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Memory allocation for particular process in UNIX
Post 302936598 by Corona688 on Thursday 26th of February 2015 02:12:08 PM
02-26-2015
It has a real machine. 
It's not really a block of memory. It's all translated from virtual addresses to real addresses. Both the stack and the heap are automatically "sized" through the magic of virtual memory. The kernel itself, behind the scenes, cares very little about which is which -- it just assigns memory in fixed-sized blocks from the pile. See The Paging Game for a general explanation on how paging works.
Agreed. There's no java VM to worry about, only the kernel itself. You use it, and the kernel either lets you or not.
It doesn't get "handed back", though. Your program keeps it for later, just in case you need to allocate again -- this makes it faster, and probably why he wanted to preallocate, but the kernel handles this for you.
Check out setrlimit.
Quote:
The C virtual machine has a call stack and a heap formed at opposite ends of the same memory block. The stack may have a fixed size, but the heap is everything else.
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If you need memory you use it and hand it back when done.
It doesn't get "handed back", though. Your program keeps it for later, just in case you need to allocate again -- this makes it faster, and probably why he wanted to preallocate, but the kernel handles this for you.
Quote:
There's no portable way to put an upper limit on the heap.
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LEARN ABOUT MINIX
malloc_trim
MALLOC_TRIM(3) Linux Programmer's Manual MALLOC_TRIM(3) NAME
malloc_trim - release free memory from the top of the heap SYNOPSIS
#include <malloc.h> int malloc_trim(size_t pad); DESCRIPTION
The malloc_trim() function attempts to release free memory at the top of the heap (by calling sbrk(2) with a suitable argument). The pad argument specifies the amount of free space to leave untrimmed at the top of the heap. If this argument is 0, only the minimum amount of memory is maintained at the top of the heap (i.e., one page or less). A nonzero argument can be used to maintain some trailing space at the top of the heap in order to allow future allocations to be made without having to extend the heap with sbrk(2). RETURN VALUE
The malloc_trim() function returns 1 if memory was actually released back to the system, or 0 if it was not possible to release any memory. ERRORS
No errors are defined. ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). +--------------+---------------+---------+ |Interface | Attribute | Value | +--------------+---------------+---------+ |malloc_trim() | Thread safety | MT-Safe | +--------------+---------------+---------+ CONFORMING TO
This function is a GNU extension. NOTES
This function is automatically called by free(3) in certain circumstances; see the discussion of M_TOP_PAD and M_TRIM_THRESHOLD in mal- lopt(3). This function cannot release free memory located at places other than the top of the heap. This function releases only memory in the main arena. SEE ALSO
sbrk(2), malloc(3), mallopt(3) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 MALLOC_TRIM(3)