1/* 2 A version of malloc/free/realloc written by Doug Lea and released to the 3 public domain. Send questions/comments/complaints/performance data 4 to dl@cs.oswego.edu 5 6* VERSION 2.6.6 Sun Mar 5 19:10:03 2000 Doug Lea (dl at gee) 7 8 Note: There may be an updated version of this malloc obtainable at 9 ftp://g.oswego.edu/pub/misc/malloc.c 10 Check before installing! 11 12* Why use this malloc? 13 14 This is not the fastest, most space-conserving, most portable, or 15 most tunable malloc ever written. However it is among the fastest 16 while also being among the most space-conserving, portable and tunable. 17 Consistent balance across these factors results in a good general-purpose 18 allocator. For a high-level description, see 19 http://g.oswego.edu/dl/html/malloc.html 20 21* Synopsis of public routines 22 23 (Much fuller descriptions are contained in the program documentation below.) 24 25 malloc(size_t n); 26 Return a pointer to a newly allocated chunk of at least n bytes, or null 27 if no space is available. 28 free(Void_t* p); 29 Release the chunk of memory pointed to by p, or no effect if p is null. 30 realloc(Void_t* p, size_t n); 31 Return a pointer to a chunk of size n that contains the same data 32 as does chunk p up to the minimum of (n, p's size) bytes, or null 33 if no space is available. The returned pointer may or may not be 34 the same as p. If p is null, equivalent to malloc. Unless the 35 #define REALLOC_ZERO_BYTES_FREES below is set, realloc with a 36 size argument of zero (re)allocates a minimum-sized chunk. 37 memalign(size_t alignment, size_t n); 38 Return a pointer to a newly allocated chunk of n bytes, aligned 39 in accord with the alignment argument, which must be a power of 40 two. 41 valloc(size_t n); 42 Equivalent to memalign(pagesize, n), where pagesize is the page 43 size of the system (or as near to this as can be figured out from 44 all the includes/defines below.) 45 pvalloc(size_t n); 46 Equivalent to valloc(minimum-page-that-holds(n)), that is, 47 round up n to nearest pagesize. 48 calloc(size_t unit, size_t quantity); 49 Returns a pointer to quantity * unit bytes, with all locations 50 set to zero. 51 cfree(Void_t* p); 52 Equivalent to free(p). 53 malloc_trim(size_t pad); 54 Release all but pad bytes of freed top-most memory back 55 to the system. Return 1 if successful, else 0. 56 malloc_usable_size(Void_t* p); 57 Report the number usable allocated bytes associated with allocated 58 chunk p. This may or may not report more bytes than were requested, 59 due to alignment and minimum size constraints. 60 malloc_stats(); 61 Prints brief summary statistics on stderr. 62 mallinfo() 63 Returns (by copy) a struct containing various summary statistics. 64 mallopt(int parameter_number, int parameter_value) 65 Changes one of the tunable parameters described below. Returns 66 1 if successful in changing the parameter, else 0. 67 68* Vital statistics: 69 70 Alignment: 8-byte 71 8 byte alignment is currently hardwired into the design. This 72 seems to suffice for all current machines and C compilers. 73 74 Assumed pointer representation: 4 or 8 bytes 75 Code for 8-byte pointers is untested by me but has worked 76 reliably by Wolfram Gloger, who contributed most of the 77 changes supporting this. 78 79 Assumed size_t representation: 4 or 8 bytes 80 Note that size_t is allowed to be 4 bytes even if pointers are 8. 81 82 Minimum overhead per allocated chunk: 4 or 8 bytes 83 Each malloced chunk has a hidden overhead of 4 bytes holding size 84 and status information. 85 86 Minimum allocated size: 4-byte ptrs: 16 bytes (including 4 overhead) 87 8-byte ptrs: 24/32 bytes (including, 4/8 overhead) 88 89 When a chunk is freed, 12 (for 4byte ptrs) or 20 (for 8 byte 90 ptrs but 4 byte size) or 24 (for 8/8) additional bytes are 91 needed; 4 (8) for a trailing size field 92 and 8 (16) bytes for free list pointers. Thus, the minimum 93 allocatable size is 16/24/32 bytes. 