svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
malloc(9)
MALLOC(9) BSD Kernel Developer's Manual MALLOC(9)
NAME
malloc, free, realloc, reallocf, MALLOC_DEFINE, MALLOC_DECLARE — kernel
memory management routines
SYNOPSIS
#include <sys/types.h>
#include <sys/malloc.h>
void *
malloc(size_t size, struct malloc_type *type, int flags);
void *
mallocarray(size_t nmemb, size_t size, struct malloc_type *type,
int flags);
void
free(void *addr, struct malloc_type *type);
void *
realloc(void *addr, size_t size, struct malloc_type *type, int flags);
void *
reallocf(void *addr, size_t size, struct malloc_type *type, int flags);
MALLOC_DECLARE(type);
#include <sys/param.h>
#include <sys/malloc.h>
#include <sys/kernel.h>
MALLOC_DEFINE(type, shortdesc, longdesc);
#include <sys/param.h>
#include <sys/domainset.h>
void *
malloc_domainset(size_t size, struct malloc_type *type,
struct domainset *ds, int flags);
void
free_domain(void *addr, struct malloc_type *type);
DESCRIPTION
The malloc() function allocates uninitialized memory in kernel address
space for an object whose size is specified by size.
The malloc_domainset() variant allocates memory from a specific numa(4)
domain using the specified domain selection policy. See domainset(9) for
some example policies. Memory allocated with this function should be
returned with free_domain().
The mallocarray() function allocates uninitialized memory in kernel
address space for an array of nmemb entries whose size is specified by
size.
The free() function releases memory at address addr that was previously
allocated by malloc() for re-use. The memory is not zeroed. If addr is
NULL, then free() does nothing.
The realloc() function changes the size of the previously allocated mem‐
ory referenced by addr to size bytes. The contents of the memory are
unchanged up to the lesser of the new and old sizes. Note that the
returned value may differ from addr. If the requested memory cannot be
allocated, NULL is returned and the memory referenced by addr is valid
and unchanged. If addr is NULL, the realloc() function behaves identi‐
cally to malloc() for the specified size.
The reallocf() function is identical to realloc() except that it will
free the passed pointer when the requested memory cannot be allocated.
Unlike its standard C library counterpart (malloc(3)), the kernel version
takes two more arguments. The flags argument further qualifies
malloc()'s operational characteristics as follows:
M_ZERO Causes the allocated memory to be set to all zeros.
M_NODUMP
For allocations greater than page size, causes the allocated mem‐
ory to be excluded from kernel core dumps.
M_NOWAIT
Causes malloc(), realloc(), and reallocf() to return NULL if the
request cannot be immediately fulfilled due to resource shortage.
Note that M_NOWAIT is required when running in an interrupt con‐
text.
M_WAITOK
Indicates that it is OK to wait for resources. If the request
cannot be immediately fulfilled, the current process is put to
sleep to wait for resources to be released by other processes.
The malloc(), mallocarray(), realloc(), and reallocf() functions
cannot return NULL if M_WAITOK is specified. If the multiplica‐
tion of nmemb and size would cause an integer overflow, the
mallocarray() function induces a panic.
M_USE_RESERVE
Indicates that the system can use its reserve of memory to sat‐
isfy the request. This option should only be used in combination
with M_NOWAIT when an allocation failure cannot be tolerated by
the caller without catastrophic effects on the system.
M_EXEC Indicates that the system should allocate executable memory. If
this flag is not set, the system will not allocate executable
memory. Not all platforms enforce a distinction between exe‐
cutable and non-executable memory.
Exactly one of either M_WAITOK or M_NOWAIT must be specified.
The type argument is used to perform statistics on memory usage, and for
basic sanity checks. It can be used to identify multiple allocations.
The statistics can be examined by ‘vmstat -m’.
A type is defined using struct malloc_type via the MALLOC_DECLARE() and
MALLOC_DEFINE() macros.
/* sys/something/foo_extern.h */
MALLOC_DECLARE(M_FOOBUF);
/* sys/something/foo_main.c */
MALLOC_DEFINE(M_FOOBUF, "foobuffers", "Buffers to foo data into the ether");
/* sys/something/foo_subr.c */
...
buf = malloc(sizeof(*buf), M_FOOBUF, M_NOWAIT);
In order to use MALLOC_DEFINE(), one must include <sys/param.h> (instead
of <sys/types.h>) and <sys/kernel.h>.
CONTEXT
malloc(), realloc() and reallocf() may not be called from fast interrupts
handlers. When called from threaded interrupts, flags must contain
M_NOWAIT.
malloc(), realloc() and reallocf() may sleep when called with M_WAITOK.
free() never sleeps. However, malloc(), realloc(), reallocf() and free()
may not be called in a critical section or while holding a spin lock.
Any calls to malloc() (even with M_NOWAIT) or free() when holding a
vnode(9) interlock, will cause a LOR (Lock Order Reversal) due to the
intertwining of VM Objects and Vnodes.
IMPLEMENTATION NOTES
The memory allocator allocates memory in chunks that have size a power of
two for requests up to the size of a page of memory. For larger
requests, one or more pages is allocated. While it should not be relied
upon, this information may be useful for optimizing the efficiency of
memory use.
RETURN VALUES
The malloc(), realloc(), and reallocf() functions return a kernel virtual
address that is suitably aligned for storage of any type of object, or
NULL if the request could not be satisfied (implying that M_NOWAIT was
set).
DIAGNOSTICS
A kernel compiled with the INVARIANTS configuration option attempts to
detect memory corruption caused by such things as writing outside the
allocated area and imbalanced calls to the malloc() and free() functions.
Failing consistency checks will cause a panic or a system console mes‐
sage.
SEE ALSO
numa(4), vmstat(8), contigmalloc(9), domainset(9), memguard(9), vnode(9)
BSD October 30, 2018 BSD