malloc_usable_size(void* p);  Returns the number of bytes you can actually use in an allocated  chunk, which may be more than you requested (although often not) due  to alignment and minimum size constraints.  You can use this many  bytes without worrying about overwriting other allocated  objects. This is not a particularly great programming practice. But  malloc_usable_size can be more useful in debugging and assertions,  for example:  p = malloc(n);  assert(malloc_usable_size(p) >= 256);*/#ifndef USE_DL_PREFIXsize_t   malloc_usable_size(void*);#elsesize_t   dlmalloc_usable_size(void*);#endif/*  malloc_stats();  Prints on stderr the amount of space obtained from the system (both  via sbrk and mmap), the maximum amount (which may be more than  current if malloc_trim and/or munmap got called), and the current  number of bytes allocated via malloc (or realloc, etc) but not yet  freed. Note that this is the number of bytes allocated, not the  number requested. It will be larger than the number requested  because of alignment and bookkeeping overhead. Because it includes  alignment wastage as being in use, this figure may be greater than  zero even when no user-level chunks are allocated.  The reported current and maximum system memory can be inaccurate if  a program makes other calls to system memory allocation functions  (normally sbrk) outside of malloc.  malloc_stats prints only the most commonly interesting statistics.  More information can be obtained by calling mallinfo.*/#ifndef USE_DL_PREFIXvoid     malloc_stats();#elsevoid     dlmalloc_stats();#endif/*  mallinfo()  Returns (by copy) a struct containing various summary statistics:  arena:     current total non-mmapped bytes allocated from system   ordblks:   the number of free chunks   smblks:    the number of fastbin blocks (i.e., small chunks that               have been freed but not use resused or consolidated)  hblks:     current number of mmapped regions   hblkhd:    total bytes held in mmapped regions   usmblks:   the maximum total allocated space. This will be greater                than current total if trimming has occurred.  fsmblks:   total bytes held in fastbin blocks   uordblks:  current total allocated space (normal or mmapped)  fordblks:  total free space   keepcost:  the maximum number of bytes that could ideally be released               back to system via malloc_trim. ("ideally" means that               it ignores page restrictions etc.)  The names of some of these fields don't bear much relation with  their contents because this struct was defined as standard in  SVID/XPG so reflects the malloc implementation that was then used  in SystemV Unix.    The original SVID version of this struct, defined on most systems  with mallinfo, declares all fields as ints. But some others define  as unsigned long. If your system defines the fields using a type of  different width than listed here, you should #include your system  version before including this file.  The struct declaration is  suppressed if _MALLOC_H is defined (which is done in most system  malloc.h files). You can also suppress it by defining  HAVE_USR_INCLUDE_MALLOC_H.  Because these fields are ints, but internal bookkeeping is done with  unsigned longs, the reported values may appear as negative, and may  wrap around zero and thus be inaccurate.*/#ifndef HAVE_USR_INCLUDE_MALLOC_H#ifndef _MALLOC_Hstruct mallinfo {  int arena;      int ordblks;    int smblks;     int hblks;      int hblkhd;     int usmblks;    int fsmblks;    int uordblks;   int fordblks;   int keepcost; };#endif#endif#ifndef USE_DL_PREFIXstruct mallinfo mallinfo(void);#elsestruct mallinfo mallinfo(void);#endif/*  mallopt(int parameter_number, int parameter_value)  Sets tunable parameters The format is to provide a  (parameter-number, parameter-value) pair.  mallopt then sets the  corresponding parameter to the argument value if it can (i.e., so  long as the value is meaningful), and returns 1 if successful else  0.  SVID/XPG defines four standard param numbers for mallopt,  normally defined in malloc.h.  Only one of these (M_MXFAST) is used  in this malloc. The others (M_NLBLKS, M_GRAIN, M_KEEP) don't apply,  so setting them has no effect. But this malloc also supports four  other options in mallopt. See below for details.  Briefly, supported  parameters are as follows (listed defaults are for "typical"  configurations).  Symbol            param #   default    allowed param values  M_MXFAST          1         64         0-80  (0 disables fastbins)  M_TRIM_THRESHOLD -1         128*1024   any   (-1U disables trimming)  M_TOP_PAD        -2         0          any    M_MMAP_THRESHOLD -3         128*1024   any   (or 0 if no MMAP support)  M_MMAP_MAX       -4         65536      any   (0 disables use of mmap)*/#ifndef USE_DL_PREFIXint  mallopt(int, int);#elseint  dlmallopt(int, int);#endif/* Descriptions of tuning options *//*  M_MXFAST is the maximum request size used for "fastbins", special bins  that hold returned chunks without consolidating their spaces. This  enables future requests for chunks of the same size to be handled  very quickly, but can increase fragmentation, and thus increase the  overall memory footprint of a program.  This malloc manages fastbins very conservatively yet still  efficiently, so fragmentation is rarely a problem for values less  than or equal to the default.  The maximum supported value of MXFAST  is 80. You wouldn't want it any higher than this anyway.  Fastbins  are designed especially for use with many small structs, objects or  strings -- the default handles structs/objects/arrays with sizes up  to 8 4byte fields, or small strings representing words, tokens,  etc. Using fastbins for larger objects normally worsens  fragmentation without improving speed.  You can reduce M_MXFAST to 0 to disable all use of fastbins.  This  causes the malloc algorithm to be a closer approximation of  fifo-best-fit in all cases, not just for larger requests, but will  generally cause it to be slower.*/#ifndef M_MXFAST#define M_MXFAST  1#endif/*  M_TRIM_THRESHOLD is the maximum amount of unused top-most memory  to keep before releasing via malloc_trim in free().  Automatic trimming is mainly useful in long-lived programs.  