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

From: Fengguang Wu
Date: Thu Nov 01 2007 - 03:57:54 EST

On Wed, Oct 31, 2007 at 04:22:10PM +0100, Torsten Kaiser wrote:
> On 10/22/07, Fengguang Wu <wfg@xxxxxxxxxxxxxxxx> 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
---
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);