mallinfo man page on Archlinux

Man page or keyword search:  
man Server   11224 pages
apropos Keyword Search (all sections)
Output format
Archlinux logo
[printable version]

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

       mallinfo - obtain memory allocation information

       #include <malloc.h>

       struct mallinfo mallinfo(void);

       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

       usmblks	 The "highwater mark" for allocated space—that is, the maximum
		 amount of space that was ever allocated.  This field is main‐
		 tained 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).

       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

       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‐

       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.

       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
	   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);

       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");

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

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

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

	   for (j = freeBegin; j < freeEnd; j += freeStep)

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


       mmap(2), malloc(3), malloc_info(3), malloc_stats(3), malloc_trim(3),

       This page is part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at

Linux				  2012-05-06			   MALLINFO(3)

List of man pages available for Archlinux

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net