Operating Systems AIX ulimits max locked memory virtual memory Post 302224017 by big123456 on Tuesday 12th of August 2008 03:46:36 AM
ulimits max locked memory virtual memory

Would any one be so kind to explain me :
are ulimits defined for each user seperately ? When ?
Specialy what is the impact of :
max locked memory
virtual memory

on performance of applications for a user.

Many thanks.

PS :
this is what I can see in MAN :
ulimit [-SHacdflmnpstuv [limit]]
              Provides control over the resources available to the shell and to processes started by it, on systems that allow such control.  The -H and -S options  spec-
              ify  that  the  hard  or soft limit is set for the given resource.  A hard limit cannot be increased once it is set; a soft limit may be increased up to the
              value of the hard limit.  If neither -H nor -S is specified, both the soft and hard limits are set.  The value of limit can be a number in the  unit  speci-
              fied  for  the resource or one of the special values hard, soft, or unlimited, which stand for the current hard limit, the current soft limit, and no limit,
              respectively.  If limit is omitted, the current value of the soft limit of the resource is printed, unless the -H option  is  given.   When  more  than  one
              resource is specified, the limit name and unit are printed before the value.

Last edited by big123456; 08-12-2008 at 05:10 AM..
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MLOCK(2)						      BSD System Calls Manual							  MLOCK(2)

mlock, munlock -- lock (unlock) physical pages in memory LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/mman.h> int mlock(const void *addr, size_t len); int munlock(const void *addr, size_t len); DESCRIPTION
The mlock() system call locks into memory the physical pages associated with the virtual address range starting at addr for len bytes. The munlock() system call unlocks pages previously locked by one or more mlock() calls. For both, the addr argument should be aligned to a mul- tiple of the page size. If the len argument is not a multiple of the page size, it will be rounded up to be so. The entire range must be allocated. After an mlock() system call, the indicated pages will cause neither a non-resident page nor address-translation fault until they are unlocked. They may still cause protection-violation faults or TLB-miss faults on architectures with software-managed TLBs. The physical pages remain in memory until all locked mappings for the pages are removed. Multiple processes may have the same physical pages locked via their own virtual address mappings. A single process may likewise have pages multiply-locked via different virtual mappings of the same pages or via nested mlock() calls on the same address range. Unlocking is performed explicitly by munlock() or implicitly by a call to munmap() which deallocates the unmapped address range. Locked mappings are not inherited by the child process after a fork(2). Since physical memory is a potentially scarce resource, processes are limited in how much they can lock down. A single process can mlock() the minimum of a system-wide ``wired pages'' limit and the per-process RLIMIT_MEMLOCK resource limit. These calls are only available to the super-user. RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error. If the call succeeds, all pages in the range become locked (unlocked); otherwise the locked status of all pages in the range remains unchanged. ERRORS
The mlock() system call will fail if: [EPERM] The caller is not the super-user. [EINVAL] The address given is not page aligned or the length is negative. [EAGAIN] Locking the indicated range would exceed either the system or per-process limit for locked memory. [ENOMEM] Some portion of the indicated address range is not allocated. There was an error faulting/mapping a page. The munlock() system call will fail if: [EPERM] The caller is not the super-user. [EINVAL] The address given is not page aligned or the length is negative. [ENOMEM] Some portion of the indicated address range is not allocated. SEE ALSO
fork(2), mincore(2), minherit(2), mlockall(2), mmap(2), munlockall(2), munmap(2), setrlimit(2), getpagesize(3) HISTORY
The mlock() and munlock() system calls first appeared in 4.4BSD. BUGS
Allocating too much wired memory can lead to a memory-allocation deadlock which requires a reboot to recover from. The per-process resource limit is a limit on the amount of virtual memory locked, while the system-wide limit is for the number of locked physical pages. Hence a process with two distinct locked mappings of the same physical page counts as 2 pages against the per-process limit and as only a single page in the system limit. The per-process resource limit is not currently supported. BSD
August 10, 2004 BSD

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