94 95 Even a request for zero bytes (i.e., malloc(0)) returns a 96 pointer to something of the minimum allocatable size. 97 98 Maximum allocated size: 4-byte size_t: 2^31 - 8 bytes 99 8-byte size_t: 2^63 - 16 bytes 100 101 It is assumed that (possibly signed) size_t bit values suffice to 102 represent chunk sizes. `Possibly signed' is due to the fact 103 that `size_t' may be defined on a system as either a signed or 104 an unsigned type. To be conservative, values that would appear 105 as negative numbers are avoided. 106 Requests for sizes with a negative sign bit when the request 107 size is treaded as a long will return null. 108 109 Maximum overhead wastage per allocated chunk: normally 15 bytes 110 111 Alignnment demands, plus the minimum allocatable size restriction 112 make the normal worst-case wastage 15 bytes (i.e., up to 15 113 more bytes will be allocated than were requested in malloc), with 114 two exceptions: 115 1. Because requests for zero bytes allocate non-zero space, 116 the worst case wastage for a request of zero bytes is 24 bytes. 117 2. For requests >= mmap_threshold that are serviced via 118 mmap(), the worst case wastage is 8 bytes plus the remainder 119 from a system page (the minimal mmap unit); typically 4096 bytes. 120 121* Limitations 122 123 Here are some features that are NOT currently supported 124 125 * No user-definable hooks for callbacks and the like. 126 * No automated mechanism for fully checking that all accesses 127 to malloced memory stay within their bounds. 128 * No support for compaction. 129 130* Synopsis of compile-time options: 131 132 People have reported using previous versions of this malloc on all 133 versions of Unix, sometimes by tweaking some of the defines 134 below. It has been tested most extensively on Solaris and 135 Linux. It is also reported to work on WIN32 platforms. 136 People have also reported adapting this malloc for use in 137 stand-alone embedded systems. 138 139 The implementation is in straight, hand-tuned ANSI C. Among other 140 consequences, it uses a lot of macros. Because of this, to be at 141 all usable, this code should be compiled using an optimizing compiler 142 (for example gcc -O2) that can simplify expressions and control 143 paths. 144 145 __STD_C (default: derived from C compiler defines) 146 Nonzero if using ANSI-standard C compiler, a C++ compiler, or 147 a C compiler sufficiently close to ANSI to get away with it. 148 DEBUG (default: NOT defined) 149 Define to enable debugging. Adds fairly extensive assertion-based 150 checking to help track down memory errors, but noticeably slows down 151 execution. 152 REALLOC_ZERO_BYTES_FREES (default: NOT defined) 153 Define this if you think that realloc(p, 0) should be equivalent 154 to free(p). Otherwise, since malloc returns a unique pointer for 155 malloc(0), so does realloc(p, 0). 156 HAVE_MEMCPY (default: defined) 157 Define if you are not otherwise using ANSI STD C, but still 158 have memcpy and memset in your C library and want to use them. 159 Otherwise, simple internal versions are supplied. 160 USE_MEMCPY (default: 1 if HAVE_MEMCPY is defined, 0 otherwise) 161 Define as 1 if you want the C library versions of memset and 162 memcpy called in realloc and calloc (otherwise macro versions are used). 163 At least on some platforms, the simple macro versions usually 164 outperform libc versions. 165 HAVE_MMAP (default: defined as 1) 166 Define to non-zero to optionally make malloc() use mmap() to 167 allocate very large blocks. 168 HAVE_MREMAP (default: defined as 0 unless Linux libc set) 169 Define to non-zero to optionally make realloc() use mremap() to 170 reallocate very large blocks. 171 malloc_getpagesize (default: derived from system #includes) 172 Either a constant or routine call returning the system page size. 173 HAVE_USR_INCLUDE_MALLOC_H (default: NOT defined) 174 Optionally define if you are on a system with a /usr/include/malloc.h 175 that declares struct mallinfo. It is not at all necessary to 176 define this even if you do, but will ensure consistency. 