Andreas Dilger writes:
> Olaf Weber writes:
> > In a similar vein, if a process dies due to SIGXCPU or SIGXFSZ that
> > you know it dies because it ran into a cpu or file limit. Yes, I
> > would like to have some OS support from an overcommitting OS, so that
> > if it decides to kill a process of mine because it ran out memory I
> > get SIGXMEM instead of SIGBUS.
>
> If you look at the AIX documentation, they have a signal like this. The
> following is quoted from the following URL, and I urge people posting to
> this OOM thread to read this document to get a better understanding of
> what a system with (optional) no-overcommit behaves like.
>
> http://www.rs6000.ibm.com/doc_link/en_US/a_doc_lib/aixbman/admnconc/pag_space_under.htm
>
> "The system monitors the number of free paging space blocks and
> detects when a paging-space shortage exists. When the number of free
> paging-space blocks falls below a threshold known as the paging-space
> warning level, the system informs all processes (except kprocs)
> of this condition by sending the SIGDANGER signal. If the shortage
> continues and falls below a second threshold known as the paging-space
> kill level, the system sends the SIGKILL signal to processes that are
> the major users of paging space and that do not have a signal handler
> for the SIGDANGER signal (the default action for the SIGDANGER signal
> is to ignore the signal). The system continues sending SIGKILL signals
> until the number of free paging-space blocks is above the paging-space
> kill level."
>
> Those advocates of "no OOM possible" implementations should read the part:
>
> "The AIXwindows server currently requires more than 250MB of paging space
> when the application runs in early allocation mode."
>
> It is interesting to note that memory overcommit has recently been ADDED
> to AIX, arguably one of the most popular MISSION CRITICAL BUSINESS Unixes.
??? I recall seeing SIGDANGER and SIGKILL on low memory back in 1991
when we using some AIX machines. I wouldn't call that recent.
Regards,
Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca
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