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#ifndef __MALLOC_H__ 220#define __MALLOC_H__ 221 222/* Preliminaries */ 223 224#ifndef __STD_C 225#ifdef __STDC__ 226#define __STD_C 1 227#else 228#if __cplusplus 229#define __STD_C 1 230#else 231#define __STD_C 0 232#endif /*__cplusplus*/ 233#endif /*__STDC__*/ 234#endif /*__STD_C*/ 235 236#ifndef Void_t 237#if (__STD_C || defined(WIN32)) 238#define Void_t void 239#else 240#define Void_t char 241#endif 242#endif /*Void_t*/ 243 244#if __STD_C 245#include <linux/stddef.h> /* for size_t */ 246#else 247#include <sys/types.h> 248#endif /* __STD_C */ 249 250#ifdef __cplusplus 251extern "C" { 252#endif 253 254#if 0 /* not for U-Boot */ 255#include <stdio.h> /* needed for malloc_stats */ 256#endif 257 258 259/* 260 Compile-time options 261*/ 262 263 264/* 265 Debugging: 266 267 Because freed chunks may be overwritten with link fields, this 268 malloc will often die when freed memory is overwritten by user 269 programs. This can be very effective (albeit in an annoying way) 270 in helping track down dangling pointers. 271 272 If you compile with -DDEBUG, a number of assertion checks are 273 enabled that will catch more memory errors. You probably won't be 274 able to make much sense of the actual assertion errors, but they 275 should help you locate incorrectly overwritten memory. The 276 checking is fairly extensive, and will slow down execution 277 noticeably. Calling malloc_stats or mallinfo with DEBUG set will 278 attempt to check every non-mmapped allocated and free chunk in the 279 course of computing the summmaries. (By nature, mmapped regions 280 cannot be checked very much automatically.) 281 282 Setting DEBUG may also be helpful if you are trying to modify 283 this code. The assertions in the check routines spell out in more 284 detail the assumptions and invariants underlying the algorithms. 285 286*/ 287 288#ifdef DEBUG 289/* #include <assert.h> */ 290#define assert(x) ((void)0) 291#else 292#define assert(x) ((void)0) 293#endif 294 295 296/* 297 INTERNAL_SIZE_T is the word-size used for internal bookkeeping 298 of chunk sizes. On a 64-bit machine, you can reduce malloc 299 overhead by defining INTERNAL_SIZE_T to be a 32 bit `unsigned int' 300 at the expense of not being able to handle requests greater than 301 2^31. This limitation is hardly ever a concern; you are encouraged 302 to set this. However, the default version is the same as size_t. 303*/ 304 305#ifndef INTERNAL_SIZE_T 306#define INTERNAL_SIZE_T size_t 307#endif 308 309/* 310 REALLOC_ZERO_BYTES_FREES should be set if a call to 311 realloc with zero bytes should be the same as a call to free. 312 Some people think it should. Otherwise, since this malloc 313 returns a unique pointer for malloc(0), so does realloc(p, 0). 314*/ 315 316 317/* #define REALLOC_ZERO_BYTES_FREES */ 318 319 320/* 321 WIN32 causes an emulation of sbrk to be compiled in 322 mmap-based options are not currently supported in WIN32. 323*/ 324 325/* #define WIN32 */ 326#ifdef WIN32 327#define MORECORE wsbrk 328#define HAVE_MMAP 0 329 330#define LACKS_UNISTD_H 331#define LACKS_SYS_PARAM_H 332 333/* 334 Include 'windows.h' to get the necessary declarations for the 335 Microsoft Visual C++ data structures and routines used in the 'sbrk' 336 emulation. 337 338 Define WIN32_LEAN_AND_MEAN so that only the essential Microsoft 339 Visual C++ header files are included. 