11-26-2012
Quote:
Originally Posted by
vistastar
2,don't understand
That means as I have 200 processes running like my laptop on Solaris 11, I would need more than 800 GB of RAM+swap area. This would also affect to a lesser extent most Linux installations as "always overcommit" is not the default configuration.
See this
page for some background about linux and memory overcommitment.
Quote:
3,AFAIK, on linux threads' stack is allocated on heap of the main thread and managed by thread lib.
Possibly but that was just an example. Other memory parts are neither heap nor stack, like mmaped areas (eg: shared libraries).
Quote:
4,if the operating system allocate a very large heap to a process, and malloc knows it has all the heap space, then it can also use the way it like.
Malloc can already use the whole heap space the way it likes as brk() is a cheap operation. Having all of it allocated at startup like you suggest wouldn't make that much of a difference on that side but there is no much point wasting resources, even virtual ones.
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LEARN ABOUT X11R4
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)