mmap failed messages in syslog

[Shawn Heisey]

I'm getting mmap failed messages in syslog on version 1.2.15 for 
dovecot.index.cache files.  This old dovecot version is installed with 
debian packages.  The OS and all software is 64-bit.

I've found info on this log message, with a suggested fix of raising 
vsz_limit ... but this seems to be a config option for dovecot 2.x, not 1.x.

The file it complains about being unable to mmap is only 90MB, and the 
biggest cache file I have found on the system is only 180MB. The system 
has 4GB of total memory with about 1GB of that allocated to OS disk 
cache right now.  The mmap functionality provided by the OS doesn't use 
*actual* memory, so the amount of memory I have should be irrelevant.

Checking 'ulimit -a' with several users shows that vmemory is unlimited 
for all of them.

How do I go about allowing docevot 1.x to use more virtual memory?  I do 
have a migration planned to Ubuntu 16, where I can run a 2.x version, 
but that's not going to happen for a while.

Thanks,
Shawn