Re: long hangs when deleting large directories (3.0-rc3)

Dave Chinner
2011-06-29T07:24:51Z

On Wed, Jun 29, 2011 at 08:19:54AM +0200, Markus Trippelsdorf wrote:
> On 2011.06.29 at 14:31 +1000, Dave Chinner wrote:
> > On Wed, Jun 22, 2011 at 05:30:47PM +1000, Dave Chinner wrote:
> > > Jun 22 08:53:09 x4 kernel: XFS (sdb1): ail: ooo splice, tail 0x12000156e7, item 0x12000156e6
> > > Jun 22 08:53:09 x4 kernel: XFS (sdb1): ail: ooo splice, walked 15503 items
> > > .....
> > > Jun 22 08:53:12 x4 kernel: XFS (sdb1): ail: ooo splice, tail 0x12000156e7, item 0x12000156e6
> > > Jun 22 08:53:12 x4 kernel: XFS (sdb1): ail: ooo splice, walked 16945 items
> > >
> > > Interesting is the LSN of the tail - it's only one sector further on
> > > than the items being inserted. That's what I'd expect from a commit
> > > record write race between two checkpoints. I'll have a deeper look
> > > into whether this can be avoided later tonight and also whether I
> > > can easily implement a "last insert cursor" easily so subsequent
> > > inserts at the same LSN avoid the walk....
> >
> > Ok, so here's a patch that does just this. I should probably also do
> > a little bit of cleanup on the cursor code as well, but this avoids
> > the repeated walks of the AIL to find the insert position.
> >
> > Can you try it without the WQ changes you made, Marcus, and see if
> > the interactivity problems go away?
>
> Sorry to be the bringer of bad news, but this made things much worse:
>
> -------cpu0-usage--------------cpu1-usage--------------cpu2-usage--------------cpu3-usage------ --dsk/sdc-- ---system-- ---load-avg--- --dsk/sdc--
> usr sys idl wai hiq siq:usr sys idl wai hiq siq:usr sys idl wai hiq siq:usr sys idl wai hiq siq| read writ| int csw | 1m 5m 15m |reads writs
> 1 1 98 0 0 0: 0 1 99 0 0 0: 0 1 99 0 0 0: 0 1 99 0 0 0| 0 0 | 603 380 |0.66 0.55 0.28| 0 0
> 1 0 99 0 0 0: 1 0 99 0 0 0: 1 19 80 0 0 0: 0 0 100 0 0 0| 0 0 | 719 383 |0.66 0.55 0.28| 0 0
> 3 1 96 0 0 0: 3 1 96 0 0 0: 1 52 47 0 0 0: 0 0 100 0 0 0| 0 6464k|1847 919 |0.66 0.55 0.28| 0 202
> 2 13 85 0 0 0: 2 2 96 0 0 0: 1 56 43 0 0 0: 1 31 69 0 0 0|4096B 256k|1910 1280 |0.68 0.56 0.28| 1 8
> > 0 1 99 0 0 0: 0 0 100 0 0 0: 0 1 99 0 0 0: 0 100 0 0 0 0| 0 0 |1256 170 |0.68 0.56 0.28| 0 0
> > 0 1 99 0 0 0: 1 1 98 0 0 0: 1 0 99 0 0 0: 0 99 0 0 0 1| 0 0 |1395 229 |0.68 0.56 0.28| 0 0
> > 0 0 100 0 0 0: 0 0 100 0 0 0: 0 3 97 0 0 0: 0 100 0 0 0 0| 0 512B|1304 167 |0.68 0.56 0.28| 0 1
> > 1 1 98 0 0 0: 1 1 98 0 0 0: 0 0 100 0 0 0: 0 99 0 0 0 1| 0 0 |1211 146 |0.68 0.56 0.28| 0 0
> > 0 0 100 0 0 0: 0 0 100 0 0 0: 0 1 99 0 0 0: 0 97 0 0 0 3| 0 0 |1270 149 |0.87 0.60 0.30| 0 0
> 5 2 65 29 0 0: 2 3 95 0 0 0: 1 0 99 0 0 0: 2 24 72 0 0 1| 0 8866k|2654 2398 |0.87 0.60 0.30| 0 496
> 6 2 25 67 0 0: 3 1 59 37 0 0: 0 0 100 0 0 0: 4 4 92 0 0 0| 0 4554k|2224 2494 |0.87 0.60 0.30| 0 399
> 1 1 98 0 0 0: 0 0 83 17 0 0: 1 3 96 0 0 0: 0 1 99 0 0 0| 0 2270k|1079 1030 |0.87 0.60 0.30| 0 200
> 1 1 98 0 0 0: 1 1 98 0 0 0: 0 1 99 0 0 0: 1 0 99 0 0 0| 0 9216B| 713 567 |0.87 0.60 0.30| 0 2
> 0 0 100 0 0 0: 1 1 98 0 0 0: 0 0 100 0 0 0: 0 1 99 0 0 0| 0 0 | 492 386 |0.80 0.59 0.30| 0 0
>
> As you can see in the table above (resolution 1sec) the hang is now
> 5-6 seconds long, instead of the 1-3 seconds seen before.

Interesting. I checked that the ordering was correct in each case
adn that it was behaving correctly here.

Can you add the following patch and send me the dmesg output over a
hang? It will tell me where the cursor is being initialised and when
it is being dropped, so should indicate if a specific insert chain
is getting stuck or doing something stoopid.

Cheers,

Dave
--
Dave Chinner
david@fromorbit.com

---
fs/xfs/xfs_trans_ail.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 272e7fa..a087cbb 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -234,6 +234,8 @@ xfs_trans_ail_cursor_done(
struct xfs_ail_cursor *prev = NULL;
struct xfs_ail_cursor *cur;

+ printk(KERN_WARNING "done cur %p, lip %p/0x%llx\n",
+ done, done->item, done->item ? done->item->li_lsn : 0);
done->item = NULL;
if (done == &ailp->xa_cursors)
return;
@@ -323,6 +325,8 @@ __xfs_trans_ail_cursor_last(
break;
}
out:
+ printk(KERN_WARNING "last cur %p, init %d lsn 0x%llx, lip %p/0x%llx\n",
+ cur, do_init, lsn, lip, lip ? lip->li_lsn : 0);
if (cur)
cur->item = lip;
return lip;