11-24-2012
Is virtual memory so precious? about brk()
We know for every process, it has 4G virtual memory on a 32bit machine.
since virtual memory is not physical memory, why don't operating system allocate all it's virtual memory to it, but set a "program break" to limit it's heap space?
Even if the operating system allocate all the 4G virtual memory to a process, only when the process access an address that not mapped into physical memory, the OS allocate physical memory to it. So, what is the reason to limit a process's virtual memory space by "program break"?
Thanks.
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LEARN ABOUT DEBIAN
tau_track_memory_headroom
TAU_TRACK_MEMORY_HEA(3) TAU Instrumentation API TAU_TRACK_MEMORY_HEA(3)
NAME
TAU_TRACK_MEMORY_HEADROOM - Track the headroom (amount of memory for a process to grow) by periodically interrupting the program
SYNOPSIS
C/C++:
TAU_TRACK_MEMORY_HEADROOM(void);
Fortran:
TAU_TRACK_MEMORY_HEADROOM(void);
DESCRIPTION
Tracks the amount of memory available for the process before it runs out of free memory on the heap. This call sets up a signal handler
that is invoked every 10 seconds by an interrupt (this interval may be altered by using the TAU_SET_INTERRUPT_INTERVAL call). Inside the
interrupt handler, TAU evaluates how much memory it can allocate and associates it with the callstack using the TAU context events (See
TAU_REGISTER_CONTEXT_EVENT(3)). The user can vary the size of the callstack by setting the environment variable TAU_CALLPATH_DEPTH (default
is 2). This call is useful on machines like IBM BG/L where no virtual memory (or paging using the swap space) is present. The amount of
heap memory available to the program is limited by the amount of available physical memory. TAU executes a series of malloc calls with a
granularity of 1MB and determines the amount of memory available for the program to grow.
EXAMPLE
C/C++ :
TAU_TRACK_MEMORY_HEADROOM();
Fortran :
call TAU_TRACK_MEMORY_HEADROOM()
SEE ALSO
TAU_TRACK_MEMORY(3), TAU_SET_INTERRUPT_INTERVAL(3), TAU_ENABLE_TRACKING_MEMORY_HEADROOM(3), TAU_DISABLE_TRACKING_MEMORY_HEADROOM(3),
TAU_TRACK_MEMORY_HEADROOM_HERE(3)
08/31/2005 TAU_TRACK_MEMORY_HEA(3)