177 INTERNAL_SIZE_T (default: size_t) 178 Define to a 32-bit type (probably `unsigned int') if you are on a 179 64-bit machine, yet do not want or need to allow malloc requests of 180 greater than 2^31 to be handled. This saves space, especially for 181 very small chunks. 182 INTERNAL_LINUX_C_LIB (default: NOT defined) 183 Defined only when compiled as part of Linux libc. 184 Also note that there is some odd internal name-mangling via defines 185 (for example, internally, `malloc' is named `mALLOc') needed 186 when compiling in this case. These look funny but don't otherwise 187 affect anything. 188 WIN32 (default: undefined) 189 Define this on MS win (95, nt) platforms to compile in sbrk emulation. 190 LACKS_UNISTD_H (default: undefined if not WIN32) 191 Define this if your system does not have a <unistd.h>. 192 LACKS_SYS_PARAM_H (default: undefined if not WIN32) 193 Define this if your system does not have a <sys/param.h>. 194 MORECORE (default: sbrk) 195 The name of the routine to call to obtain more memory from the system. 196 MORECORE_FAILURE (default: -1) 197 The value returned upon failure of MORECORE. 198 MORECORE_CLEARS (default 1) 199 True (1) if the routine mapped to MORECORE zeroes out memory (which 200 holds for sbrk). 201 DEFAULT_TRIM_THRESHOLD 202 DEFAULT_TOP_PAD 203 DEFAULT_MMAP_THRESHOLD 204 DEFAULT_MMAP_MAX 205 Default values of tunable parameters (described in detail below) 206 controlling interaction with host system routines (sbrk, mmap, etc). 207 These values may also be changed dynamically via mallopt(). The 208 preset defaults are those that give best performance for typical 209 programs/systems. 210 USE_DL_PREFIX (default: undefined) 211 Prefix all public routines with the string 'dl'. Useful to 212 quickly avoid procedure declaration conflicts and linker symbol 213 conflicts with existing memory allocation routines. 214 215 216*/ 217 218 219 220 221/* Preliminaries */ 222 223#ifndef __STD_C 224#ifdef __STDC__ 225#define __STD_C 1 226#else 227#if __cplusplus 228#define __STD_C 1 229#else 230#define __STD_C 0 231#endif /*__cplusplus*/ 232#endif /*__STDC__*/ 233#endif /*__STD_C*/ 234 235#ifndef Void_t 236#if (__STD_C || defined(WIN32)) 237#define Void_t void 238#else 239#define Void_t char 240#endif 241#endif /*Void_t*/ 242 243#if __STD_C 244#include <linux/stddef.h> /* for size_t */ 245#else 246#include <sys/types.h> 247#endif /* __STD_C */ 248 249#ifdef __cplusplus 250extern "C" { 251#endif 252 253#if 0 /* not for U-Boot */ 254#include <stdio.h> /* needed for malloc_stats */ 255#endif 256 257 258/* 259 Compile-time options 260*/ 261 262 263/* 264 Debugging: 265 266 Because freed chunks may be overwritten with link fields, this 267 malloc will often die when freed memory is overwritten by user 268 programs. This can be very effective (albeit in an annoying way) 269 in helping track down dangling pointers. 270 271 If you compile with -DDEBUG, a number of assertion checks are 272 enabled that will catch more memory errors. You probably won't be 273 able to make much sense of the actual assertion errors, but they 274 should help you locate incorrectly overwritten memory. The 275 checking is fairly extensive, and will slow down execution 276 noticeably. Calling malloc_stats or mallinfo with DEBUG set will 277 attempt to check every non-mmapped allocated and free chunk in the 278 course of computing the summmaries. (By nature, mmapped regions 279 cannot be checked very much automatically.) 280 281 Setting DEBUG may also be helpful if you are trying to modify 282 this code. The assertions in the check routines spell out in more 283 detail the assumptions and invariants underlying the algorithms. 