Sudden "hangs"....

Rogier Wolff
2010-09-16T14:33:09Z

Hi,

It seems my home workstation hangs on a "mkdir" once every morning for
about half a minute. It'll freeze whatever I'm doing and continue
happily 30 seconds later, but I can't figure out what's going on
because it's frozen...

My server did it just now and I was able to grab some more
debugging info.....

obelix:~> time mkdir /recover3/testdir
0.000u 0.004s 2:11.83 0.0% 0+0k 0+0io 5pf+0w
obelix:~>

Over two minutes to make a directory! (I have the impression that
the wait is for something to finish, so if I had started the mkdir
a minute earlier, it would've taken a minute longer).

The process:
28649 root 20 0 0 0 0 D 6.3 0.0 0:11.69 flush-9:0

was in "top", and as shown here in "disk wait" mode.

While this is going on, "vmstat 1" shows:

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 1 5368 12764 324804 1616932 0 0 464 0 244 477 0 2 0 98
0 1 5368 12764 324556 1617168 0 0 448 0 255 474 0 1 0 99
0 1 5368 12764 324952 1616832 0 0 472 0 257 487 0 1 0 99

... about 400 kbytes of IO per second. This is similar to the
single-disk machine at home.

The server runs:

Linux version 2.6.34 (wolff@abra2) (gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)) #5 SMP Tue Jun 1 14:44:01 CEST 2010

at home I run:
Linux version 2.6.28-19-generic (buildd@palmer) (gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4) ) #61-Ubuntu SMP Wed May 26 23:35:15 UTC 2010

Does anybody know what's going on?

Roger.

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