340*/ 341#define WIN32_LEAN_AND_MEAN 342#include <windows.h> 343#endif 344 345 346/* 347 HAVE_MEMCPY should be defined if you are not otherwise using 348 ANSI STD C, but still have memcpy and memset in your C library 349 and want to use them in calloc and realloc. Otherwise simple 350 macro versions are defined here. 351 352 USE_MEMCPY should be defined as 1 if you actually want to 353 have memset and memcpy called. People report that the macro 354 versions are often enough faster than libc versions on many 355 systems that it is better to use them. 356 357*/ 358 359#define HAVE_MEMCPY 360 361#ifndef USE_MEMCPY 362#ifdef HAVE_MEMCPY 363#define USE_MEMCPY 1 364#else 365#define USE_MEMCPY 0 366#endif 367#endif 368 369#if (__STD_C || defined(HAVE_MEMCPY)) 370 371#if __STD_C 372void* memset(void*, int, size_t); 373void* memcpy(void*, const void*, size_t); 374#else 375#ifdef WIN32 376/* On Win32 platforms, 'memset()' and 'memcpy()' are already declared in */ 377/* 'windows.h' */ 378#else 379Void_t* memset(); 380Void_t* memcpy(); 381#endif 382#endif 383#endif 384 385#if USE_MEMCPY 386 387/* The following macros are only invoked with (2n+1)-multiples of 388 INTERNAL_SIZE_T units, with a positive integer n. This is exploited 389 for fast inline execution when n is small. */ 390 391#define MALLOC_ZERO(charp, nbytes) \ 392do { \ 393 INTERNAL_SIZE_T mzsz = (nbytes); \ 394 if(mzsz <= 9*sizeof(mzsz)) { \ 395 INTERNAL_SIZE_T* mz = (INTERNAL_SIZE_T*) (charp); \ 396 if(mzsz >= 5*sizeof(mzsz)) { *mz++ = 0; \ 397 *mz++ = 0; \ 398 if(mzsz >= 7*sizeof(mzsz)) { *mz++ = 0; \ 399 *mz++ = 0; \ 400 if(mzsz >= 9*sizeof(mzsz)) { *mz++ = 0; \ 401 *mz++ = 0; }}} \ 402 *mz++ = 0; \ 403 *mz++ = 0; \ 404 *mz = 0; \ 405 } else memset((charp), 0, mzsz); \ 406} while(0) 407 408#define MALLOC_COPY(dest,src,nbytes) \ 409do { \ 410 INTERNAL_SIZE_T mcsz = (nbytes); \ 411 if(mcsz <= 9*sizeof(mcsz)) { \ 412 INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) (src); \ 413 INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) (dest); \ 414 if(mcsz >= 5*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \ 415 *mcdst++ = *mcsrc++; \ 416 if(mcsz >= 7*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \ 417 *mcdst++ = *mcsrc++; \ 418 if(mcsz >= 9*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \ 419 *mcdst++ = *mcsrc++; }}} \ 420 *mcdst++ = *mcsrc++; \ 421 *mcdst++ = *mcsrc++; \ 422 *mcdst = *mcsrc ; \ 423 } else memcpy(dest, src, mcsz); \ 424} while(0) 425 426#else /* !USE_MEMCPY */ 427 428/* Use Duff's device for good zeroing/copying performance. */ 429 430#define MALLOC_ZERO(charp, nbytes) \ 431do { \ 432 INTERNAL_SIZE_T* mzp = (INTERNAL_SIZE_T*)(charp); \ 433 long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \ 434 if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \ 435 switch (mctmp) { \ 436 case 0: for(;;) { *mzp++ = 0; \ 437 case 7: *mzp++ = 0; \ 438 case 6: *mzp++ = 0; \ 439 case 5: *mzp++ = 0; \ 440 case 4: *mzp++ = 0; \ 441 case 3: *mzp++ = 0; \ 442 case 2: *mzp++ = 0; \ 443 case 1: *mzp++ = 0; if(mcn <= 0) break; mcn--; } \ 444 } \ 445} while(0) 446 447#define MALLOC_COPY(dest,src,nbytes) \ 448do { \ 449 INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) src; \ 450 INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) dest; \ 451 long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \ 452 if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \ 453 switch (mctmp) { \ 454 case 0: for(;;) { *mcdst++ = *mcsrc++; \ 455 case 7: *mcdst++ = *mcsrc++; \ 456 case 6: *mcdst++ = *mcsrc++; \ 457 case 5: *mcdst++ = *mcsrc++; \ 458 case 4: *mcdst++ = *mcsrc++; \ 459 case 3: *mcdst++ = *mcsrc++; \ 460 case 2: *mcdst++ = *mcsrc++; \ 461 case 1: *mcdst++ = *mcsrc++; if(mcn <= 0) break; mcn--; } \ 462 } \ 463} while(0) 464 465#endif 466 467 468/* 469 Define HAVE_MMAP to optionally make malloc() use mmap() to 470 allocate very large blocks. These will be returned to the 471 operating system immediately after a free(). 