284 285*/ 286 287#ifdef DEBUG 288/* #include <assert.h> */ 289#define assert(x) ((void)0) 290#else 291#define assert(x) ((void)0) 292#endif 293 294 295/* 296 INTERNAL_SIZE_T is the word-size used for internal bookkeeping 297 of chunk sizes. On a 64-bit machine, you can reduce malloc 298 overhead by defining INTERNAL_SIZE_T to be a 32 bit `unsigned int' 299 at the expense of not being able to handle requests greater than 300 2^31. This limitation is hardly ever a concern; you are encouraged 301 to set this. However, the default version is the same as size_t. 302*/ 303 304#ifndef INTERNAL_SIZE_T 305#define INTERNAL_SIZE_T size_t 306#endif 307 308/* 309 REALLOC_ZERO_BYTES_FREES should be set if a call to 310 realloc with zero bytes should be the same as a call to free. 311 Some people think it should. Otherwise, since this malloc 312 returns a unique pointer for malloc(0), so does realloc(p, 0). 313*/ 314 315 316/* #define REALLOC_ZERO_BYTES_FREES */ 317 318 319/* 320 WIN32 causes an emulation of sbrk to be compiled in 321 mmap-based options are not currently supported in WIN32. 322*/ 323 324/* #define WIN32 */ 325#ifdef WIN32 326#define MORECORE wsbrk 327#define HAVE_MMAP 0 328 329#define LACKS_UNISTD_H 330#define LACKS_SYS_PARAM_H 331 332/* 333 Include 'windows.h' to get the necessary declarations for the 334 Microsoft Visual C++ data structures and routines used in the 'sbrk' 335 emulation. 336 337 Define WIN32_LEAN_AND_MEAN so that only the essential Microsoft 338 Visual C++ header files are included. 339*/ 340#define WIN32_LEAN_AND_MEAN 341#include <windows.h> 342#endif 343 344 345/* 346 HAVE_MEMCPY should be defined if you are not otherwise using 347 ANSI STD C, but still have memcpy and memset in your C library 348 and want to use them in calloc and realloc. Otherwise simple 349 macro versions are defined here. 350 351 USE_MEMCPY should be defined as 1 if you actually want to 352 have memset and memcpy called. People report that the macro 353 versions are often enough faster than libc versions on many 354 systems that it is better to use them. 355 356*/ 357 358#define HAVE_MEMCPY 359 360#ifndef USE_MEMCPY 361#ifdef HAVE_MEMCPY 362#define USE_MEMCPY 1 363#else 364#define USE_MEMCPY 0 365#endif 366#endif 367 368#if (__STD_C || defined(HAVE_MEMCPY)) 369 370#if __STD_C 371void* memset(void*, int, size_t); 372void* memcpy(void*, const void*, size_t); 373#else 374#ifdef WIN32 375/* On Win32 platforms, 'memset()' and 'memcpy()' are already declared in */ 376/* 'windows.h' */ 377#else 378Void_t* memset(); 379Void_t* memcpy(); 380#endif 381#endif 382#endif 383 384#if USE_MEMCPY 385 386/* The following macros are only invoked with (2n+1)-multiples of 387 INTERNAL_SIZE_T units, with a positive integer n. This is exploited 388 for fast inline execution when n is small. */ 389 390#define MALLOC_ZERO(charp, nbytes) \ 391do { \ 392 INTERNAL_SIZE_T mzsz = (nbytes); \ 393 if(mzsz <= 9*sizeof(mzsz)) { \ 394 INTERNAL_SIZE_T* mz = (INTERNAL_SIZE_T*) (charp); \ 395 if(mzsz >= 5*sizeof(mzsz)) { *mz++ = 0; \ 396 *mz++ = 0; \ 397 if(mzsz >= 7*sizeof(mzsz)) { *mz++ = 0; \ 398 *mz++ = 0; \ 399 if(mzsz >= 9*sizeof(mzsz)) { *mz++ = 0; \ 400 *mz++ = 0; }}} \ 401 *mz++ = 0; \ 402 *mz++ = 0; \ 403 *mz = 0; \ 404 } else memset((charp), 0, mzsz); \ 405} while(0) 406 407#define MALLOC_COPY(dest,src,nbytes) \ 408do { \ 409 INTERNAL_SIZE_T mcsz = (nbytes); \ 410 if(mcsz <= 9*sizeof(mcsz)) { \ 411 INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) (src); \ 412 INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) (dest); \ 413 if(mcsz >= 5*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \ 414 *mcdst++ = *mcsrc++; \ 415 if(mcsz >= 7*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \ 416 *mcdst++ = *mcsrc++; \ 417 if(mcsz >= 9*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \ 418 *mcdst++ = *mcsrc++; }}} \ 419 *mcdst++ = *mcsrc++; \ 420 *mcdst++ = *mcsrc++; \ 421 *mcdst = *mcsrc ; \ 422 } else memcpy(dest, src, mcsz); \ 423} while(0) 424 425#else /* !USE_MEMCPY */ 426 427/* Use Duff's device for good zeroing/copying performance. */ 428 429#define MALLOC_ZERO(charp, nbytes) \ 430do { \ 431 INTERNAL_SIZE_T* mzp = (INTERNAL_SIZE_T*)(charp); \ 432 long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \ 433 