 3  1  75280  73564   1844 1503848    0    0 43396 81976  627 1061  0 25 42 32
 3  3  75280  73344   1852 1504256    0    0   256    20  240  149  0 26 25 49
 3  3  75280  73344   1852 1504268    0    0     0     0  265  140  0 29 13 58
 3  3  75280  73468   1852 1504232    0    0     0     0  265  132  0 22 34 44
 3  3  75280  73468   1852 1504232    0    0     0     0  339  283  0 25 26 49
 3  3  75280  73468   1852 1504232    0    0     0     0  362  327  0 25 25 50
 3  3  75280  73468   1852 1504232    0    0     0     0  317  320  0 26 25 49
 3  3  75280  73468   1852 1504232    0    0     0     0  361  343  0 26 25 50

and nothing really happens for 150 s, except more and more tasks blocking
in D state (second column).
 3  6  75272  73416   1872 1503872    0    0     0     0  445  700  0 25 25 50
 0  7  75264  67940   1884 1509008   64    0  5056    16  481  876  0 22 23 55
Then suddently things get going again:
 0  2  75104  76808   1892 1502552  352    0 14292 40456  459 14865  0  2 39 59
 0  1  75104  75704   1900 1503412    0    0   820    32  405  788  1  1 72 27
 1  0  75104  76512   1904 1505576    0    0  1068  1072  454 1586  8  7 74 11

I guess this 150 s stall is when kernel barfs the "task blocked for more
than 30 seconds" messages. And from the traces we know that everyone is
waiting for PageWriteback or page lock during this time. Also James's vmstat
report shows that IO is stalled when kswapd is spinning. Really strange.

James in the meantime identified that cgroups are somehow involved. Are you
using systemd by any chance? Maybe cgroup IO throttling screws us?

								Honza

> > > [  287.088371] INFO: task rs:main Q:Reg:749 blocked for more than 30 seconds.
> > > [  287.088374] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > [  287.088376] rs:main Q:Reg   D 0000000000000000     0   749      1 0x00000000
> > > [  287.088381]  ffff880072c17b68 0000000000000082 ffff880072c17fd8 ffff880072c16000
> > > [  287.088392]  0000000000013d00 ffff88003591b178 ffff880072c17fd8 0000000000013d00
> > > [  287.088396]  ffffffff81a0b020 ffff88003591adc0 ffff88001fffc3e8 ffff88001fc13d00
> > > [  287.088400] Call Trace:
> > > [  287.088404]  [<ffffffff8110c070>] ? sync_page+0x0/0x50
> > > [  287.088408]  [<ffffffff815c0990>] io_schedule+0x70/0xc0
> > > [  287.088411]  [<ffffffff8110c0b0>] sync_page+0x40/0x50
> > > [  287.088414]  [<ffffffff815c130f>] __wait_on_bit+0x5f/0x90
> > > [  287.088418]  [<ffffffff8110c278>] wait_on_page_bit+0x78/0x80
> > > [  287.088421]  [<ffffffff81087f70>] ? wake_bit_function+0x0/0x50
> > > [  287.088425]  [<ffffffff8110dffd>] __lock_page_or_retry+0x3d/0x70
> > > [  287.088428]  [<ffffffff8110e3c7>] filemap_fault+0x397/0x4a0
> > > [  287.088431]  [<ffffffff8112d144>] __do_fault+0x54/0x520
> > > [  287.088434]  [<ffffffff81134a43>] ? unmap_region+0x113/0x170
> > > [  287.088437]  [<ffffffff812ded90>] ? prio_tree_insert+0x150/0x1c0
> > > [  287.088440]  [<ffffffff811309da>] handle_pte_fault+0xfa/0x210
> > > [  287.088442]  [<ffffffff810442a7>] ? pte_alloc_one+0x37/0x50
> > > [  287.088446]  [<ffffffff815c2cce>] ? _raw_spin_lock+0xe/0x20
> > > [  287.088448]  [<ffffffff8112de25>] ? __pte_alloc+0xb5/0x100
> > > [  287.088451]  [<ffffffff81131d5d>] handle_mm_fault+0x16d/0x250
> > > [  287.088454]  [<ffffffff815c6a47>] do_page_fault+0x1a7/0x540
> > > [  287.088457]  [<ffffffff81136f85>] ? do_mmap_pgoff+0x335/0x370
> > > [  287.088460]  [<ffffffff81137127>] ? sys_mmap_pgoff+0x167/0x230
> > > [  287.088463]  [<ffffffff815c34d5>] page_fault+0x25/0x30
> > > [  287.088466] INFO: task NetworkManager:764 blocked for more than 30 seconds.
