Re: 100% iowait on one of cpus in current -git

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

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On Wed, Oct 31, 2007 at 04:22:10PM +0100, Torsten Kaiser wrote:
> On 10/22/07, Fengguang Wu <wfg@mail.ustc.edu.cn> wrote:
> > On Mon, Oct 22, 2007 at 09:10:45PM +0800, Fengguang Wu wrote:
> > > Hmm, Maybe it's an reiserfs related issue.  Do you have the full log file?
> >
> > Bingo! It can be reproduced in -mm on reiserfs:
> >
> > # mkfs.reiserfs /dev/sdb1
> > # mount /dev/sdb1 /test
> > # cp bin /test
> > <wait for a while>
> > # dmesg
> > [...]
> > [  418.346113] requeue_io 308: inode 6 size 302 at 08:11(sdb1)
> > [  418.346119] requeue_io 308: inode 7 size 196 at 08:11(sdb1)
> > [  418.346125] requeue_io 308: inode 8 size 85 at 08:11(sdb1)
> 
> Since 2.6.23-mm1 I also experience strange hangs during heavy writeouts.
> Each time I noticed this I was using emerge (package util from the
> gentoo distribution) to install/upgrade a package. The last step,
> where this hang occurred, is moving the prepared files from a tmpfs
> partion to the main xfs filesystem.
> The hangs where not fatal, after a few second everything resumed
> normal, so I was not able to capture a good image of what was
> happening.

Thank you for the detailed report.

How severe was the hangs? Only writeouts stalled, all apps stalled, or
cannot type and run new commands?

