Re: Child process limits cumulative or instantaneous?
Re: Child process limits cumulative or instantaneous?
- Subject: Re: Child process limits cumulative or instantaneous?
- From: Ralph Castain <email@hidden>
- Date: Fri, 27 Feb 2009 09:43:20 -0700
I appreciate that info. There is plenty of swap space available. We
are not exceeding the total number of processes under execution at any
time, nor the total number of processes under execution by a single
user - assuming that these values are interpreted as instantaneous and
not cumulative.
In other words, if you look at any given time, you will see that the
total number of processes is well under the system limit, and the
number of processes under execution by the user is only 4, which is
well under the system limit.
However, the total number of processes executed by the user
(cumulative over the entire time the job has been executing) is over
263 and thus pushing the system limit IF that limit is cumulative and
not instantaneous.
Hope that helps clarify the situation
Ralph
On Feb 27, 2009, at 9:37 AM, mm w wrote:
ERRORS
Fork() will fail and no child process will be created if:
[EAGAIN] The system-imposed limit on the total number
of pro-
cesses under execution would be exceeded.
This limit
is configuration-dependent.
[EAGAIN] The system-imposed limit MAXUPRC (<sys/
param.h>) on
the total number of processes under execution
by a
single user would be exceeded.
[ENOMEM] There is insufficient swap space for the new
process.
On Fri, Feb 27, 2009 at 8:13 AM, Ralph Castain <email@hidden> wrote:
Hello folks
I'm the run-time developer for Open MPI and am encountering a
resource
starvation problem that I don't understand. What we have is a test
program
that spawns a child process, exchanges a single message with it,
and then
the child terminates. We then spawn another child process and go
through the
same procedure.
This paradigm is typical of some of our users who want to build
client-server applications using MPI. In these cases, they want the
job to
run essentially continuously, but have a rate limiter in their
application
so only one client is alive at any time.
We have verified that the child processes are properly terminating.
We have
monitored and observed that all file descriptors/pipes are being
fully
recovered after each cycle.
However, after 263 cycles, the fork command returns an error
indicating that
we have exceeded the number of allowed child processes for a given
process.
This is fully repeatable, yet the number of child processes in
existence at
any time is 1, as verified by ps.
Do you have any suggestions as to what could be causing this
problem? Is the
limit on child processes a cumulative one, or instantaneous?
Appreciate any help you can give
Ralph
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-mmw
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