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           #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
           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
           statistics  before and after allocating and freeing some blocks of mem-
           ory.  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
           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");

    Linux 2012-05-06 MALLINFO(3)


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