> Today it happend again, but a little more obvious. During the moving
> process the writeout stalled completly for several minutes until I hit
> SysRq+W.
> 
> /proc/meminfo:
> MemTotal:      4061808 kB
> MemFree:        881332 kB
> Buffers:             0 kB
> Cached:        2566628 kB
> SwapCached:         64 kB
> Active:         926612 kB
> Inactive:      1959136 kB
> SwapTotal:     9775416 kB
> SwapFree:      9775296 kB
> Dirty:           44948 kB
> Writeback:           0 kB
> AnonPages:      319068 kB
> Mapped:          52844 kB
> Slab:           235572 kB
> SReclaimable:   164408 kB
> SUnreclaim:      71164 kB
> PageTables:       9576 kB
> NFS_Unstable:        0 kB
> Bounce:              0 kB
> CommitLimit:  11806320 kB
> Committed_AS:   544520 kB
> VmallocTotal: 34359738367 kB
> VmallocUsed:     35004 kB
> VmallocChunk: 34359702447 kB
> HugePages_Total:     0
> HugePages_Free:      0
> HugePages_Rsvd:      0
> HugePages_Surp:      0
> Hugepagesize:     2048 kB
> 
> The 'Dirty' count did not decrease during this time and 'Writeback' stayed at 0.
> I also have /proc/pagetypeinfo ,but I see nothing interessing in
> there. (But will send it, if needed)
> 
> The output from SysRq+W:
> SysRq : Show Blocked State
>   task                        PC stack   pid father
> pdflush       D ffff81001fcc2a88     0   285      2
>  ffff810005d55580 0000000000000046 0000000000000800 0000007000000001
>  0000000000000400 ffffffff8022d61c ffffffff80817b00 ffffffff80817b00
>  ffffffff80813f40 ffffffff80817b00 ffff810100893b18 0000000000000000
> Call Trace:
>  [<ffffffff8022d61c>] task_rq_lock+0x4c/0x90
>  [<ffffffff8022c8ea>] __wake_up_common+0x5a/0x90
>  [<ffffffff805b14c7>] __down+0xa7/0x11e
>  [<ffffffff8022da70>] default_wake_function+0x0/0x10
>  [<ffffffff805b1145>] __down_failed+0x35/0x3a
>  [<ffffffff803750be>] xfs_buf_lock+0x3e/0x40
>  [<ffffffff803771fe>] _xfs_buf_find+0x13e/0x240
>  [<ffffffff8037736f>] xfs_buf_get_flags+0x6f/0x190
>  [<ffffffff803774a2>] xfs_buf_read_flags+0x12/0xa0
>  [<ffffffff80368614>] xfs_trans_read_buf+0x64/0x340
>  [<ffffffff80352151>] xfs_itobp+0x81/0x1e0
>  [<ffffffff803759de>] xfs_buf_rele+0x2e/0xd0
>  [<ffffffff80354afe>] xfs_iflush+0xfe/0x520
>  [<ffffffff803ae3b2>] __down_read_trylock+0x42/0x60
>  [<ffffffff80355a72>] xfs_inode_item_push+0x12/0x20
>  [<ffffffff80368037>] xfs_trans_push_ail+0x267/0x2b0
>  [<ffffffff8035a33b>] xlog_ticket_get+0xfb/0x140
>  [<ffffffff8035c5ae>] xfs_log_reserve+0xee/0x120
>  [<ffffffff803669e8>] xfs_trans_reserve+0xa8/0x210
>  [<ffffffff8035703a>] xfs_iomap_write_allocate+0xfa/0x410
>  [<ffffffff804ce67a>] __split_bio+0x38a/0x3c0
>  [<ffffffff80373657>] xfs_start_page_writeback+0x27/0x60
>  [<ffffffff8035660c>] xfs_iomap+0x26c/0x310
>  [<ffffffff803735d8>] xfs_map_blocks+0x38/0x90
>  [<ffffffff80374a88>] xfs_page_state_convert+0x2b8/0x630
>  [<ffffffff80374f5f>] xfs_vm_writepage+0x6f/0x120
>  [<ffffffff8026acda>] __writepage+0xa/0x30
>  [<ffffffff8026b2ce>] write_cache_pages+0x23e/0x330
>  [<ffffffff8026acd0>] __writepage+0x0/0x30
>  [<ffffffff80354db7>] xfs_iflush+0x3b7/0x520
>  [<ffffffff80375782>] _xfs_buf_ioapply+0x222/0x320
>  [<ffffffff803ae451>] __up_read+0x21/0xb0
>  [<ffffffff8034f22c>] xfs_iunlock+0x5c/0xc0
>  [<ffffffff8026b410>] do_writepages+0x20/0x40
>  [<ffffffff802b36a0>] __writeback_single_inode+0xb0/0x380
>  [<ffffffff804d052e>] dm_table_any_congested+0x2e/0x80
>  [<ffffffff802b3d8d>] generic_sync_sb_inodes+0x20d/0x330
>  [<ffffffff802b4322>] writeback_inodes+0xa2/0xe0
>  [<ffffffff8026bde6>] wb_kupdate+0xa6/0x120
>  [<ffffffff8026c2a0>] pdflush+0x0/0x1e0
>  [<ffffffff8026c3b0>] pdflush+0x110/0x1e0
>  [<ffffffff8026bd40>] wb_kupdate+0x0/0x120
>  [<ffffffff8024a32b>] kthread+0x4b/0x80
>  [<ffffffff8020c9d8>] child_rip+0xa/0x12
>  [<ffffffff8024a2e0>] kthread+0x0/0x80
>  [<ffffffff8020c9ce>] child_rip+0x0/0x12
> 
> emerge        D ffff81001fcc2a88     0  3221   8163
>  ffff81008c0679f8 0000000000000086 ffff81008c067988 ffffffff8024a719
>  ffff8100060fb008 ffffffff8022c8ea ffffffff80817b00 ffffffff80817b00
>  ffffffff80813f40 ffffffff80817b00 ffff810100893b18 0000000000000000
> Call Trace:
>  [<ffffffff8024a719>] autoremove_wake_function+0x9/0x30
>  [<ffffffff8022c8ea>] __wake_up_common+0x5a/0x90
>  [<ffffffff8022c8ea>] __wake_up_common+0x5a/0x90
>  [<ffffffff805b14c7>] __down+0xa7/0x11e
>  [<ffffffff8022da70>] default_wake_function+0x0/0x10
>  [<ffffffff805b1145>] __down_failed+0x35/0x3a
>  [<ffffffff803750be>] xfs_buf_lock+0x3e/0x40
>  [<ffffffff803771fe>] _xfs_buf_find+0x13e/0x240
>  [<ffffffff8037736f>] xfs_buf_get_flags+0x6f/0x190
>  [<ffffffff803774a2>] xfs_buf_read_flags+0x12/0xa0
>  [<ffffffff80368614>] xfs_trans_read_buf+0x64/0x340
>  [<ffffffff80352151>] xfs_itobp+0x81/0x1e0
>  [<ffffffff803759de>] xfs_buf_rele+0x2e/0xd0
>  [<ffffffff80354afe>] xfs_iflush+0xfe/0x520
>  [<ffffffff803ae3b2>] __down_read_trylock+0x42/0x60
>  [<ffffffff80355a72>] xfs_inode_item_push+0x12/0x20
>  [<ffffffff80368037>] xfs_trans_push_ail+0x267/0x2b0
>  [<ffffffff8035c532>] xfs_log_reserve+0x72/0x120
>  [<ffffffff803669e8>] xfs_trans_reserve+0xa8/0x210
>  [<ffffffff80372fe2>] kmem_zone_zalloc+0x32/0x50
>  [<ffffffff8035242b>] xfs_itruncate_finish+0xfb/0x310
>  [<ffffffff8036d8db>] xfs_free_eofblocks+0x23b/0x280
>  [<ffffffff80371d83>] xfs_release+0x153/0x200
>  [<ffffffff80377e00>] xfs_file_release+0x10/0x20
>  [<ffffffff80294041>] __fput+0xb1/0x220
>  [<ffffffff80290e94>] filp_close+0x54/0x90
>  [<ffffffff802927af>] sys_close+0x9f/0x100
>  [<ffffffff8020bbbe>] system_call+0x7e/0x83
> 
> 
> After this SysRq+W writeback resumed again. Possible that writing
> above into the syslog triggered that.