> > > [  287.088468] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > [  287.088470] NetworkManager  D 0000000000000002     0   764      1 0x00000000
> > > [  287.088473]  ffff880074ffbb68 0000000000000082 ffff880074ffbfd8 ffff880074ffa000
> > > [  287.088477]  0000000000013d00 ffff880036051a98 ffff880074ffbfd8 0000000000013d00
> > > [  287.088481]  ffff8801005badc0 ffff8800360516e0 ffff88001ffef128 ffff88001fc53d00
> > > [  287.088484] Call Trace:
> > > [  287.088488]  [<ffffffff8110c070>] ? sync_page+0x0/0x50
> > > [  287.088491]  [<ffffffff815c0990>] io_schedule+0x70/0xc0
> > > [  287.088494]  [<ffffffff8110c0b0>] sync_page+0x40/0x50
> > > [  287.088497]  [<ffffffff815c130f>] __wait_on_bit+0x5f/0x90
> > > [  287.088500]  [<ffffffff8110c278>] wait_on_page_bit+0x78/0x80
> > > [  287.088503]  [<ffffffff81087f70>] ? wake_bit_function+0x0/0x50
> > > [  287.088506]  [<ffffffff8110dffd>] __lock_page_or_retry+0x3d/0x70
> > > [  287.088509]  [<ffffffff8110e3c7>] filemap_fault+0x397/0x4a0
> > > [  287.088513]  [<ffffffff81177110>] ? pollwake+0x0/0x60
> > > [  287.088516]  [<ffffffff8112d144>] __do_fault+0x54/0x520
> > > [  287.088519]  [<ffffffff81177110>] ? pollwake+0x0/0x60
> > > [  287.088522]  [<ffffffff811309da>] handle_pte_fault+0xfa/0x210
> > > [  287.088525]  [<ffffffff8111561d>] ? __free_pages+0x2d/0x40
> > > [  287.088527]  [<ffffffff8112de4f>] ? __pte_alloc+0xdf/0x100
> > > [  287.088530]  [<ffffffff81131d5d>] handle_mm_fault+0x16d/0x250
> > > [  287.088533]  [<ffffffff815c6a47>] do_page_fault+0x1a7/0x540
> > > [  287.088537]  [<ffffffff81013859>] ? read_tsc+0x9/0x20
> > > [  287.088540]  [<ffffffff81092eb1>] ? ktime_get_ts+0xb1/0xf0
> > > [  287.088543]  [<ffffffff811776d2>] ? poll_select_set_timeout+0x82/0x90
> > > [  287.088546]  [<ffffffff815c34d5>] page_fault+0x25/0x30
> > > [  287.088559] INFO: task unity-panel-ser:1521 blocked for more than 30 seconds.
