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Full Discussion: Linux Virtual Memory Question
Top Forums UNIX for Advanced & Expert Users Linux Virtual Memory Question Post 302560486 by Corona688 on Friday 30th of September 2011 01:44:58 AM
Old 09-30-2011
Quote:
Originally Posted by jlliagre
You might be confusing with allocated memory.
Virtual memory as reported by top is the sum of memory present either on disk (mostly SWAP) or on RAM (RES).
I beg to differ:

Code:
$ cat megaalloc.c
#include <stdio.h>
#include <unistd.h>

int main(void)
{
	sbrk((1024L*1024L*1024L));
	while(1);
}
$ gcc megaalloc.c
$ ./a.out

Code:
top - 17:46:55 up  6:12,  4 users,  load average: 0.24, 0.17, 0.11
Tasks: 127 total,   2 running, 124 sleeping,   0 stopped,   1 zombie
Cpu(s): 45.5%us,  3.5%sy,  0.0%ni, 48.2%id,  0.3%wa,  2.5%hi,  0.0%si,  0.0%st
Mem:   3797432k total,  3236628k used,   560804k free,   161272k buffers
Swap:  2104476k total,        0k used,  2104476k free,  1373932k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND            
10599 monttyle  20   0 1027m  296  228 R   73  0.0   0:02.19 a.out              
 3825 root      20   0  748m  82m  10m S    8  2.2  25:52.57 X                  
10017 monttyle  20   0  149m 8032 5936 S    8  0.2   3:49.15 mplayer            
 9712 monttyle  20   0  220m  15m  10m S    5  0.4   4:38.51 gnome-terminal     
 5988 monttyle  20   0 1591m 1.3g  26m S    3 37.0  52:49.71 firefox-bin        
 9710 monttyle  20   0 71692  13m 4900 S    2  0.4   3:03.59 wish               
 5256 monttyle  20   0  216m  14m  10m S    1  0.4   2:54.01 metacity           
    8 root      20   0     0    0    0 S    0  0.0   0:10.05 events/1           
  453 root      20   0     0    0    0 S    0  0.0   1:20.78 kondemand/1        
 5278 monttyle  20   0  346m  23m  15m S    0  0.6   4:30.59 gnome-panel        
    1 root      20   0  3892  620  516 S    0  0.0   0:01.42 init               
    2 root      20   0     0    0    0 S    0  0.0   0:00.00 kthreadd           
    3 root      RT   0     0    0    0 S    0  0.0   0:00.06 migration/0        
    4 root      20   0     0    0    0 S    0  0.0   0:00.42 ksoftirqd/0        
    5 root      RT   0     0    0    0 S    0  0.0   0:00.01 migration/1        
    6 root      20   0     0    0    0 S    0  0.0   0:02.82 ksoftirqd/1        
    7 root      20   0     0    0    0 S    0  0.0   0:07.20 events/0

My process certainly does not have 1027M resident. It doesn't have it on disk, either -- having not used any of that gig of ram, none of it is actually paged in, resident, or even backed in any form. Other systems might demand sufficient swap to back it but not Linux, which by default has virtual swap.

On a 64-bit system you can also inflate that value by plunking in your entire hard disk as a memory segment via mmap. 300G virtual. I suppose that would count as on disk though.
Last edited by Corona688; 09-30-2011 at 02:50 AM..
 

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LEARN ABOUT OSF1

volunroot

volunroot(8)						      System Manager's Manual						      volunroot(8)

NAME

       volunroot - Remove Logical Storage Manager hooks for rootable volumes

SYNOPSIS

       /usr/sbin/volunroot [-a	| -A]

OPTIONS

       Specifies  that	all  volumes on the system disk be converted back to UNIX disk partitions, not just the root and swap volumes, rootvol and
       swapvol.  Forces removal of the private region unless it is the last one in the system.

DESCRIPTION

       The volunroot script can be used to restore the accessibility of the root, swap, and other file systems on the boot disk  directly  through
       disk  partitions  instead  of  through volume devices. The script also removes other changes that were made to enable booting of the system
       from the root volume, so that the system will boot with no dependency on the Logical Storage Manager.

       When used with no options, volunroot affects only the root and swap volumes, rootvol and swapvol.

       For volunroot to work properly, only one plex must exist for each of the affected volumes. This plex must be the one created by	volrootmir
       or the original plex created when the root disk was encapsulated. This ensures that the underlying subdisks will have equivalent partitions
       defined for them on the disk.

       If these conditions are not met, the volunroot operation fails and none of the volumes are converted to disk partitions.

       The unwanted plexes can be removed using either voledit or volplex.

SEE ALSO

       volencap(8), voldiskadm(8), voledit(8), volintro(8), volplex(8), volrootmir(8)

																      volunroot(8)
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