malloc, free, realloc, reallocf, MALLOC_DEFINE, MALLOC_DECLARE — kernel memory management routines

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.

       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 memory 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 identically 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.

       The  malloc_usable_size()  function  returns  the  usable size of the allocation pointed to by addr.  The
       return value may be larger than the size that was requested during allocation.

       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 memory 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
               context.

       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 multiplication 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 satisfy 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 executable
               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 structmalloc_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>.

       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 message.

       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.

       malloc, free, realloc, reallocf, MALLOC_DEFINE, MALLOC_DECLARE — kernel memory management routines

       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).

numa(4), vmstat(8), contigmalloc(9), domainset(9), memguard(9), vnode(9)

Debian                                           August 28, 2020                                       MALLOC(9)

#include<sys/types.h>#include<sys/malloc.h>void*malloc(size_tsize, structmalloc_type*type, intflags);

       void*mallocarray(size_tnmemb, size_tsize, structmalloc_type*type, intflags);

       voidfree(void*addr, structmalloc_type*type);

       void*realloc(void*addr, size_tsize, structmalloc_type*type, intflags);

       void*reallocf(void*addr, size_tsize, structmalloc_type*type, intflags);

       size_tmalloc_usable_size(constvoid*addr);

       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_tsize, structmalloc_type*type, structdomainset*ds, intflags);

       voidfree_domain(void*addr, structmalloc_type*type);