if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \ 434 switch (mctmp) { \ 435 case 0: for(;;) { *mzp++ = 0; \ 436 case 7: *mzp++ = 0; \ 437 case 6: *mzp++ = 0; \ 438 case 5: *mzp++ = 0; \ 439 case 4: *mzp++ = 0; \ 440 case 3: *mzp++ = 0; \ 441 case 2: *mzp++ = 0; \ 442 case 1: *mzp++ = 0; if(mcn <= 0) break; mcn--; } \ 443 } \ 444} while(0) 445 446#define MALLOC_COPY(dest,src,nbytes) \ 447do { \ 448 INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) src; \ 449 INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) dest; \ 450 long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \ 451 if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \ 452 switch (mctmp) { \ 453 case 0: for(;;) { *mcdst++ = *mcsrc++; \ 454 case 7: *mcdst++ = *mcsrc++; \ 455 case 6: *mcdst++ = *mcsrc++; \ 456 case 5: *mcdst++ = *mcsrc++; \ 457 case 4: *mcdst++ = *mcsrc++; \ 458 case 3: *mcdst++ = *mcsrc++; \ 459 case 2: *mcdst++ = *mcsrc++; \ 460 case 1: *mcdst++ = *mcsrc++; if(mcn <= 0) break; mcn--; } \ 461 } \ 462} while(0) 463 464#endif 465 466 467/* 468 Define HAVE_MMAP to optionally make malloc() use mmap() to 469 allocate very large blocks. These will be returned to the 470 operating system immediately after a free(). 471*/ 472 473/*** 474#ifndef HAVE_MMAP 475#define HAVE_MMAP 1 476#endif 477***/ 478#undef HAVE_MMAP /* Not available for U-Boot */ 479 480/* 481 Define HAVE_MREMAP to make realloc() use mremap() to re-allocate 482 large blocks. This is currently only possible on Linux with 483 kernel versions newer than 1.3.77. 484*/ 485 486/*** 487#ifndef HAVE_MREMAP 488#ifdef INTERNAL_LINUX_C_LIB 489#define HAVE_MREMAP 1 490#else 491#define HAVE_MREMAP 0 492#endif 493#endif 494***/ 495#undef HAVE_MREMAP /* Not available for U-Boot */ 496 497#if HAVE_MMAP 498 499#include <unistd.h> 500#include <fcntl.h> 501#include <sys/mman.h> 502 503#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON) 504#define MAP_ANONYMOUS MAP_ANON 505#endif 506 507#endif /* HAVE_MMAP */ 508 509/* 510 Access to system page size. To the extent possible, this malloc 511 manages memory from the system in page-size units. 512 513 The following mechanics for getpagesize were adapted from 514 bsd/gnu getpagesize.h 515*/ 516 517#define LACKS_UNISTD_H /* Shortcut for U-Boot */ 518#define malloc_getpagesize 4096 519 520#ifndef LACKS_UNISTD_H 521# include <unistd.h> 522#endif 523 524#ifndef malloc_getpagesize 525# ifdef _SC_PAGESIZE /* some SVR4 systems omit an underscore */ 526# ifndef _SC_PAGE_SIZE 527# define _SC_PAGE_SIZE _SC_PAGESIZE 528# endif 529# endif 530# ifdef _SC_PAGE_SIZE 531# define malloc_getpagesize sysconf(_SC_PAGE_SIZE) 532# else 533# if defined(BSD) || defined(DGUX) || defined(HAVE_GETPAGESIZE) 534 extern size_t getpagesize(); 535# define malloc_getpagesize getpagesize() 536# else 537# ifdef WIN32 538# define malloc_getpagesize (4096) /* TBD: Use 'GetSystemInfo' instead */ 539# else 540# ifndef LACKS_SYS_PARAM_H 541# include <sys/param.h> 542# endif 543# ifdef EXEC_PAGESIZE 544# define malloc_getpagesize EXEC_PAGESIZE 545# else 546# ifdef NBPG 547# ifndef CLSIZE 548# define malloc_getpagesize NBPG 549# else 550# define malloc_getpagesize (NBPG * CLSIZE) 551# endif 552# else 553# ifdef NBPC 554# define malloc_getpagesize NBPC 555# else 556# ifdef PAGESIZE 557# define malloc_getpagesize PAGESIZE 558# else 559# define malloc_getpagesize (4096) /* just guess */ 560# endif 561# endif 562# endif 563# endif 564# endif 565# endif 566# endif 567#endif 568 569 570/* 571 572 This version of malloc supports the standard SVID/XPG mallinfo 573 routine that returns a struct containing the same kind of 574 information you can get from malloc_stats. It should work on 575 any SVID/XPG compliant system that has a /usr/include/malloc.h 576 defining struct mallinfo. (If you'd like to install such a thing 577 yourself, cut out the preliminary declarations as described above 578 and below and save them in a malloc.h file. But there's no 579 compelling reason to bother to do this.) 580 581 The main declaration needed is the mallinfo struct that is returned 582 (by-copy) by mallinfo(). The SVID/XPG malloinfo struct contains a 583 bunch of fields, most of which are not even meaningful in this 584 version of malloc. Some of these fields are are instead filled by 585 mallinfo() with other numbers that might possibly be of interest. 