Because trimming via sbrk can be slow on some systems, and can  sometimes be wasteful (in cases where programs immediately  afterward allocate more large chunks) the value should be high  enough so that your overall system performance would improve by  releasing this much memory.  The trim threshold and the mmap control parameters (see below)  can be traded off with one another. Trimming and mmapping are  two different ways of releasing unused memory back to the  system. Between these two, it is often possible to keep  system-level demands of a long-lived program down to a bare  minimum. For example, in one test suite of sessions measuring  the XF86 X server on Linux, using a trim threshold of 128K and a  mmap threshold of 192K led to near-minimal long term resource  consumption.  If you are using this malloc in a long-lived program, it should  pay to experiment with these values.  As a rough guide, you  might set to a value close to the average size of a process  (program) running on your system.  Releasing this much memory  would allow such a process to run in memory.  Generally, it's  worth it to tune for trimming rather tham memory mapping when a  program undergoes phases where several large chunks are  allocated and released in ways that can reuse each other's  storage, perhaps mixed with phases where there are no such  chunks at all.  And in well-behaved long-lived programs,  controlling release of large blocks via trimming versus mapping  is usually faster.  However, in most programs, these parameters serve mainly as  protection against the system-level effects of carrying around  massive amounts of unneeded memory. Since frequent calls to  sbrk, mmap, and munmap otherwise degrade performance, the default  parameters are set to relatively high values that serve only as  safeguards.  The trim value It must be greater than page size to have any useful  effect.  To disable trimming completely, you can set to   (unsigned long)(-1)  Trim settings interact with fastbin (MXFAST) settings: Unless  compiled with TRIM_FASTBINS defined, automatic trimming never takes  place upon freeing a chunk with size less than or equal to  MXFAST. Trimming is instead delayed until subsequent freeing of  larger chunks. However, you can still force an attempted trim by  calling malloc_trim.  Also, trimming is not generally possible in cases where  the main arena is obtained via mmap.  Note that the trick some people use of mallocing a huge space and  then freeing it at program startup, in an attempt to reserve system  memory, doesn't have the intended effect under automatic trimming,  since that memory will immediately be returned to the system.*/#define M_TRIM_THRESHOLD    -1/*  M_TOP_PAD is the amount of extra `padding' space to allocate or  retain whenever sbrk is called. It is used in two ways internally:  * When sbrk is called to extend the top of the arena to satisfy  a new malloc request, this much padding is added to the sbrk  request.  * When malloc_trim is called automatically from free(),  it is used as the `pad' argument.  In both cases, the actual amount of padding is rounded  so that the end of the arena is always a system page boundary.  The main reason for using padding is to avoid calling sbrk so  often. Having even a small pad greatly reduces the likelihood  that nearly every malloc request during program start-up (or  after trimming) will invoke sbrk, which needlessly wastes  time.  Automatic rounding-up to page-size units is normally sufficient  to avoid measurable overhead, so the default is 0.  However, in  systems where sbrk is relatively slow, it can pay to increase  this value, at the expense of carrying around more memory than  the program needs.*/#define M_TOP_PAD           -2/*  M_MMAP_THRESHOLD is the request size threshold for using mmap()  to service a request. Requests of at least this size that cannot  be allocated using already-existing space will be serviced via mmap.  (If enough normal freed space already exists it is used instead.)  Using mmap segregates relatively large chunks of memory so that  they can be individually obtained and released from the host  system. A request serviced through mmap is never reused by any  other request (at least not directly; the system may just so  happen to remap successive requests to the same locations).  Segregating space in this way has the benefits that:   1. Mmapped space can ALWAYS be individually released back       to the system, which helps keep the system level memory       demands of a long-lived program low.    2. Mapped memory can never become `locked' between      other chunks, as can happen with normally allocated chunks, which      means that even trimming via malloc_trim would not release them.   3. On some systems with "holes" in address spaces, mmap can obtain      memory that sbrk cannot.  However, it has the disadvantages that:   1. The space cannot be reclaimed, consolidated, and then      used to service later requests, as happens with normal chunks.   2. It can lead to more wastage because of mmap page alignment      requirements   3. It causes malloc performance to be more dependent on host      system memory management support routines.  The advantages of mmap nearly always outweigh disadvantages for  "large" chunks, but the value of "large" varies across systems.  The  default is an empirically derived value that works well in most  systems.*/#define M_MMAP_THRESHOLD    -3/*  M_MMAP_MAX is the maximum number of requests to simultaneously  service using mmap. This parameter exists because  some systems have a limited number of internal tables for  use by mmap, and using more than a few of them may degrade  performance.  The default is set to a value that serves only as a safeguard.  Setting to 0 disables use of mmap for servicing large requests.  If  mmap is not supported on a system, the default value is 0, and  attempts to set it to non-zero values in mallopt will fail.*/#define M_MMAP_MAX          -4/* Unused SVID2/XPG mallopt options, listed for completeness */#ifndef M_NBLKS#define M_NLBLKS  2    /* UNUSED in this malloc */#endif#ifndef M_GRAIN#define M_GRAIN   3    /* UNUSED in this malloc */#endif#ifndef M_KEEP#define M_KEEP    4    /* UNUSED in this malloc */#endif/*   Some malloc.h's declare alloca, even though it is not part of malloc.*/#ifndef _ALLOCA_Hextern void* alloca(size_t);#endif#ifdef __cplusplus};  /* end of extern "C" */#endif#endif /* MALLOC_270_H */