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)

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