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Linux 2.6 - man page for mallinfo (linux section 3)

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 information 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 maximum amount	of  space
		 that was ever allocated.  This field is maintained only in nonthreading environ-
		 ments.

       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).

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 malloc_info(3) for alternatives that include
       information about other arenas.

       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 statistics before and
       after allocating and freeing some blocks of memory.  The statistics are displayed on stan-
       dard 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 position 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 3.55 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at
       http://www.kernel.org/doc/man-pages/.

Linux					    2012-05-06				      MALLINFO(3)


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