586 587 HAVE_USR_INCLUDE_MALLOC_H should be set if you have a 588 /usr/include/malloc.h file that includes a declaration of struct 589 mallinfo. If so, it is included; else an SVID2/XPG2 compliant 590 version is declared below. These must be precisely the same for 591 mallinfo() to work. 592 593*/ 594 595/* #define HAVE_USR_INCLUDE_MALLOC_H */ 596 597#if HAVE_USR_INCLUDE_MALLOC_H 598#include "/usr/include/malloc.h" 599#else 600 601/* SVID2/XPG mallinfo structure */ 602 603struct mallinfo { 604 int arena; /* total space allocated from system */ 605 int ordblks; /* number of non-inuse chunks */ 606 int smblks; /* unused -- always zero */ 607 int hblks; /* number of mmapped regions */ 608 int hblkhd; /* total space in mmapped regions */ 609 int usmblks; /* unused -- always zero */ 610 int fsmblks; /* unused -- always zero */ 611 int uordblks; /* total allocated space */ 612 int fordblks; /* total non-inuse space */ 613 int keepcost; /* top-most, releasable (via malloc_trim) space */ 614}; 615 616/* SVID2/XPG mallopt options */ 617 618#define M_MXFAST 1 /* UNUSED in this malloc */ 619#define M_NLBLKS 2 /* UNUSED in this malloc */ 620#define M_GRAIN 3 /* UNUSED in this malloc */ 621#define M_KEEP 4 /* UNUSED in this malloc */ 622 623#endif 624 625/* mallopt options that actually do something */ 626 627#define M_TRIM_THRESHOLD -1 628#define M_TOP_PAD -2 629#define M_MMAP_THRESHOLD -3 630#define M_MMAP_MAX -4 631 632 633#ifndef DEFAULT_TRIM_THRESHOLD 634#define DEFAULT_TRIM_THRESHOLD (128 * 1024) 635#endif 636 637/* 638 M_TRIM_THRESHOLD is the maximum amount of unused top-most memory 639 to keep before releasing via malloc_trim in free(). 640 641 Automatic trimming is mainly useful in long-lived programs. 642 Because trimming via sbrk can be slow on some systems, and can 643 sometimes be wasteful (in cases where programs immediately 644 afterward allocate more large chunks) the value should be high 645 enough so that your overall system performance would improve by 646 releasing. 647 648 The trim threshold and the mmap control parameters (see below) 649 can be traded off with one another. Trimming and mmapping are 650 two different ways of releasing unused memory back to the 651 system. Between these two, it is often possible to keep 652 system-level demands of a long-lived program down to a bare 653 minimum. For example, in one test suite of sessions measuring 654 the XF86 X server on Linux, using a trim threshold of 128K and a 655 mmap threshold of 192K led to near-minimal long term resource 656 consumption. 657 658 If you are using this malloc in a long-lived program, it should 659 pay to experiment with these values. As a rough guide, you 660 might set to a value close to the average size of a process 661 (program) running on your system. Releasing this much memory 662 would allow such a process to run in memory. Generally, it's 663 worth it to tune for trimming rather tham memory mapping when a 664 program undergoes phases where several large chunks are 665 allocated and released in ways that can reuse each other's 666 storage, perhaps mixed with phases where there are no such 667 chunks at all. And in well-behaved long-lived programs, 668 controlling release of large blocks via trimming versus mapping 669 is usually faster. 670 671 However, in most programs, these parameters serve mainly as 672 protection against the system-level effects of carrying around 673 massive amounts of unneeded memory. Since frequent calls to 674 sbrk, mmap, and munmap otherwise degrade performance, the default 675 parameters are set to relatively high values that serve only as 676 safeguards. 