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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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munlock(2)							System Calls Manual							munlock(2)

NAME
munlock() - unlock a segment of the process virtual address space SYNOPSIS
DESCRIPTION
The system call allows the calling process to unlock a segment of the process virtual address space that may have been previously locked with or Upon successful completion of the pages within the specified segment are subject to routine paging and/or swapping. addr must be a valid address in the process virtual address space. addr+len must also be a valid address in the process virtual address space. Pages are unlocked at page boundaries that encompass the range from addr to addr+len. If any address within the range is not a valid part of the process virtual address space, an error is returned and no unlocks are performed. However, no error is reported for valid pages within the range that are not already locked, since their state at the completion of the call is as desired. Regardless of how many times a process locks a page, a single or will unlock it. An of a page within a range specified in an call results in only the range specified in the being unlocked. 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. The effective user ID of the calling process must be that of a user with 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: One or more addresses in the specified range is not valid within the process address space. The parameter was zero. The effective user ID of the calling process is not that of a user with the privilege. EXAMPLES
The following call to unlocks the first 10 pages of the calling process address space: SEE ALSO
setprivgrp(1M), getprivgrp(2), mlock(2), mlockall(2), munlockall(2), plock(2), privileges(5). STANDARDS CONFORMANCE
munlock(2)
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