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From: Dan Bonachea <dobonachea AT lbl DOT gov>
Date: Thu, 30 Mar 2017 15:51:34 -0400
Message-ID: <CAJTO8-ZYz-v9YVWsv5JS4DUXhapHfgNOzUxAnHw7C_7eS17hJg@mail.gmail.com>
Subject: How to ulimit virtual memory on Cygwin-64 processes?
To: cygwin AT cygwin DOT com
Content-Type: text/plain; charset=UTF-8

Is there a way to get ulimit-style virtual memory limit enforcement on
64-bit Cygwin processes?

I'm a programmer and occasionally I have a bug that sends a process
into a memory-grabbing tail-spin. On 32-bit Cygwin, such a runaway
process gets stopped cold at 4GB VM (and usually crashes), but 4GB is
well short of the physical memory on my 64-bit windows system so this
doesn't affect my system stability.

However a similar runaway process on 64-bit Cygwin is easily capable
of grabbing nearly all of the memory on my system, which can lead to
Very Bad Things - ie unrelated user processes start crashing, desktop
window manager disappears, and the system slows to a crawl or freezes
entirely - making it difficult or impossible to kill the run-away.
Several times now I've had to hard power-cycle to recover from such a
Cygwin-64 runaway memory-grabbing process, and have lost some data as
a result.

You can replicate this behavior with a very simple program: (however I
DON'T recommend running this)

#include <stdlib.h>
#include <stdio.h>

int main() {
  printf("WARNING: I'm stealing all your memory, hit control-c to
cancel!!!\n");fflush(0);
  while(1) malloc(1e6);
  return 0;
}

The traditional POSIX solution to this problem is setrlimit() aka bash
ulimit, but that does not appear to be implemented in Cygwin 2.7.0:

$ ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
file size               (blocks, -f) unlimited
open files                      (-n) 256
pipe size            (512 bytes, -p) 8
stack size              (kbytes, -s) 2036
cpu time               (seconds, -t) unlimited
max user processes              (-u) 256
virtual memory          (kbytes, -v) unlimited

$ ulimit -v 1048576
bash: ulimit: virtual memory: cannot modify limit: Invalid argument

Is there any hidden setting or other way to enforce a reasonable VM /
heap memory / page commit limit on 64-bit Cygwin processes (or even
all windows processes) via some other mechanism? I'm running Windows 7
Pro.

I've searched the Cygwin mailing list archives, user guide, FAQ, and
Google and not found a suitable answer. I've tried the peflags utility
mentioned in the Cygwin user guide, but that doesn't seem capable of
doing what I need, even for a single executable (although ideally I
want to enforce a system-wide limit).

Thanks for your consideration.

-Dan Bonachea

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