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From: Wolfgang Zenker <wolfgang@lyxys.ka.sub.org>
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Subject: swap_pager forgetting device?
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Hello,

I have a strange effect on a heavily used webserver (Apache 1.3 & PHP5)
running 5.4-RELEASE-p11.
This machine did use a lot of its 16 GB of swap last Friday, but recovered
since then with now 46 MB of swap being used:

# swapinfo
Device          1K-blocks     Used    Avail Capacity
/dev/da0s1b      16777216    46652 16730564     0%

Now I see messages like these in syslog:

Feb 20 12:20:03 www1 kernel: swap_pager: indefinite wait buffer: device: [NULL], blkno: 94333, size: 8192
Feb 20 12:20:03 www1 kernel: swap_pager: indefinite wait buffer: device: [NULL], blkno: 42814, size: 32768

I guess they are related to these processes:
# ps axuw | grep 'D.*httpd'
www     4130  0.0  0.5 36996 19248  ??  DL   Fri07PM   0:13.02 /usr/local/sbin/httpd -DSSL
www     4140  0.0  0.0  7944     8  ??  DE   Fri07PM   0:06.86 /usr/local/sbin/httpd -DSSL
www     4182  0.0  0.3 35696  9220  ??  DL   Fri07PM   0:07.85 /usr/local/sbin/httpd -DSSL
www     4184  0.0  0.2 35808  8424  ??  DL   Fri07PM   0:09.89 /usr/local/sbin/httpd -DSSL

Looks to me like the swap_pager swapped out blocks used by these processes
and somehow managed to "forget" the device.

Anyone seen this before?

Wolfgang