Determining the size of a process

Each process has a per-process region (pregion) table associated with it that points to the regions that are private to it or that it shares with other processes. ``The relationship between a process' pregion table and the system region table'' shows how a process's pregion entry points into the system region table. This entry in the region table may be shared with other processes if it refers to program text (executable code).

The relationship between a process' pregion table and the system region table

To determine the current memory utilization of a process, you must add together the number of pages of physical memory that are described by the process' regions. If the size of several processes is being determined, you need to take care not to count shared regions more than once.

Use the proc and region commands of crash(ADM) to determine the size of a process as follows:

1. Issue the proc command to find the process table slot number for the program in which you are interested. This yields output similar to the following:

   SLOT ST PID   PPID  PGRP UID PRI CPU EVENT        NAME         FLAGS
     11 s    17    12    12   0  33   0 proc+0x968   smallapp     load nxec
   

   The number in the first column (SLOT) is the process table slot number. The process ID is shown under the column PID. In this example, the program smallapp has process ID 17 and occupies slot 11 in the process table.

2. Run the pregion command to determine the regions associated with the process being studied. For example, enter pregion 11 for slot number 11. The output has the following form:

      PREG REG#      REGVA  TYPE FLAGS
         0   12          0  text rdonly
         1   20   0x400000  data
         2   21 0x7ffffffc stack
   

   The REG# column of this output shows the region table entries associated with this process; REGVA shows the virtual address of this region. TYPE identifies whether this region is text, data, stack, library text, library data, and so on; FLAGS identifies the characteristics of the region (read-access, write access, and so on).

3. Issue the reg command with the region table number(s) of the process. For example:

   > reg 12 20 21
    
   SLOT  PGSZ VALID  SMEM NONE SOFF  REF SWP NSW FORW BACK INOX TYPE FLAGS
     12     1     1     1    0    0   13   0   0   14    8   35 stxt done
     20     1     1     1    0    0    1   0   0  267   21   35 priv done
     21     2     1     1    0    0    1   0   0  267   22      priv stack
   

   The PGSZ column represents the maximum size of the region in pages. The VALID column indicates the number of 4KB pages that are currently in RAM. The TYPE column shows whether this is a private region (priv) or a shared text region (stxt).

   Summing the #VL sizes of all regions for the process shows the number of pages of memory being used by a program if it is only invoked once on the system. In this case, the sum is 3 pages. If multiple invocations of a program are run on a system, you can sum the #VL sizes for their shared text and private regions separately; the same amount of memory will be dedicated to shared text regions regardless of how many invocations of that program are running. The sum of the #VL sizes for private regions is the amount of extra memory that will be consumed by each subsequent invocation of this program.

Finding regions shared by processes

You can use the rtop command of crash to find which regions are shared by processes. For example to determine which processes share regions 0 through 4, issue the command rtop 0..4.

Finding the largest processes on a system

Use the region and rtop commands of crash to identify the largest processes on the system.

1. To list the slot numbers of the five largest regions, enter:

   > reg | sort +1rn | head -5 | awk '{print $1}'
   12
   5
   8
   0
   1
   

   The example output from this command shows the five largest regions in decreasing order of size.

2. Run rtop for the regions listed in the previous step to see which processes are associated with these regions. For the example above, you would enter:

   > rtop 12 5 8 0 1
   

   The output from this command will show the process table entries associated with each of the specified regions.