posix_madvise(3) — Linux manual page


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

NAME         top

       posix_madvise - give advice about patterns of memory usage

SYNOPSIS         top

       #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_C_SOURCE >= 200112L

DESCRIPTION         top

       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:

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

              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.

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

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

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

RETURN VALUE         top

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

ERRORS         top

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

       EINVAL advice is invalid.

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

VERSIONS         top

       Support for posix_madvise() first appeared in glibc version 2.2.

CONFORMING TO         top


NOTES         top

       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

SEE ALSO         top

       madvise(2), posix_fadvise(2)

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2017-09-15                 POSIX_MADVISE(3)

Pages that refer to this page: arm_fadvise(2)arm_fadvise64_64(2)fadvise64(2)fadvise64_64(2)madvise(2)mincore(2)posix_fadvise(2)