mirror of https://github.com/mkerrisk/man-pages
216 lines
5.2 KiB
Groff
216 lines
5.2 KiB
Groff
.\" Copyright (C) 2021 Suren Baghdasaryan <surenb@google.com>
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.\" and Copyright (C) 2021 Minchan Kim <minchan@kernel.org>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" Commit ecb8ac8b1f146915aa6b96449b66dd48984caacc
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.\"
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.TH PROCESS_MADVISE 2 2021-01-12 "Linux" "Linux Programmer's Manual"
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.SH NAME
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process_madvise \- give advice about use of memory to a process
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.SH SYNOPSIS
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.nf
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.B #include <sys/uio.h>
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.PP
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.BI "ssize_t process_madvise(int " pidfd ", const struct iovec *" iovec ,
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.BI " size_t " vlen ", int " advice ,
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.BI " unsigned int " flags ");"
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.fi
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.PP
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.IR Note :
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There is no glibc wrapper for this system call; see NOTES.
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.\" FIXME: See <https://sourceware.org/bugzilla/show_bug.cgi?id=27380>
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.SH DESCRIPTION
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The
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.BR process_madvise()
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system call is used to give advice or directions to the kernel about the
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address ranges of another process or of the calling process.
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It provides the advice for the address ranges described by
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.I iovec
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and
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.IR vlen .
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The goal of such advice is to improve system or application performance.
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.PP
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The
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.I pidfd
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argument is a PID file descriptor (see
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.BR pidfd_open (2))
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that specifies the process to which the advice is to be applied.
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.PP
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The pointer
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.I iovec
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points to an array of
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.I iovec
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structures, defined in
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.IR <sys/uio.h>
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as:
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.PP
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.in +4n
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.EX
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struct iovec {
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void *iov_base; /* Starting address */
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size_t iov_len; /* Length of region */
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};
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.EE
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.in
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.PP
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The
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.I iovec
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structure describes address ranges beginning at
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.I iov_base
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address and with the size of
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.I iov_len
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bytes.
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.PP
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The
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.I vlen
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specifies the number of elements in the
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.I iovec
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structure.
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This value must be less than or equal to
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.BR IOV_MAX
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(defined in
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.I <limits.h>
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or accessible via the call
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.IR sysconf(_SC_IOV_MAX) ).
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.PP
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The
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.I advice
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argument is one of the following values:
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.TP
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.BR MADV_COLD
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See
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.BR madvise (2).
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.TP
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.BR MADV_PAGEOUT
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See
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.BR madvise (2).
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.PP
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The
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.I flags
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argument is reserved for future use; currently, this argument must be
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specified as 0.
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.PP
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The
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.I vlen
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and
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.I iovec
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arguments are checked before applying any advice.
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If
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.I vlen
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is too big, or
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.I iovec
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is invalid,
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then an error will be returned immediately and no advice will be applied.
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.PP
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The advice might be applied to only a part of
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.I iovec
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if one of its elements points to an invalid memory region in the
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remote process.
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No further elements will be processed beyond that point.
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(See the discussion regarding partial advice in RETURN VALUE.)
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.PP
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Permission to apply advice to another process is governed by a
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ptrace access mode
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.B PTRACE_MODE_READ_REALCREDS
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check (see
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.BR ptrace (2));
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in addition,
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because of the performance implications of applying the advice,
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the caller must have the
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.B CAP_SYS_ADMIN
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capability.
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.SH RETURN VALUE
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On success,
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.BR process_madvise ()
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returns the number of bytes advised.
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This return value may be less than the total number of requested bytes,
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if an error occurred after some
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.I iovec
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elements were already processed.
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The caller should check the return value to determine whether a partial
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advice occurred.
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.PP
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On error, \-1 is returned and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EBADF
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.I pidfd
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is not a valid PID file descriptor.
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.TP
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.B EFAULT
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The memory described by
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.I iovec
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is outside the accessible address space of the process referred to by
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.IR pidfd .
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.TP
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.B EINVAL
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.I flags
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is not 0.
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.TP
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.B EINVAL
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The sum of the
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.I iov_len
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values of
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.I iovec
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overflows a
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.I ssize_t
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value.
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.TP
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.B EINVAL
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.I vlen
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is too large.
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.TP
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.B ENOMEM
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Could not allocate memory for internal copies of the
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.I iovec
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structures.
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.TP
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.B EPERM
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The caller does not have permission to access the address space of the process
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.IR pidfd .
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.TP
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.B ESRCH
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The target process does not exist (i.e., it has terminated and been waited on).
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.SH VERSIONS
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This system call first appeared in Linux 5.10.
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.\" commit ecb8ac8b1f146915aa6b96449b66dd48984caacc
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Support for this system call is optional,
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depending on the setting of the
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.B CONFIG_ADVISE_SYSCALLS
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configuration option.
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.SH CONFORMING TO
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The
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.BR process_madvise ()
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system call is Linux-specific.
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.SH NOTES
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Glibc does not provide a wrapper for this system call; call it using
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.BR syscall (2).
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.SH SEE ALSO
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.BR madvise (2),
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.BR pidfd_open (2),
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.BR process_vm_readv (2),
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.BR process_vm_write (2)
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