posix_madvise(3) — Linux manual page

posix_madvise(3)        Library Functions Manual        posix_madvise(3)

NAME

       posix_madvise - give advice about patterns of memory usage

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/mman.h>

       int posix_madvise(void addr[.len], size_t len, int advice);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       posix_madvise():
           _POSIX_C_SOURCE >= 200112L

DESCRIPTION

       The posix_madvise() function allows an application to advise the
       system about its expected patterns of usage of memory in the
       address range starting at addr and continuing for len bytes.  The
       system is free to use this advice in order to improve the
       performance of memory accesses (or to ignore the advice
       altogether), but calling posix_madvise() shall not affect the
       semantics of access to memory in the specified range.

       The advice argument is one of the following:

       POSIX_MADV_NORMAL
              The application has no special advice regarding its memory
              usage patterns for the specified address range.  This is
              the default behavior.

       POSIX_MADV_SEQUENTIAL
              The application expects to access the specified address
              range sequentially, running from lower addresses to higher
              addresses.  Hence, pages in this region can be
              aggressively read ahead, and may be freed soon after they
              are accessed.

       POSIX_MADV_RANDOM
              The application expects to access the specified address
              range randomly.  Thus, read ahead may be less useful than
              normally.

       POSIX_MADV_WILLNEED
              The application expects to access the specified address
              range in the near future.  Thus, read ahead may be
              beneficial.

       POSIX_MADV_DONTNEED
              The application expects that it will not access the
              specified address range in the near future.

RETURN VALUE

       On success, posix_madvise() returns 0.  On failure, it returns a
       positive error number.

ERRORS

       EINVAL addr is not a multiple of the system page size or len is
              negative.

       EINVAL advice is invalid.

       ENOMEM Addresses in the specified range are partially or
              completely outside the caller's address space.

VERSIONS

       POSIX.1 permits an implementation to generate an error if len is
       0.  On Linux, specifying len as 0 is permitted (as a successful
       no-op).

       In glibc, this function is implemented using madvise(2).
       However, since glibc 2.6, POSIX_MADV_DONTNEED is treated as a no-
       op, because the corresponding madvise(2) value, MADV_DONTNEED,
       has destructive semantics.

STANDARDS

       POSIX.1-2008.

HISTORY

       glibc 2.2.  POSIX.1-2001.

SEE ALSO

       madvise(2), posix_fadvise(2)

COLOPHON

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Linux man-pages 6.9.1          2024-05-02               posix_madvise(3)

Pages that refer to this page: madvise(2), mincore(2), posix_fadvise(2)

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