472*/ 473 474/*** 475#ifndef HAVE_MMAP 476#define HAVE_MMAP 1 477#endif 478***/ 479#undef HAVE_MMAP /* Not available for U-Boot */ 480 481/* 482 Define HAVE_MREMAP to make realloc() use mremap() to re-allocate 483 large blocks. This is currently only possible on Linux with 484 kernel versions newer than 1.3.77. 485*/ 486 487/*** 488#ifndef HAVE_MREMAP 489#ifdef INTERNAL_LINUX_C_LIB 490#define HAVE_MREMAP 1 491#else 492#define HAVE_MREMAP 0 493#endif 494#endif 495***/ 496#undef HAVE_MREMAP /* Not available for U-Boot */ 497 498#if HAVE_MMAP 499 500#include <unistd.h> 501#include <fcntl.h> 502#include <sys/mman.h> 503 504#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON) 505#define MAP_ANONYMOUS MAP_ANON 506#endif 507 508#endif /* HAVE_MMAP */ 509 510/* 511 Access to system page size. To the extent possible, this malloc 512 manages memory from the system in page-size units. 513 514 The following mechanics for getpagesize were adapted from 515 bsd/gnu getpagesize.h 516*/ 517 518#define LACKS_UNISTD_H /* Shortcut for U-Boot */ 519#define malloc_getpagesize 4096 520 521#ifndef LACKS_UNISTD_H 522# include <unistd.h> 523#endif 524 525#ifndef malloc_getpagesize 526# ifdef _SC_PAGESIZE /* some SVR4 systems omit an underscore */ 527# ifndef _SC_PAGE_SIZE 528# define _SC_PAGE_SIZE _SC_PAGESIZE 529# endif 530# endif 531# ifdef _SC_PAGE_SIZE 532# define malloc_getpagesize sysconf(_SC_PAGE_SIZE) 533# else 534# if defined(BSD) || defined(DGUX) || defined(HAVE_GETPAGESIZE) 535 extern size_t getpagesize(); 536# define malloc_getpagesize getpagesize() 537# else 538# ifdef WIN32 539# define malloc_getpagesize (4096) /* TBD: Use 'GetSystemInfo' instead */ 540# else 541# ifndef LACKS_SYS_PARAM_H 542# include <sys/param.h> 543# endif 544# ifdef EXEC_PAGESIZE 545# define malloc_getpagesize EXEC_PAGESIZE 546# else 547# ifdef NBPG 548# ifndef CLSIZE 549# define malloc_getpagesize NBPG 550# else 551# define malloc_getpagesize (NBPG * CLSIZE) 552# endif 553# else 554# ifdef NBPC 555# define malloc_getpagesize NBPC 556# else 557# ifdef PAGESIZE 558# define malloc_getpagesize PAGESIZE 559# else 560# define malloc_getpagesize (4096) /* just guess */ 561# endif 562# endif 563# endif 564# endif 565# endif 566# endif 567# endif 568#endif 569 570 571/* 572 573 This version of malloc supports the standard SVID/XPG mallinfo 574 routine that returns a struct containing the same kind of 575 information you can get from malloc_stats. It should work on 576 any SVID/XPG compliant system that has a /usr/include/malloc.h 577 defining struct mallinfo. (If you'd like to install such a thing 578 yourself, cut out the preliminary declarations as described above 579 and below and save them in a malloc.h file. But there's no 580 compelling reason to bother to do this.) 581 582 The main declaration needed is the mallinfo struct that is returned 583 (by-copy) by mallinfo(). The SVID/XPG malloinfo struct contains a 584 bunch of fields, most of which are not even meaningful in this 585 version of malloc. Some of these fields are are instead filled by 586 mallinfo() with other numbers that might possibly be of interest. 587 588 HAVE_USR_INCLUDE_MALLOC_H should be set if you have a 589 /usr/include/malloc.h file that includes a declaration of struct 590 mallinfo. If so, it is included; else an SVID2/XPG2 compliant 591 version is declared below. These must be precisely the same for 592 mallinfo() to work. 593 594*/ 595 596/* #define HAVE_USR_INCLUDE_MALLOC_H */ 597 598#if HAVE_USR_INCLUDE_MALLOC_H 599#include "/usr/include/malloc.h" 600#else 601 602/* SVID2/XPG mallinfo structure */ 603 604struct mallinfo { 605 int arena; /* total space allocated from system */ 606 int ordblks; /* number of non-inuse chunks */ 607 int smblks; /* unused -- always zero */ 608 int hblks; /* number of mmapped regions */ 609 int