question about ps (AIX 1.1 PS/2)

[Jack F. Vogel]

In article <237 at bally.Bally.COM> pete at bally.Bally.COM (Pete Gregory) writes:
>
>Sometimes, when I do a ps -el (that's /bin/ps), I get the following
>two errors (and no ps output):
>
>	swapread: dbd not of type DBD_SWAP
>	getupages: Can't read upage from swap for proc nnnn
>
>Any ideas?
 
What is happening here is nothing peculiar to AIX, it can happen on other
Unix variants as well as far as I know. It is likely to occur most often
under heavy system activity. I believe the scenario goes something like
this.... You fire up the ps command, it reads the process table and finds
that the user structure that it wants to read is swapped out. So it calls
swapread to get at it. Perhaps it sleeps on this I/O or is preempted for
whatever reason. Then during the time that it is not running, that process
that was swapped out it brought into core. Now when ps is again scheduled
the swapread fails because that page is no longer on the paging device.
As I said, I believe you should only see this with heavy system activity.
Also subsequent invocations of ps, due to the dynamic nature of things,
should read things successfully.

Hope this sheds some light.

Disclaimer: These opinions are mine, not necessarily LCC's

-- 
Jack F. Vogel			jackv at seas.ucla.edu
AIX Technical Support	              - or -
Locus Computing Corp.		jackv at ifs.umich.edu