Solaris Page-Demand Memory Management

Pertaining Solaris Kernel Proc mgt and Memory Mgt
architecture, Heap segment within Process Virtual
Address Space is allocated for user land data structure
righ above executable data segment of the user land
DB process and grow with the libc.so.1 system
library call such as malloc(3c) which malloc_unlocked does
the dirty work to allocate holding blocks or ordinary
blocks for user land process. If there is no block sbrk(3c) is
called.

It is transparent zero-fill-on-demand memory page
allocation because of the page fault.
Page memory is allocated for the process heap and
space becomes a permanently allocated block.

(1) However, the allocation will not shrink until
process exits.
(2) Page scanner daemon runs to page out memory page
per LRU due to the shortage of memory

This is the core of on demand page memory management
architecture of Solaris Operating System.

As for the free(3c) which free_unlocked is doing the dirty
work to mark the address space as free list
for later use but not to return address space to memory
resource managed pool.

Solaris Basic Library

These default memory allocation routines are safe for use
in multithreaded applications but are not scalable.
Concurrent accesses by multiple threads are single-threaded
through the use of a single lock. Multithreaded applications
that make heavy use of dynamic memory allocation should be
linked with allocation libraries designed for concurrent access,
such as libumem(3LIB) or libmtmalloc(3LIB). Applications that
want to avoid using heap allocations (with brk(2)) can do so
by using either libumem or libmapmalloc(3LIB). The allocation
libraries libmalloc(3LIB) and libbsdmalloc(3LIB) are
available for special needs.