hblkhd; /* total space in mmapped regions */ 610 int usmblks; /* unused -- always zero */ 611 int fsmblks; /* unused -- always zero */ 612 int uordblks; /* total allocated space */ 613 int fordblks; /* total non-inuse space */ 614 int keepcost; /* top-most, releasable (via malloc_trim) space */ 615}; 616 617/* SVID2/XPG mallopt options */ 618 619#define M_MXFAST 1 /* UNUSED in this malloc */ 620#define M_NLBLKS 2 /* UNUSED in this malloc */ 621#define M_GRAIN 3 /* UNUSED in this malloc */ 622#define M_KEEP 4 /* UNUSED in this malloc */ 623 624#endif 625 626/* mallopt options that actually do something */ 627 628#define M_TRIM_THRESHOLD -1 629#define M_TOP_PAD -2 630#define M_MMAP_THRESHOLD -3 631#define M_MMAP_MAX -4 632 633 634#ifndef DEFAULT_TRIM_THRESHOLD 635#define DEFAULT_TRIM_THRESHOLD (128 * 1024) 636#endif 637 638/* 639 M_TRIM_THRESHOLD is the maximum amount of unused top-most memory 640 to keep before releasing via malloc_trim in free(). 641 642 Automatic trimming is mainly useful in long-lived programs. 643 Because trimming via sbrk can be slow on some systems, and can 644 sometimes be wasteful (in cases where programs immediately 645 afterward allocate more large chunks) the value should be high 646 enough so that your overall system performance would improve by 647 releasing. 648 649 The trim threshold and the mmap control parameters (see below) 650 can be traded off with one another. Trimming and mmapping are 651 two different ways of releasing unused memory back to the 652 system. Between these two, it is often possible to keep 653 system-level demands of a long-lived program down to a bare 654 minimum. For example, in one test suite of sessions measuring 655 the XF86 X server on Linux, using a trim threshold of 128K and a 656 mmap threshold of 192K led to near-minimal long term resource 657 consumption. 658 659 If you are using this malloc in a long-lived program, it should 660 pay to experiment with these values. As a rough guide, you 661 might set to a value close to the average size of a process 662 (program) running on your system. Releasing this much memory 663 would allow such a process to run in memory. Generally, it's 664 worth it to tune for trimming rather tham memory mapping when a 665 program undergoes phases where several large chunks are 666 allocated and released in ways that can reuse each other's 667 storage, perhaps mixed with phases where there are no such 668 chunks at all. And in well-behaved long-lived programs, 669 controlling release of large blocks via trimming versus mapping 670 is usually faster. 671 672 However, in most programs, these parameters serve mainly as 673 protection against the system-level effects of carrying around 674 massive amounts of unneeded memory. Since frequent calls to 675 sbrk, mmap, and munmap otherwise degrade performance, the default 676 parameters are set to relatively high values that serve only as 677 safeguards. 678 679 The default trim value is high enough to cause trimming only in 680 fairly extreme (by current memory consumption standards) cases. 681 It must be greater than page size to have any useful effect. To 682 disable trimming completely, you can set to (unsigned long)(-1); 683 684 685*/ 686 687 688#ifndef DEFAULT_TOP_PAD 689#define DEFAULT_TOP_PAD (0) 690#endif 691 692/* 693 M_TOP_PAD is the amount of extra `padding' space to allocate or 694 retain whenever sbrk is called. It is used in two ways internally: 695 696 * When sbrk is called to extend the top of the arena to satisfy 697 a new malloc request, this much padding is added to the sbrk 698 request. 699 700 * When malloc_trim is called automatically from free(), 701 it is used as the `pad' argument. 