MALLOC(9)              386BSD Kernel Programmer's Manual             MALLOC(9)

NAME
     malloc - kernel dynamic memory allocator

SYNOPSIS
     #include "malloc.h"

     void *
     malloc(u_long size, int type, int flags)

     void
     free(void *addr, int type)

DESCRIPTION
     Most shared resources in the 386BSD kernel are dynamically allocated on
     demand to serve need (with administrative bounds present to avoid system
     overrun). The malloc() function is used to allocate small (<= 64KB)
     portions of memory in the kernel, and is especially useful in sub-page
     sized allocations, since it maintains a free pool of page fragments to
     allocate from.

     While this function superfically resembles the user mode malloc(3)
     function, it has two additional arguments.  Associated with each
     allocation is a type which tags allocations of a given kind for use in
     statistics and run-away allocation prevention. In addition, malloc() has
     a flags argument to select optional handling (M_NOWAIT is the most common
     option, allowing the function to be used from interrupt level by
     disallowing a block if no space available).

     The malloc() function obtains memory for its pool from the virtual memory
     system via the kmem(9) facility.

     The free() function returns used memory to the memory pool. If a surplus
     of memory is present in the allocator's pool, it will attempt to return
     whole pages back to the kmem(9) facility. As such, it defers to the
     virtual memory system as the primary location where memory resource
     resides.

     Since the virtual memory system itself makes use of malloc() for its
     operation, care is taken to avoid recursion.

RETURN VALUES
     The malloc() function returns a address of the allocated resource if
     successful; otherwise a null address is returned.

SEE ALSO
     kmem(9)

386BSD Release 1.0              August 29, 1994                              1