> > > [  287.088561] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > [  287.088562] unity-panel-ser D 0000000000000000     0  1521      1 0x00000000
> > > [  287.088566]  ffff880061f37b68 0000000000000082 ffff880061f37fd8 ffff880061f36000
> > > [  287.088570]  0000000000013d00 ffff880068c7c858 ffff880061f37fd8 0000000000013d00
> > > [  287.088573]  ffff88003591c4a0 ffff880068c7c4a0 ffff88001fff0c88 ffff88001fc13d00
> > > [  287.088577] Call Trace:
> > > [  287.088581]  [<ffffffff8110c070>] ? sync_page+0x0/0x50
> > > [  287.088583]  [<ffffffff815c0990>] io_schedule+0x70/0xc0
> > > [  287.088587]  [<ffffffff8110c0b0>] sync_page+0x40/0x50
> > > [  287.088589]  [<ffffffff815c130f>] __wait_on_bit+0x5f/0x90
> > > [  287.088593]  [<ffffffff8110c278>] wait_on_page_bit+0x78/0x80
> > > [  287.088596]  [<ffffffff81087f70>] ? wake_bit_function+0x0/0x50
> > > [  287.088599]  [<ffffffff8110dffd>] __lock_page_or_retry+0x3d/0x70
> > > [  287.088602]  [<ffffffff8110e3c7>] filemap_fault+0x397/0x4a0
> > > [  287.088605]  [<ffffffff8112d144>] __do_fault+0x54/0x520
> > > [  287.088608]  [<ffffffff811309da>] handle_pte_fault+0xfa/0x210
> > > [  287.088610]  [<ffffffff8111561d>] ? __free_pages+0x2d/0x40
> > > [  287.088613]  [<ffffffff8112de4f>] ? __pte_alloc+0xdf/0x100
> > > [  287.088616]  [<ffffffff81131d5d>] handle_mm_fault+0x16d/0x250
> > > [  287.088619]  [<ffffffff815c6a47>] do_page_fault+0x1a7/0x540
> > > [  287.088622]  [<ffffffff81136f85>] ? do_mmap_pgoff+0x335/0x370
> > > [  287.088625]  [<ffffffff815c34d5>] page_fault+0x25/0x30
> > > [  287.088629] INFO: task jbd2/sda4-8:1845 blocked for more than 30 seconds.
> > > [  287.088630] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > [  287.088632] jbd2/sda4-8     D 0000000000000000     0  1845      2 0x00000000
> > > [  287.088636]  ffff880068f6baf0 0000000000000046 ffff880068f6bfd8 ffff880068f6a000
> > > [  287.088639]  0000000000013d00 ffff880061d603b8 ffff880068f6bfd8 0000000000013d00
> > > [  287.088643]  ffff88003591c4a0 ffff880061d60000 ffff88001fff8548 ffff88001fc13d00
> > > [  287.088647] Call Trace:
> > > [  287.088650]  [<ffffffff8110c070>] ? sync_page+0x0/0x50
> > > [  287.088653]  [<ffffffff815c0990>] io_schedule+0x70/0xc0
> > > [  287.088656]  [<ffffffff8110c0b0>] sync_page+0x40/0x50
> > > [  287.088659]  [<ffffffff815c130f>] __wait_on_bit+0x5f/0x90
> > > [  287.088662]  [<ffffffff8110c278>] wait_on_page_bit+0x78/0x80
> > > [  287.088665]  [<ffffffff81087f70>] ? wake_bit_function+0x0/0x50
> > > [  287.088668]  [<ffffffff8110c41d>] filemap_fdatawait_range+0xfd/0x190
> > > [  287.088672]  [<ffffffff8110c4db>] filemap_fdatawait+0x2b/0x30
> > > [  287.088675]  [<ffffffff81242a93>] journal_finish_inode_data_buffers+0x63/0x170
> > > [  287.088678]  [<ffffffff81243284>] jbd2_journal_commit_transaction+0x6e4/0x1190
> > > [  287.088682]  [<ffffffff81076185>] ? try_to_del_timer_sync+0x85/0xe0
> > > [  287.088685]  [<ffffffff81247e9b>] kjournald2+0xbb/0x220
> > > [  287.088688]  [<ffffffff81087f30>] ? autoremove_wake_function+0x0/0x40
> > > [  287.088691]  [<ffffffff81247de0>] ? kjournald2+0x0/0x220
> > > [  287.088694]  [<ffffffff810877e6>] kthread+0x96/0xa0
> > > [  287.088697]  [<ffffffff8100ce24>] kernel_thread_helper+0x4/0x10
> > > [  287.088700]  [<ffffffff81087750>] ? kthread+0x0/0xa0
> > > [  287.088703]  [<ffffffff8100ce20>] ? kernel_thread_helper+0x0/0x10
> > > [  287.088705] INFO: task dirname:5969 blocked for more than 30 seconds.
