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Top Forums UNIX for Dummies Questions & Answers Interpretting the result of TOP command Post 7249 by Perderabo on Friday 21st of September 2001 03:58:30 PM
Old 09-21-2001
If you and I are on the system and we both run vi to edit different files, no modern kernel will give us two complete seperate copies of vi. The program's memory will be broken into segments. The text segment contains (roughly) the code and the unchanging constants. We will share one text segment bewteen us. We each get a data segment and we each get a stack. top will report the total of all the segments for each process, but you can't add them up and expect that system needs to use that much physical memory. With shared libraries, it get a bit more confused. If you use emacs and I use vi, will we have different text segments, but we both might be using the same copy of printf and other library functions. Oracle is probably using shared memory which further complicates things. Shared memory is another memory segment, and again many processes can map that seqment into their memory space. So 100 copies of a 700 MB program might easily fit in a couple of GB of memory.

In view of all this, it really isn't possible anymore to truly say how much memory a single process is using in the sense that you want. Each process really is using 700MB, but they are sharing very large chucks of this with other processes.

Most versions of top have a line that shows system-wide memory usage.
 

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plock(2)							System Calls Manual							  plock(2)

Name
       plock - lock or unlock process, text, or data in memory

Syntax
       #include <sys/lock.h>

       int plock (op)
       int op;

Description
       The  call allows the calling process to lock its text segment (text lock), its data segment (data lock), or both its text and data segments
       (process lock) into memory.  Locked segments are immune to page outs, and the process is immune to swap outs.  The call also unlocks  these
       segments.

       The op argument specifies the following:

       PROCLOCK  Lock text and data segments into memory (process lock)

       TXTLOCK	 Lock text segment into memory (text lock)

       DATLOCK	 Lock data segment into memory (data lock)

       UNLOCK	 Remove locks

Return Values
       Upon  successful  completion,  a  value of 0 is returned to the calling process.  Otherwise, a value of -1 is returned, and errno is set to
       indicate the error.

Diagnostics
       The call fails under the following conditions:

       [EPERM]	      The effective user ID of the calling process is not superuser.

       [EINVAL]       The op argument is equal to PROCLOCK, and a process lock, a text lock, or a data lock already exists on the calling process.

       [EINVAL]       The op argument is equal to TXTLOCK, and a text lock or a process lock already exists on the calling process.

       [EINVAL]       The op argument is equal to DATLOCK, and a data lock or a process lock already exists on the calling process.

       [EINVAL]       The op argument is equal to UNLOCK, and no type of lock exists on the calling process.

Restrictions
       The effective user ID of the calling process must be superuser to use this call.

       Both PROCLOCK and TXTLOCK lock the text segment of a process, and a locked text segment is locked for all sharing processes.

       Because the effective user ID of the calling process is superuser, take care not to lock more virtual pages than can be contained in physi-
       cal memory.  A deadlock can result.

See Also
       execve(2), exit(2), fork(2), shmctl(2)

																	  plock(2)
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