long hangs when deleting large directories (3.0-rc3)

[Markus Trippelsdorf]

On 2011.06.29 at 17:24 +1000, Dave Chinner wrote:
> 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.

The kernel log is attached.
rm -fr && sync starts at Jun 29 09:32:24.

-- 
Markus
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