> > > [  287.088707] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > [  287.088709] dirname         D 0000000000000002     0  5969   5214 0x00000000
> > > [  287.088712]  ffff88005bd9d8b8 0000000000000086 ffff88005bd9dfd8 ffff88005bd9c000
> > > [  287.088716]  0000000000013d00 ffff88005d65b178 ffff88005bd9dfd8 0000000000013d00
> > > [  287.088720]  ffff8801005e5b80 ffff88005d65adc0 ffff88001ffe5228 ffff88001fc53d00
> > > [  287.088723] Call Trace:
> > > [  287.088726]  [<ffffffff8110c070>] ? sync_page+0x0/0x50
> > > [  287.088729]  [<ffffffff815c0990>] io_schedule+0x70/0xc0
> > > [  287.088732]  [<ffffffff8110c0b0>] sync_page+0x40/0x50
> > > [  287.088735]  [<ffffffff815c130f>] __wait_on_bit+0x5f/0x90
> > > [  287.088738]  [<ffffffff8110c278>] wait_on_page_bit+0x78/0x80
> > > [  287.088741]  [<ffffffff81087f70>] ? wake_bit_function+0x0/0x50
> > > [  287.088744]  [<ffffffff8110dffd>] __lock_page_or_retry+0x3d/0x70
> > > [  287.088747]  [<ffffffff8110e3c7>] filemap_fault+0x397/0x4a0
> > > [  287.088750]  [<ffffffff8112d144>] __do_fault+0x54/0x520
> > > [  287.088753]  [<ffffffff811309da>] handle_pte_fault+0xfa/0x210
> > > [  287.088756]  [<ffffffff810442a7>] ? pte_alloc_one+0x37/0x50
> > > [  287.088759]  [<ffffffff815c2cce>] ? _raw_spin_lock+0xe/0x20
> > > [  287.088761]  [<ffffffff8112de25>] ? __pte_alloc+0xb5/0x100
> > > [  287.088764]  [<ffffffff81131d5d>] handle_mm_fault+0x16d/0x250
> > > [  287.088767]  [<ffffffff815c6a47>] do_page_fault+0x1a7/0x540
> > > [  287.088770]  [<ffffffff81136947>] ? mmap_region+0x1f7/0x500
> > > [  287.088773]  [<ffffffff8112db06>] ? free_pgd_range+0x356/0x4a0
> > > [  287.088776]  [<ffffffff815c34d5>] page_fault+0x25/0x30
> > > [  287.088779]  [<ffffffff812e6d5f>] ? __clear_user+0x3f/0x70
> > > [  287.088782]  [<ffffffff812e6d41>] ? __clear_user+0x21/0x70
> > > [  287.088786]  [<ffffffff812e6dc6>] clear_user+0x36/0x40
> > > [  287.088788]  [<ffffffff811b0b6d>] padzero+0x2d/0x40
> > > [  287.088791]  [<ffffffff811b2c7a>] load_elf_binary+0x95a/0xe00
> > > [  287.088794]  [<ffffffff8116aa8a>] search_binary_handler+0xda/0x300
> > > [  287.088797]  [<ffffffff811b2320>] ? load_elf_binary+0x0/0xe00
> > > [  287.088800]  [<ffffffff8116c49c>] do_execve+0x24c/0x2d0
> > > [  287.088802]  [<ffffffff8101521a>] sys_execve+0x4a/0x80
> > > [  287.088805]  [<ffffffff8100c45c>] stub_execve+0x6c/0xc0
> > > -- 
> > > Jan Kara <jack@...e.cz>
> > > SUSE Labs, CR
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> > > the body of a message to majordomo@...r.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 


-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
--
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