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 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).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). Interface Attribute Value mallinfo() Thread safety MT-Unsafe init const:mallopt mallinfo() would access some global internal objects. If modify them with non-atomically, may get inconsistent results. The identifier mallopt in const:mallopt mean that mallopt() would modify the global internal objects with atomics, that make sure mallinfo() is safe enough, others modify with non-atomically maybe not.
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 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 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 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