677 678 The default trim value is high enough to cause trimming only in 679 fairly extreme (by current memory consumption standards) cases. 680 It must be greater than page size to have any useful effect. To 681 disable trimming completely, you can set to (unsigned long)(-1); 682 683 684*/ 685 686 687#ifndef DEFAULT_TOP_PAD 688#define DEFAULT_TOP_PAD (0) 689#endif 690 691/* 692 M_TOP_PAD is the amount of extra `padding' space to allocate or 693 retain whenever sbrk is called. It is used in two ways internally: 694 695 * When sbrk is called to extend the top of the arena to satisfy 696 a new malloc request, this much padding is added to the sbrk 697 request. 698 699 * When malloc_trim is called automatically from free(), 700 it is used as the `pad' argument. 701 702 In both cases, the actual amount of padding is rounded 703 so that the end of the arena is always a system page boundary. 704 705 The main reason for using padding is to avoid calling sbrk so 706 often. Having even a small pad greatly reduces the likelihood 707 that nearly every malloc request during program start-up (or 708 after trimming) will invoke sbrk, which needlessly wastes 709 time. 710 711 Automatic rounding-up to page-size units is normally sufficient 712 to avoid measurable overhead, so the default is 0. However, in 713 systems where sbrk is relatively slow, it can pay to increase 714 this value, at the expense of carrying around more memory than 715 the program needs. 716 717*/ 718 719 720#ifndef DEFAULT_MMAP_THRESHOLD 721#define DEFAULT_MMAP_THRESHOLD (128 * 1024) 722#endif 723 724/* 725 726 M_MMAP_THRESHOLD is the request size threshold for using mmap() 727 to service a request. Requests of at least this size that cannot 728 be allocated using already-existing space will be serviced via mmap. 729 (If enough normal freed space already exists it is used instead.) 730 731 Using mmap segregates relatively large chunks of memory so that 732 they can be individually obtained and released from the host 733 system. A request serviced through mmap is never reused by any 734 other request (at least not directly; the system may just so 735 happen to remap successive requests to the same locations). 736 737 Segregating space in this way has the benefit that mmapped space 738 can ALWAYS be individually released back to the system, which 739 helps keep the system level memory demands of a long-lived 740 program low. Mapped memory can never become `locked' between 741 other chunks, as can happen with normally allocated chunks, which 742 menas that even trimming via malloc_trim would not release them. 743 744 However, it has the disadvantages that: 745 746 1. The space cannot be reclaimed, consolidated, and then 747 used to service later requests, as happens with normal chunks. 748 2. It can lead to more wastage because of mmap page alignment 749 requirements 750 3. It causes malloc performance to be more dependent on host 751 system memory management support routines which may vary in 752 implementation quality and may impose arbitrary 753 limitations. Generally, servicing a request via normal 754 malloc steps is faster than going through a system's mmap. 755 756 All together, these considerations should lead you to use mmap 757 only for relatively large requests. 758 759 760*/ 761 762 763#ifndef DEFAULT_MMAP_MAX 764#if HAVE_MMAP 765#define DEFAULT_MMAP_MAX (64) 766#else 767#define DEFAULT_MMAP_MAX (0) 768#endif 769#endif 770 771/* 772 M_MMAP_MAX is the maximum number of requests to simultaneously 773 service using mmap. This parameter exists because: 774 775 1. Some systems have a limited number of internal tables for 776 use by mmap. 777 2. In most systems, overreliance on mmap can degrade overall 778 performance. 779 3. If a program allocates many large regions, it is probably 780 better off using normal sbrk-based allocation routines that 781 can reclaim and reallocate normal heap memory. Using a 782 small value allows transition into this mode after the 783 first few allocations. 