MALLINFO(3)		   Linux Programmer's Manual		   MALLINFO(3)



NAME
       mallinfo - obtain memory allocation information

SYNOPSIS
       #include <malloc.h>

       struct mallinfo mallinfo(void);

DESCRIPTION
       The mallinfo() function returns a copy of a structure containing infor-
       mation about memory allocations	performed  by  malloc(3)  and  related
       functions.  This structure is defined as follows:

	   struct mallinfo {
	       int arena;     /* Non-mmapped space allocated (bytes) */
	       int ordblks;   /* Number of free chunks */
	       int smblks;    /* Number of free fastbin blocks */
	       int hblks;     /* Number of mmapped regions */
	       int hblkhd;    /* Space allocated in mmapped regions (bytes) */
	       int usmblks;   /* Maximum total allocated space (bytes) */
	       int fsmblks;   /* Space in freed fastbin blocks (bytes) */
	       int uordblks;  /* Total allocated space (bytes) */
	       int fordblks;  /* Total free space (bytes) */
	       int keepcost;  /* Top-most, releasable space (bytes) */
	   };

       The fields of the mallinfo structure contain the following information:

       arena	 The  total  amount  of	 memory	 allocated by means other than
		 mmap(2) (i.e., memory allocated on the	 heap).	  This	figure
		 includes both in-use blocks and blocks on the free list.

       ordblks	 The number of ordinary (i.e., non-fastbin) free blocks.

       smblks	 The number of fastbin free blocks (see mallopt(3)).

       hblks	 The number of blocks currently allocated using mmap(2).  (See
		 the discussion of M_MMAP_THRESHOLD in mallopt(3).)

       hblkhd	 The number of	bytes  in  blocks  currently  allocated	 using
		 mmap(2).

       usmblks	 The  "highwater mark" for allocated space--that is, the maxi-
		 mum amount of space that was ever allocated.  This  field  is
		 maintained only in nonthreading environments.

       fsmblks	 The total number of bytes in fastbin free blocks.

       uordblks	 The total number of bytes used by in-use allocations.

       fordblks	 The total number of bytes in free blocks.

       keepcost	 The  total  amount of releasable free space at the top of the
		 heap.	This is the maximum number of bytes that could ideally
		 (i.e.,	 ignoring  page	 alignment restrictions, and so on) be
		 released by malloc_trim(3).

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +-----------+---------------+------------------------------+
       |Interface  | Attribute	   | Value			  |
       +-----------+---------------+------------------------------+
       |mallinfo() | Thread safety | MT-Unsafe init const:mallopt |
       +-----------+---------------+------------------------------+
       mallinfo()  would  access some global internal objects.	If modify them
       with non-atomically, may get inconsistent results.  The identifier mal-
       lopt  in	 const:mallopt	mean  that  mallopt()  would modify the global
       internal objects with  atomics,	that  make  sure  mallinfo()  is  safe
       enough, others modify with non-atomically maybe not.

CONFORMING TO
       This  function is not specified by POSIX or the C standards.  A similar
       function exists on many System V derivatives, and was specified in  the
       SVID.

BUGS
       Information  is	returned  for  only  the  main memory allocation area.
       Allocations in other arenas are excluded.  See malloc_stats(3) and mal-
       loc_info(3)  for alternatives that include information about other are-
       nas.

       The fields of the  mallinfo  structure  are  typed  as  int.   However,
       because	some  internal	bookkeeping  values  may  be of type long, the
       reported values may wrap around zero and thus be inaccurate.

EXAMPLE
       The program below employs mallinfo() to retrieve memory allocation sta-
       tistics	before and after allocating and freeing some blocks of memory.
       The statistics are displayed on standard output.

       The first two command-line arguments specify the	 number	 and  size  of
       blocks to be allocated with malloc(3).

       The  remaining  three  arguments	 specify which of the allocated blocks
       should be freed with free(3).  These three arguments are optional,  and
       specify	(in  order):  the  step size to be used in the loop that frees
       blocks (the default is 1, meaning free all blocks in  the  range);  the
       ordinal position of the first block to be freed (default 0, meaning the
       first allocated block); and a number one greater than the ordinal posi-
       tion  of	 the  last  block to be freed (default is one greater than the
       maximum block number).  If these three arguments are omitted, then  the
       defaults cause all allocated blocks to be freed.

