MALLINFO(3) | Linux Programmer's Manual | MALLINFO(3) |
NAME
mallinfo - obtain memory allocation informationSYNOPSIS
#include <malloc.h>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 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).
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.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 standard output.
$ ./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 3.53 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/.2012-05-06 | Linux |