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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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process_madvise(2) System Calls Manual process_madvise(2)
process_madvise - give advice about use of memory to a process
Standard C library (libc, -lc)
#include <sys/mman.h>
ssize_t process_madvise(int pidfd, const struct iovec iovec[.n],
size_t n, int advice, unsigned int flags);
The process_madvise() system call is used to give advice or
directions to the kernel about the address ranges of another
process or of the calling process. It provides the advice for the
address ranges described by iovec and n. The goal of such advice
is to improve system or application performance.
The pidfd argument is a PID file descriptor (see pidfd_open(2))
that specifies the process to which the advice is to be applied.
The pointer iovec points to an array of iovec structures,
described in iovec(3type).
n specifies the number of elements in the array of iovec
structures. This value must be less than or equal to IOV_MAX
(defined in <limits.h> or accessible via the call
sysconf(_SC_IOV_MAX)).
If manipulating another process, or before Linux 6.13, the advice
argument is one of the following values:
MADV_COLD
See madvise(2).
MADV_COLLAPSE
See madvise(2).
MADV_PAGEOUT
See madvise(2).
MADV_WILLNEED
See madvise(2).
Since Linux 6.13, when manipulating the calling process, any
advice flag is permitted.
The flags argument is reserved for future use; currently, this
argument must be specified as 0.
The n and iovec arguments are checked before applying any advice.
If n is too big, or iovec is invalid, then an error will be
returned immediately and no advice will be applied.
The advice might be applied to only a part of iovec if one of its
elements points to an invalid memory region in the remote process.
No further elements will be processed beyond that point. (See the
discussion regarding partial advice in RETURN VALUE.)
Since Linux 5.12, permission to apply advice to another process is
governed by ptrace access mode PTRACE_MODE_READ_FSCREDS check (see
ptrace(2)); in addition, because of the performance implications
of applying the advice, the caller must have the CAP_SYS_NICE
capability (see capabilities(7)).
On success, process_madvise() returns the number of bytes advised.
This return value may be less than the total number of requested
bytes, if an error occurred after some iovec elements were already
processed. The caller should check the return value to determine
whether a partial advice occurred.
On error, -1 is returned and errno is set to indicate the error.
EBADF pidfd is not a valid PID file descriptor.
EFAULT The memory described by iovec is outside the accessible
address space of the process referred to by pidfd.
EINVAL flags is not 0.
EINVAL The sum of the iov_len values of iovec overflows a ssize_t
value.
EINVAL n is too large.
ENOMEM Could not allocate memory for internal copies of the iovec
structures.
EPERM The caller does not have permission to access the address
space of the process pidfd.
ESRCH The target process does not exist (i.e., it has terminated
and been waited on).
See madvise(2) for advice-specific errors.
Linux.
Linux 5.10. glibc 2.36.
Support for this system call is optional, depending on the setting
of the CONFIG_ADVISE_SYSCALLS configuration option.
When this system call first appeared in Linux 5.10, permission to
apply advice to another process was entirely governed by ptrace
access mode PTRACE_MODE_ATTACH_FSCREDS check (see ptrace(2)).
This requirement was relaxed in Linux 5.12 so that the caller
didn't require full control over the target process.
madvise(2), pidfd_open(2), process_vm_readv(2),
process_vm_write(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.10.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.10 2024-12-04 process_madvise(2)
Pages that refer to this page: madvise(2), pidfd_open(2), syscalls(2), iovec(3type)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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