man3/malloc_trim.3

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  26 .TH MALLOC_TRIM 3  2019-05-09 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 malloc_trim \- release free memory from the heap
  29 .SH SYNOPSIS
  30 .B #include <malloc.h>
  31 .PP
  32 .BI "int malloc_trim(size_t "  pad );
  33 .SH DESCRIPTION
  34 The
  35 .BR malloc_trim ()
  36 function attempts to release free memory from the heap
  37 (by calling
  38 .BR sbrk (2)
  39 or
  40 .BR madvise (2)
  41 with suitable arguments).
  42 .PP
  43 The
  44 .I pad
  45 argument specifies the amount of free space to leave untrimmed
  46 at the top of the heap.
  47 If this argument is 0, only the minimum amount of memory is maintained
  48 at the top of the heap (i.e., one page or less).
  49 A nonzero argument can be used to maintain some trailing space
  50 at the top of the heap in order to allow future allocations
  51 to be made without having to extend the heap with
  52 .BR sbrk (2).
  53 .SH RETURN VALUE
  54 The
  55 .BR malloc_trim ()
  56 function returns 1 if memory was actually released back to the system,
  57 or 0 if it was not possible to release any memory.
  58 .SH ERRORS
  59 No errors are defined.
  60 .\" .SH VERSIONS
  61 .\" Available already in glibc 2.0, possibly earlier
  62 .SH ATTRIBUTES
  63 For an explanation of the terms used in this section, see
  64 .BR attributes (7).
  65 .TS
  66 allbox;
  67 lb lb lb
  68 l l l.
  69 Interface       Attribute       Value
  70 T{
  71 .BR malloc_trim ()
  72 T}      Thread safety   MT-Safe
  73 .TE
  74 .sp 1
  75 .SH CONFORMING TO
  76 This function is a GNU extension.
  77 .SH NOTES
  78 This function is automatically called by
  79 .BR free (3)
  80 in certain circumstances; see the discussion of
  81 .B M_TOP_PAD
  82 and
  83 .B M_TRIM_THRESHOLD
  84 in
  85 .BR mallopt (3).
  86 .PP
  87 Only the main heap (using
  88 .BR sbrk (2))
  89 honors the
  90 .I pad
  91 argument; thread heaps do not.
  92 .PP
  93 Since glibc 2.8 this function frees memory in all arenas and in all
  94 chunks with whole free pages.
  95 .\" See commit 68631c8eb92ff38d9da1ae34f6aa048539b199cc
  96 .\" (dated 2007-12-16) which adds iteration over all
  97 .\" arenas and frees all pages in chunks which are free.
  98 .PP
  99 Before glibc 2.8 this function only freed memory at the
 100 top of the heap in the main arena.
 101 .SH SEE ALSO
 102 .BR sbrk (2),
 103 .BR malloc (3),
 104 .BR mallopt (3)