2015-02-03 14:43:21 +00:00
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Changes, ldd.1, chown.2, epoll_wait.2, get_mempolicy.2, ioctl_getfsmap.2, madvise.2, membarrier.2, mount.2, pipe.2, readv.2, seccomp.2, sigaltstack.2, splice.2, tee.2, timer_create.2, vmsplice.2, acosh.3, asinh.3, atanh.3, bsd_signal.3, dl_iterate_phdr.3, dlsym.3, flockfile.3, fpathconf.3, ftw.3, getaddrinfo.3, getcontext.3, getgrent.3, if_nametoindex.3, malloc.3, nl_langinfo.3, posix_madvise.3, ptsname.3, rand.3, resolver.3, sigpause.3, sigwait.3, strtol.3, sysconf.3, ttyslot.3, unlocked_stdio.3, unlockpt.3, capabilities.7, cgroup_namespaces.7, inode.7, man.7, pipe.7, sigevent.7: tstamp
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2017-07-13 05:49:18 +00:00
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.TH POSIX_MADVISE 3 2017-07-13 Linux "Linux Programmer's Manual"
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2015-02-03 14:43:21 +00:00
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.SH NAME
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posix_madvise \- give advice about patterns of memory usage
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.SH SYNOPSIS
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.nf
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.B #include <sys/mman.h>
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.BI "int posix_madvise(void *" addr ", size_t " len ", int " advice );
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.fi
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.BR posix_madvise ():
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.br
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.RS 4
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.ad l
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brk.2, chroot.2, clock_nanosleep.2, getpagesize.2, posix_fadvise.2, select.2, select_tut.2, seteuid.2, clock_getcpuclockid.3, ecvt.3, exp2.3, fseeko.3, gcvt.3, getdtablesize.3, getpass.3, getw.3, log2.3, mktemp.3, mq_receive.3, mq_send.3, posix_fallocate.3, posix_madvise.3, posix_memalign.3, pthread_attr_setstack.3, rint.3, sem_wait.3, setenv.3, sockatmark.3, strerror.3: Simplify FTM requirements
Looking at <features.h> (or feature_test_macros(7)), one can
see that when _XOPEN_SOURCE is defined with the value 600
(or greater), then _POSIX_C_SOURCE is defined with the value
200112L (or greater). Therefore, terms in the man pages such as
_XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
can be simpified to:
_POSIX_C_SOURCE\ >=\ 200112L
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2016-02-08 09:52:51 +00:00
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_POSIX_C_SOURCE >= 200112L
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2015-02-03 14:43:21 +00:00
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.RE
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.ad
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.SH DESCRIPTION
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The
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.BR posix_madvise ()
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function allows an application to advise the system about its expected
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patterns of usage of memory in the address range starting at
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.I addr
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and continuing for
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.I len
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bytes.
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The system is free to use this advice in order to improve the performance
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of memory accesses (or to ignore the advice altogether), but calling
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.BR posix_madvise ()
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shall not affect the semantics of access to memory in the specified range.
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The
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.I advice
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argument is one of the following:
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.TP
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.B POSIX_MADV_NORMAL
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The application has no special advice regarding its memory usage patterns
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for the specified address range.
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This is the default behavior.
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.TP
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.B POSIX_MADV_SEQUENTIAL
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The application expects to access the specified address range sequentially,
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running from lower addresses to higher addresses.
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Hence, pages in this region can be aggressively read ahead,
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and may be freed soon after they are accessed.
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.TP
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.B POSIX_MADV_RANDOM
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The application expects to access the specified address range randomly.
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Thus, read ahead may be less useful than normally.
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.TP
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.B POSIX_MADV_WILLNEED
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The application expects to access the specified address range
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in the near future.
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Thus, read ahead may be beneficial.
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.TP
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.B POSIX_MADV_DONTNEED
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The application expects that it will not access the specified address range
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in the near future.
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.SH RETURN VALUE
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On success,
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.BR posix_madvise ()
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returns 0.
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On failure, it returns a positive error number.
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.SH ERRORS
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.TP
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.B EINVAL
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.I addr
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is not a multiple of the system page size or
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.I len
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is negative.
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.TP
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.B EINVAL
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.I advice
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is invalid.
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.TP
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.B ENOMEM
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Addresses in the specified range are partially or completely outside
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the caller's address space.
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.SH VERSIONS
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Support for
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.BR posix_madvise ()
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first appeared in glibc version 2.2.
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH NOTES
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POSIX.1 permits an implementation to generate an error if
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.I len
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is 0.
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On Linux, specifying
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.I len
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as 0 is permitted (as a successful no-op).
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In glibc, this function is implemented using
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.BR madvise (2).
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However, since glibc 2.6,
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.BR POSIX_MADV_DONTNEED
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is treated as a no-op, because the corresponding
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.BR madvise (2)
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value,
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.BR MADV_DONTNEED ,
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has destructive semantics.
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.SH SEE ALSO
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.BR madvise (2),
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.BR posix_fadvise (2)
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