pmap -x and [ anon ]

From: Vincent Detzel (accrosys@wanadoo.fr)
Date: Thu Apr 24 2003 - 17:58:06 EDT


Dear gurus,

I have a process which keeps on growing it's private memory. Purify
(latest 2003 version) does not find any memory leak and I wonder whether
it is lying or not. (quite interesting feature from a computer point of
view).

After some process (thread creation/termination), the pmap -x output
differs with the following additional line :
> 7B506000 16 16 - 16 read/write/exec [ anon ]
(SunOS carbon 5.8 Generic_108528-19 sun4u sparc SUNW,Ultra-250)

Through dbx, I've noticed that this block is 95% filled with 0.

After few minutes of high activity, this process keeps on growing and at
the very end it crashes. Here are the last 2 lines of pmap after such test.
Start :
             Kbytes Resident Shared Private
total Kb 54000 27136 24688 2448

After a few minutes :
             Kbytes Resident Shared Private
total Kb 72272 29344 25112 4232

I have 2 questions :
  - Before calling pmap I expected to see an increase of the stack
    or the heap and I was quite surprised to see these mysterious
    anon blocks which does seem not belong to the stack nor the heap.
    What do they represent ?

  - What's the difference between the total Kb column and the
    resident column ? total = resident + something. What's
    this "something" exactly ?

Any tips ? Any recommended links/reading ?

Thanks in advance.

-vincent
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