Maybe. Are the log files on another disk/partition?

> The source tmpfs is mounted with any special parameters, but the
> target xfs filesystem resides on a dm-crypt device that is on top a 3
> disk RAID5 md.
> During the hang all CPUs where idle.

No iowaits? ;-)

> The system is x86_64 with CONFIG_NO_HZ=y, but was still receiving ~330
> interrupts per second because of the bttv driver. (But I was not using
> that device at this time.)
> 
> I'm willing to test patches or more provide more information, but lack
> a good testcase to trigger this on demand.

Thank you. Maybe we can start by the applied debug patch :-)

Fengguang

[-- Attachment #2: writeback-debug.patch --]
[-- Type: text/x-diff, Size: 1926 bytes --]

---
 mm/page-writeback.c |   23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

--- linux-2.6.23-rc8-mm2.orig/mm/page-writeback.c
+++ linux-2.6.23-rc8-mm2/mm/page-writeback.c
@@ -98,6 +98,26 @@ EXPORT_SYMBOL(laptop_mode);
 
 /* End of sysctl-exported parameters */
 
+#define writeback_debug_report(n, wbc) do {                               \
+	__writeback_debug_report(n, wbc, __FILE__, __LINE__, __FUNCTION__); \
+} while (0)
+
+void __writeback_debug_report(long n, struct writeback_control *wbc,
+		const char *file, int line, const char *func)
+{
+	printk("%s %d %s: %s(%d) %ld "
+			"global %lu %lu %lu "
+			"wc %c%c tw %ld sk %ld\n",
+			file, line, func,
+			current->comm, current->pid, n,
+			global_page_state(NR_FILE_DIRTY),
+			global_page_state(NR_WRITEBACK),
+			global_page_state(NR_UNSTABLE_NFS),
+			wbc->encountered_congestion ? 'C':'_',
+			wbc->more_io ? 'M':'_',
+			wbc->nr_to_write,
+			wbc->pages_skipped);
+}
 
 static void background_writeout(unsigned long _min_pages);
 
@@ -404,6 +424,7 @@ static void balance_dirty_pages(struct a
 			pages_written += write_chunk - wbc.nr_to_write;
 			get_dirty_limits(&background_thresh, &dirty_thresh,
 				       &bdi_thresh, bdi);
+			writeback_debug_report(pages_written, &wbc);
 		}
 
 		/*
@@ -568,6 +589,7 @@ static void background_writeout(unsigned
 		wbc.pages_skipped = 0;
 		writeback_inodes(&wbc);
 		min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+		writeback_debug_report(min_pages, &wbc);
 		if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
 			/* Wrote less than expected */
 			if (wbc.encountered_congestion)
@@ -643,6 +665,7 @@ static void wb_kupdate(unsigned long arg
 		wbc.encountered_congestion = 0;
 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 		writeback_inodes(&wbc);
+		writeback_debug_report(nr_to_write, &wbc);
 		if (wbc.nr_to_write > 0) {
 			if (wbc.encountered_congestion)
 				congestion_wait(WRITE, HZ/10);