784 785 Setting to 0 disables all use of mmap. If HAVE_MMAP is not set, 786 the default value is 0, and attempts to set it to non-zero values 787 in mallopt will fail. 788*/ 789 790 791/* 792 USE_DL_PREFIX will prefix all public routines with the string 'dl'. 793 Useful to quickly avoid procedure declaration conflicts and linker 794 symbol conflicts with existing memory allocation routines. 795 796*/ 797 798/* #define USE_DL_PREFIX */ 799 800 801/* 802 803 Special defines for linux libc 804 805 Except when compiled using these special defines for Linux libc 806 using weak aliases, this malloc is NOT designed to work in 807 multithreaded applications. No semaphores or other concurrency 808 control are provided to ensure that multiple malloc or free calls 809 don't run at the same time, which could be disasterous. A single 810 semaphore could be used across malloc, realloc, and free (which is 811 essentially the effect of the linux weak alias approach). It would 812 be hard to obtain finer granularity. 813 814*/ 815 816 817#ifdef INTERNAL_LINUX_C_LIB 818 819#if __STD_C 820 821Void_t * __default_morecore_init (ptrdiff_t); 822Void_t *(*__morecore)(ptrdiff_t) = __default_morecore_init; 823 824#else 825 826Void_t * __default_morecore_init (); 827Void_t *(*__morecore)() = __default_morecore_init; 828 829#endif 830 831#define MORECORE (*__morecore) 832#define MORECORE_FAILURE 0 833#define MORECORE_CLEARS 1 834 835#else /* INTERNAL_LINUX_C_LIB */ 836 837#if __STD_C 838extern Void_t* sbrk(ptrdiff_t); 839#else 840extern Void_t* sbrk(); 841#endif 842 843#ifndef MORECORE 844#define MORECORE sbrk 845#endif 846 847#ifndef MORECORE_FAILURE 848#define MORECORE_FAILURE -1 849#endif 850 851#ifndef MORECORE_CLEARS 852#define MORECORE_CLEARS 1 853#endif 854 855#endif /* INTERNAL_LINUX_C_LIB */ 856 857#if defined(INTERNAL_LINUX_C_LIB) && defined(__ELF__) 858 859#define cALLOc __libc_calloc 860#define fREe __libc_free 861#define mALLOc __libc_malloc 862#define mEMALIGn __libc_memalign 863#define rEALLOc __libc_realloc 864#define vALLOc __libc_valloc 865#define pvALLOc __libc_pvalloc 866#define mALLINFo __libc_mallinfo 867#define mALLOPt __libc_mallopt 868 869#pragma weak calloc = __libc_calloc 870#pragma weak free = __libc_free 871#pragma weak cfree = __libc_free 872#pragma weak malloc = __libc_malloc 873#pragma weak memalign = __libc_memalign 874#pragma weak realloc = __libc_realloc 875#pragma weak valloc = __libc_valloc 876#pragma weak pvalloc = __libc_pvalloc 877#pragma weak mallinfo = __libc_mallinfo 878#pragma weak mallopt = __libc_mallopt 879 880#else 881 882#ifdef USE_DL_PREFIX 883#define cALLOc dlcalloc 884#define fREe dlfree 885#define mALLOc dlmalloc 886#define mEMALIGn dlmemalign 887#define rEALLOc dlrealloc 888#define vALLOc dlvalloc 889#define pvALLOc dlpvalloc 890#define mALLINFo dlmallinfo 891#define mALLOPt dlmallopt 892#else /* USE_DL_PREFIX */ 893#define cALLOc calloc 894#define fREe free 895#define mALLOc malloc 896#define mEMALIGn memalign 897#define rEALLOc realloc 898#define vALLOc valloc 899#define pvALLOc pvalloc 900#define mALLINFo mallinfo 901#define mALLOPt mallopt 902#endif /* USE_DL_PREFIX */ 903 904#endif 905 906/* Public routines */ 907 908#if __STD_C 909 910Void_t* mALLOc(size_t); 911void fREe(Void_t*); 912Void_t* rEALLOc(Void_t*, size_t); 913Void_t* mEMALIGn(size_t, size_t); 914Void_t* vALLOc(size_t); 915Void_t* pvALLOc(size_t); 916Void_t* cALLOc(size_t, size_t); 917void cfree(Void_t*); 918int malloc_trim(size_t); 919size_t malloc_usable_size(Void_t*); 920void malloc_stats(void); 921int mALLOPt(int, int); 922struct mallinfo mALLINFo(void); 923#else 924Void_t* mALLOc(); 925void fREe(); 926Void_t* rEALLOc(); 927Void_t* mEMALIGn(); 928Void_t* vALLOc(); 929Void_t* pvALLOc(); 930Void_t* cALLOc(); 931void cfree(); 932int malloc_trim(); 933size_t malloc_usable_size(); 934void malloc_stats(); 935int mALLOPt(); 936struct mallinfo mALLINFo(); 937#endif 938 939 940#ifdef __cplusplus 941}; /* end of extern "C" */ 942#endif 943