QMALLOC(9) QMALLOC(9)
NAME
qmalloc - quickfit malloc malloc, mallocz, smalloc, realloc,
calloc, free, msize, setmalloctag, setrealloctag,
getmalloctag, getrealloctag, mallocinit, mallocsummary -
quickfit kernel memory allocator
SYNOPSIS
void* malloc(usize size)
void* mallocalign(usize size, usize align, long offset,
usize span)
void* mallocz(usize size, int clr)
void* smalloc(usize size)
void* realloc(void *p, usize size)
void* calloc(ulong n, usize szelem)
void free(void *ptr)
ulong msize(void *ptr)
void setmalloctag(void *ptr, ulong tag)
ulong getmalloctag(void *ptr)
void setrealloctag(void *ptr, ulong tag)
ulong getrealloctag(void *ptr)
void mallocinit(void) void mallocsummary(void)
DESCRIPTION
These are kernel versions of the functions in malloc(2).
They allocate memory with Quickfit with an allocator from
Kernighan & Ritchie. The allocation is currently fixed, but
could call physalloc(9nix) in the future. All but smalloc
(which calls sleep(9)) may safely be called by interrupt
handlers.
Malloc returns a pointer to a block of at least size bytes,
initialised to zero. The block is suitably aligned for
storage of any type of object. The call malloc(0) returns a
valid pointer rather than null. Mallocz is similar, but
only clears the memory if clr is non-zero.
Smalloc returns a pointer to a block of size bytes, ini-
tialised to zero. If the memory is not immediately
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QMALLOC(9) QMALLOC(9)
available, smalloc retries every 100 milliseconds until the
memory is acquired.
Mallocalign allocates a block of at least n bytes of memory
respecting alignment contraints. If align is non-zero, the
returned pointer is aligned to be equal to offset modulo
align. If span is non-zero, the n byte block allocated will
not span a span-byte boundary.
Realloc changes the size of the block pointed to by p to
size bytes, if possible without moving the data, and returns
a pointer to the block. The contents are unchanged up to
the lesser of old and new sizes, and any new space allocated
is initialised to zero. Realloc takes on special meanings
when one or both arguments are zero:
realloc(0, size)
means `malloc(size)'; returns a pointer to the newly-
allocated memory
realloc(ptr, 0)
means `free(ptr)'; returns null
realloc(0, 0)
no-op; returns null
Calloc returns a pointer to a block of memory of at least
n*szelem bytes, initialised to zero. New code should use
mallocz instead.
The argument to free is a pointer to a block of memory allo-
cated by one of the routines above, which is returned to the
allocation pool, or a null pointer, which is ignored.
When a block is allocated, sometimes there is some extra
unused space at the end. Msize grows the block to encompass
this unused space and returns the new number of bytes that
may be used.
The memory allocator does not maintain ``malloc tag'' and
the ``realloc tag'', but the functions setmalloctag,
getmalloctag, setrealloctag, and getrealloctag are provided
for compaibility with the pool(2) library.
Mallocinit must be called before malloc is used.
Mallocsummary prints a short summary of the allocator's
state on the console.
SOURCE
/sys/src/9/port/qmalloc.c
/sys/src/nix/port/qmalloc.c
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DIAGNOSTICS
All functions except smalloc return a null pointer if space
is unavailable.
SEE ALSO
The C Programming Language, 2ed, Brian Kernighan and Dennis
Ritchie, chapter 8 §7: Example—Storage Allocator.
Quickfit: An efficient algorithm for heap storage
allocation" , Charles B. Weinstock and William A. Wulf. ACM
SIGPLAN Notices, 23(10):141—144, October 1988.
pool(2), physalloc(9nix)
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