NAME
mallinfo - obtain memory allocation information SYNOPSIS
#include
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 MMMAPTHRESHOLD 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 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 malloctrim(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 mallocstats(3) and mal‐ locinfo(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
#include "tlpihdr.h" static void displaymallinfo(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 MAXALLOCS 2000000 char *alloc[MAXALLOCS]; int numBlocks, j, freeBegin, freeEnd, freeStep; sizet 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"); displaymallinfo(); for (j = 0; j < numBlocks; j++) { if (numBlocks >= MAXALLOCS) fatal("Too many allocations"); alloc[j] = malloc(blockSize); if (alloc[j] == NULL) errExit("malloc"); } printf("\n============== After allocating blocks ==============\n"); displaymallinfo(); for (j = freeBegin; j < freeEnd; j += freeStep) free(alloc[j]); printf("\n============== After freeing blocks ==============\n"); displaymallinfo(); exit(EXITSUCCESS); } SEE ALSO mmap(2), malloc(3), mallocinfo(3), mallocstats(3), malloctrim(3), mallopt(3) COLOPHON
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Linux 2012-05-06 MALLINFO(3)