702 703 In both cases, the actual amount of padding is rounded 704 so that the end of the arena is always a system page boundary. 705 706 The main reason for using padding is to avoid calling sbrk so 707 often. Having even a small pad greatly reduces the likelihood 708 that nearly every malloc request during program start-up (or 709 after trimming) will invoke sbrk, which needlessly wastes 710 time. 711 712 Automatic rounding-up to page-size units is normally sufficient 713 to avoid measurable overhead, so the default is 0. However, in 714 systems where sbrk is relatively slow, it can pay to increase 715 this value, at the expense of carrying around more memory than 716 the program needs. 717 718*/ 719 720 721#ifndef DEFAULT_MMAP_THRESHOLD 722#define DEFAULT_MMAP_THRESHOLD (128 * 1024) 723#endif 724 725/* 726 727 M_MMAP_THRESHOLD is the request size threshold for using mmap() 728 to service a request. Requests of at least this size that cannot 729 be allocated using already-existing space will be serviced via mmap. 730 (If enough normal freed space already exists it is used instead.) 731 732 Using mmap segregates relatively large chunks of memory so that 733 they can be individually obtained and released from the host 734 system. A request serviced through mmap is never reused by any 735 other request (at least not directly; the system may just so 736 happen to remap successive requests to the same locations). 737 738 Segregating space in this way has the benefit that mmapped space 739 can ALWAYS be individually released back to the system, which 740 helps keep the system level memory demands of a long-lived 741 program low. Mapped memory can never become `locked' between 742 other chunks, as can happen with normally allocated chunks, which 743 menas that even trimming via malloc_trim would not release them. 744 745 However, it has the disadvantages that: 746 747 1. The space cannot be reclaimed, consolidated, and then 748 used to service later requests, as happens with normal chunks. 749 2. It can lead to more wastage because of mmap page alignment 750 requirements 751 3. It causes malloc performance to be more dependent on host 752 system memory management support routines which may vary in 753 implementation quality and may impose arbitrary 754 limitations. Generally, servicing a request via normal 755 malloc steps is faster than going through a system's mmap. 756 757 All together, these considerations should lead you to use mmap 758 only for relatively large requests. 759 760 761*/ 762 763 764#ifndef DEFAULT_MMAP_MAX 765#if HAVE_MMAP 766#define DEFAULT_MMAP_MAX (64) 767#else 768#define DEFAULT_MMAP_MAX (0) 769#endif 770#endif 771 772/* 773 M_MMAP_MAX is the maximum number of requests to simultaneously 774 service using mmap. This parameter exists because: 775 776 1. Some systems have a limited number of internal tables for 777 use by mmap. 778 2. In most systems, overreliance on mmap can degrade overall 779 performance. 780 3. If a program allocates many large regions, it is probably 781 better off using normal sbrk-based allocation routines that 782 can reclaim and reallocate normal heap memory. Using a 783 small value allows transition into this mode after the 784 first few allocations. 785 786 Setting to 0 disables all use of mmap. If HAVE_MMAP is not set, 787 the default value is 0, and attempts to set it to non-zero values 788 in mallopt will fail. 789*/ 790 791 792/* 793 USE_DL_PREFIX will prefix all public routines with the string 'dl'. 794 Useful to quickly avoid procedure declaration conflicts and linker 795 symbol conflicts with existing memory allocation routines. 