posix_madvise(3)

1posix_madvise(3)           Library Functions Manual           posix_madvise(3)
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NAME

6       posix_madvise - give advice about patterns of memory usage
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <sys/mman.h>
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14       int posix_madvise(void addr[.len], size_t len, int advice);
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16   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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18       posix_madvise():
19           _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

22       The posix_madvise() function allows an application to advise the system
23       about its expected patterns of usage of memory  in  the  address  range
24       starting  at  addr and continuing for len bytes.  The system is free to
25       use this advice in order to improve the performance of memory  accesses
26       (or to ignore the advice altogether), but calling posix_madvise() shall
27       not affect the semantics of access to memory in the specified range.
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29       The advice argument is one of the following:
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31       POSIX_MADV_NORMAL
32              The application has no special advice regarding its memory usage
33              patterns  for  the specified address range.  This is the default
34              behavior.
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36       POSIX_MADV_SEQUENTIAL
37              The application expects to access the  specified  address  range
38              sequentially,  running from lower addresses to higher addresses.
39              Hence, pages in this region can be aggressively read ahead,  and
40              may be freed soon after they are accessed.
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42       POSIX_MADV_RANDOM
43              The  application  expects  to access the specified address range
44              randomly.  Thus, read ahead may be less useful than normally.
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46       POSIX_MADV_WILLNEED
47              The application expects to access the specified address range in
48              the near future.  Thus, read ahead may be beneficial.
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50       POSIX_MADV_DONTNEED
51              The  application  expects  that it will not access the specified
52              address range in the near future.
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RETURN VALUE

55       On success, posix_madvise() returns 0.  On failure, it returns a  posi‐
56       tive error number.
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ERRORS

59       EINVAL addr  is  not a multiple of the system page size or len is nega‐
60              tive.
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62       EINVAL advice is invalid.
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64       ENOMEM Addresses in the specified range  are  partially  or  completely
65              outside the caller's address space.
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VERSIONS

68       POSIX.1 permits an implementation to generate an error if len is 0.  On
69       Linux, specifying len as 0 is permitted (as a successful no-op).
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71       In glibc, this function  is  implemented  using  madvise(2).   However,
72       since glibc 2.6, POSIX_MADV_DONTNEED is treated as a no-op, because the
73       corresponding madvise(2) value, MADV_DONTNEED, has  destructive  seman‐
74       tics.
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STANDARDS

77       POSIX.1-2008.
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HISTORY

80       glibc 2.2.  POSIX.1-2001.
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