mallinfo


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).

       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

       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)

COLOPHON
       This page is part of release 3.54 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)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2018 Hurricane Electric. All Rights Reserved.