Cyrus 2.4.13 memory use

[David Carter]

We are currently in the process of migrating from 2.3.14 (with lots
of local patches) to a fairly vanilla 2.4.13.

One small curiosity is that the memory use per IMAP session seems
to have increased dramatically. I'm looking at the output of the
Linux "free" command after buffer cache has been subtracted:

              total       used       free  shared  buffers   cached
Mem:       8239436    7206520    1032916       0  426276    4207948
-/+ buffers/cache:    2572296    5667140
                       ^^^^^^^

  2.3.14: 2572296 KBytes with 2909 IMAP sessions:  884 KBytes/session
  2.4.13: 3426388 KBytes with 1247 IMAP sessions: 2747 KBytes/session

This is moving from 32-bit SLES 10 to 64-bit SLES 11. I was expecting a 
modest increase as pointers and "unsigned long" double in size.

A 3.1 times increase is rather more than I was expecting. (I'm going to 
try running 32bit binaries on a 64 bit system to see if that makes a 
significant difference).

pmap and /proc/[pid]/smaps suggests that most of the increase is in the 
heap segment which is used by malloc() and the brk() system call.

It looks like 3000 IMAP sessions are going to take around 8 GBytes of RAM 
just to run, and we will need to buy additional RAM for buffer cache. This 
isn't the end of the world: memory is cheap. I'm just curious if anyone 
else saw a similar increase when upgrading from 2.3 to 2.4.

-- 
David Carter                             Email: David.Carter at ucs.cam.ac.uk
University Computing Service,            Phone: (01223) 334502
New Museums Site, Pembroke Street,       Fax:   (01223) 334679
Cambridge UK. CB2 3QH.