posix_madvise

POSIX_MADVISE(3)            Linux Programmer's Manual           POSIX_MADVISE(3)



NAME
       posix_madvise - give advice about patterns of memory usage

SYNOPSIS
       #include <sys/mman.h>

       int posix_madvise(void *addr, 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
       Support for posix_madvise() first appeared in glibc version 2.2.

CONFORMING TO
       POSIX.1-2001.

NOTES
       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.

SEE ALSO
       madvise(2), posix_fadvise(2)

COLOPHON
       This page is part of release 5.11 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux                              2021-03-22                   POSIX_MADVISE(3)