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Operating Systems Solaris Monitoring Paging and Swapping Post 303027403 by jlliagre on Friday 14th of December 2018 05:11:03 PM
Old 12-14-2018
Yes, a process needs not to steal memory from another process given the fact that for it to be able to use memory, it first needs to perform a successful allocation.

A process only deals with virtual memory. Memory allocated with malloc or mmap is by definition always contiguous in the process virtual space (it has an address and a size). Malloc can use brk or mmap system call to get space. Malloc'd areas might be anywhere in the process virtual space. When this virtual space is fragmented and limited (32 bit processes), a large allocation might fail even if smaller than the sum of total free space.

Contiguous virtual memory pages are mapped to physical pages. The latter don't have to be physically contiguous. That wouldn't make sense as physical pages can be on RAM and later on disk and later again, somewhere else on RAM.

A process virtual space is unrelated to another process virtual space, the same addresses can be used on either side but map to different physical pages.
 

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mlockall(2)							System Calls Manual						       mlockall(2)

NAME
mlockall() - lock a process virtual address space in memory SYNOPSIS
DESCRIPTION
The system call allows the calling process to lock its entire virtual address space into memory, making it immune to all routine swapping. flags may be one or both of the following: Lock the current process virtual address space. All addressable pages of the address space are locked. Lock any future additions to the process virtual address space. Note that does not imply or can be used to unlock all or a portion of the address space locked with A single call to removes all locks from the process virtual address space. An call results in only the specified pages being unlocked. Regardless of how many times a process locks a page, a single or will unlock it. When memory is shared by multiple processes and mlocks are applied to the same physical page by multiple processes, a page remains locked until the last lock is removed from that page. Locks and applied with are not inherited by a child process. The user must have the privilege. Although and the family of functions may be used together in an application, each may affect the other in unexpected ways. This practice is not recommended. Security Restrictions Some or all of the actions associated with this system call require the privilege. Processes owned by the superuser have this privilege. Processes owned by other users may have this privilege, depending on system configuration. See privileges(5) for more information about privileged access on systems that support fine-grained privileges. RETURN VALUE
returns the following values: Successful completion. Failure. The requested operation is not performed. is set to indicate the error. ERRORS
If fails, is set to one of the following values: The flags field did not contain either and/or There is not enough lockable memory in the system to satisfy the locking request. The user does not have the privilege. EXAMPLES
The following call to locks the entire process virtual address space in memory and ensures that any future additions to the address space will also be locked in memory: SEE ALSO
setprivgrp(1M), getprivgrp(2), mlock(2), munlock(2), munlockall(2), plock(2), privileges(5). STANDARDS CONFORMANCE
mlockall(2)
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