       In  the	following  example run of the program, 1000 allocations of 100
       bytes are performed, and then every second allocated block is freed:

	   $ ./a.out 1000 100 2
	   ============== Before allocating blocks ==============
	   Total non-mmapped bytes (arena):	  0
	   # of free chunks (ordblks):		  1
	   # of free fastbin blocks (smblks):	  0
	   # of mapped regions (hblks):		  0
	   Bytes in mapped regions (hblkhd):	  0
	   Max. total allocated space (usmblks):  0
	   Free bytes held in fastbins (fsmblks): 0
	   Total allocated space (uordblks):	  0
	   Total free space (fordblks):		  0
	   Topmost releasable block (keepcost):	  0

	   ============== After allocating blocks ==============
	   Total non-mmapped bytes (arena):	  135168
	   # of free chunks (ordblks):		  1
	   # of free fastbin blocks (smblks):	  0
	   # of mapped regions (hblks):		  0
	   Bytes in mapped regions (hblkhd):	  0
	   Max. total allocated space (usmblks):  0
	   Free bytes held in fastbins (fsmblks): 0
	   Total allocated space (uordblks):	  104000
	   Total free space (fordblks):		  31168
	   Topmost releasable block (keepcost):	  31168

	   ============== After freeing blocks ==============
	   Total non-mmapped bytes (arena):	  135168
	   # of free chunks (ordblks):		  501
	   # of free fastbin blocks (smblks):	  0
	   # of mapped regions (hblks):		  0
	   Bytes in mapped regions (hblkhd):	  0
	   Max. total allocated space (usmblks):  0
	   Free bytes held in fastbins (fsmblks): 0
	   Total allocated space (uordblks):	  52000
	   Total free space (fordblks):		  83168
	   Topmost releasable block (keepcost):	  31168

   Program source

       #include <malloc.h>
       #include "tlpi_hdr.h"

       static void
       display_mallinfo(void)
       {
	   struct mallinfo mi;

	   mi = mallinfo();

	   printf("Total non-mmapped bytes (arena):	  %d\n", mi.arena);
	   printf("# of free chunks (ordblks):		  %d\n", mi.ordblks);
	   printf("# of free fastbin blocks (smblks):	  %d\n", mi.smblks);
	   printf("# of mapped regions (hblks):		  %d\n", mi.hblks);
	   printf("Bytes in mapped regions (hblkhd):	  %d\n", mi.hblkhd);
	   printf("Max. total allocated space (usmblks):  %d\n", mi.usmblks);
	   printf("Free bytes held in fastbins (fsmblks): %d\n", mi.fsmblks);
	   printf("Total allocated space (uordblks):	  %d\n", mi.uordblks);
	   printf("Total free space (fordblks):		  %d\n", mi.fordblks);
	   printf("Topmost releasable block (keepcost):	  %d\n", mi.keepcost);
       }

       int
       main(int argc, char *argv[])
       {
       #define MAX_ALLOCS 2000000
	   char *alloc[MAX_ALLOCS];
	   int numBlocks, j, freeBegin, freeEnd, freeStep;
	   size_t blockSize;

	   if (argc < 3 || strcmp(argv[1], "--help") == 0)
	       usageErr("%s num-blocks block-size [free-step [start-free "
		       "[end-free]]]\n", argv[0]);

	   numBlocks = atoi(argv[1]);
	   blockSize = atoi(argv[2]);
	   freeStep = (argc > 3) ? atoi(argv[3]) : 1;
	   freeBegin = (argc > 4) ? atoi(argv[4]) : 0;
	   freeEnd = (argc > 5) ? atoi(argv[5]) : numBlocks;

	   printf("============== Before allocating blocks ==============\n");
	   display_mallinfo();

	   for (j = 0; j < numBlocks; j++) {
	       if (numBlocks >= MAX_ALLOCS)
		   fatal("Too many allocations");

	       alloc[j] = malloc(blockSize);
	       if (alloc[j] == NULL)
		   errExit("malloc");
	   }

	   printf("\n============== After allocating blocks ==============\n");
	   display_mallinfo();

	   for (j = freeBegin; j < freeEnd; j += freeStep)
	       free(alloc[j]);

	   printf("\n============== After freeing blocks ==============\n");
	   display_mallinfo();

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       mmap(2), malloc(3), malloc_info(3), malloc_stats(3), malloc_trim(3),
       mallopt(3)

COLOPHON
       This page is part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux				  2015-12-05			   MALLINFO(3)