796 797*/ 798 799/* #define USE_DL_PREFIX */ 800 801 802/* 803 804 Special defines for linux libc 805 806 Except when compiled using these special defines for Linux libc 807 using weak aliases, this malloc is NOT designed to work in 808 multithreaded applications. No semaphores or other concurrency 809 control are provided to ensure that multiple malloc or free calls 810 don't run at the same time, which could be disasterous. A single 811 semaphore could be used across malloc, realloc, and free (which is 812 essentially the effect of the linux weak alias approach). It would 813 be hard to obtain finer granularity. 814 815*/ 816 817 818#ifdef INTERNAL_LINUX_C_LIB 819 820#if __STD_C 821 822Void_t * __default_morecore_init (ptrdiff_t); 823Void_t *(*__morecore)(ptrdiff_t) = __default_morecore_init; 824 825#else 826 827Void_t * __default_morecore_init (); 828Void_t *(*__morecore)() = __default_morecore_init; 829 830#endif 831 832#define MORECORE (*__morecore) 833#define MORECORE_FAILURE 0 834#define MORECORE_CLEARS 1 835 836#else /* INTERNAL_LINUX_C_LIB */ 837 838#if __STD_C 839extern Void_t* sbrk(ptrdiff_t); 840#else 841extern Void_t* sbrk(); 842#endif 843 844#ifndef MORECORE 845#define MORECORE sbrk 846#endif 847 848#ifndef MORECORE_FAILURE 849#define MORECORE_FAILURE -1 850#endif 851 852#ifndef MORECORE_CLEARS 853#define MORECORE_CLEARS 1 854#endif 855 856#endif /* INTERNAL_LINUX_C_LIB */ 857 858#if defined(INTERNAL_LINUX_C_LIB) && defined(__ELF__) 859 860#define cALLOc __libc_calloc 861#define fREe __libc_free 862#define mALLOc __libc_malloc 863#define mEMALIGn __libc_memalign 864#define rEALLOc __libc_realloc 865#define vALLOc __libc_valloc 866#define pvALLOc __libc_pvalloc 867#define mALLINFo __libc_mallinfo 868#define mALLOPt __libc_mallopt 869 870#pragma weak calloc = __libc_calloc 871#pragma weak free = __libc_free 872#pragma weak cfree = __libc_free 873#pragma weak malloc = __libc_malloc 874#pragma weak memalign = __libc_memalign 875#pragma weak realloc = __libc_realloc 876#pragma weak valloc = __libc_valloc 877#pragma weak pvalloc = __libc_pvalloc 878#pragma weak mallinfo = __libc_mallinfo 879#pragma weak mallopt = __libc_mallopt 880 881#else 882 883#ifdef USE_DL_PREFIX 884#define cALLOc dlcalloc 885#define fREe dlfree 886#define mALLOc dlmalloc 887#define mEMALIGn dlmemalign 888#define rEALLOc dlrealloc 889#define vALLOc dlvalloc 890#define pvALLOc dlpvalloc 891#define mALLINFo dlmallinfo 892#define mALLOPt dlmallopt 893#else /* USE_DL_PREFIX */ 894#define cALLOc calloc 895#define fREe free 896#define mALLOc malloc 897#define mEMALIGn memalign 898#define rEALLOc realloc 899#define vALLOc valloc 900#define pvALLOc pvalloc 901#define mALLINFo mallinfo 902#define mALLOPt mallopt 903#endif /* USE_DL_PREFIX */ 904 905#endif 906 907/* Public routines */ 908 909#if __STD_C 910 911Void_t* mALLOc(size_t); 912void fREe(Void_t*); 913Void_t* rEALLOc(Void_t*, size_t); 914Void_t* mEMALIGn(size_t, size_t); 915Void_t* vALLOc(size_t); 916Void_t* pvALLOc(size_t); 917Void_t* cALLOc(size_t, size_t); 918void cfree(Void_t*); 919int malloc_trim(size_t); 920size_t malloc_usable_size(Void_t*); 921void malloc_stats(void); 922int mALLOPt(int, int); 923struct mallinfo mALLINFo(void); 924#else 925Void_t* mALLOc(); 926void fREe(); 927Void_t* rEALLOc(); 928Void_t* mEMALIGn(); 929Void_t* vALLOc(); 930Void_t* pvALLOc(); 931Void_t* cALLOc(); 932void cfree(); 933int malloc_trim(); 934size_t malloc_usable_size(); 935void malloc_stats(); 936int mALLOPt(); 937struct mallinfo mALLINFo(); 938#endif 939 940/* 941 * Begin and End of memory area for malloc(), and current "brk" 942 */ 943extern ulong mem_malloc_start; 944extern ulong mem_malloc_end; 945extern ulong mem_malloc_brk; 946 947void mem_malloc_init(ulong start, ulong size); 948 949#ifdef __cplusplus 950}; /* end of extern "C" */ 951#endif 952 953#endif /* __MALLOC_H__ */ 954