process_madvise(2) System Calls Manual process_madvise(2)
NAME
process_madvise - give advice about use of memory to a process
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <sys/mman.h> /* Definition of MADV_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <sys/uio.h> /* Definition of struct iovec type */
#include <unistd.h>
ssize_t syscall(SYS_process_madvise, int pidfd,
const struct iovec *iovec, size_t vlen, int advice,
unsigned int flags);
Note: glibc provides no wrapper for process_madvise(), necessitating
the use of syscall(2).
DESCRIPTION
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 de-
scribed by iovec and vlen. The goal of such advice is to improve sys-
tem 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).
vlen 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)).
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).
The flags argument is reserved for future use; currently, this argument
must be specified as 0.
The vlen and iovec arguments are checked before applying any advice.
If vlen 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 ele-
ments points to an invalid memory region in the remote process. No
further elements will be processed beyond that point. (See the discus-
sion regarding partial advice in RETURN VALUE.)
Starting in 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 ap-
plying the advice, the caller must have the CAP_SYS_NICE capability
(see capabilities(7)).
RETURN VALUE
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.
ERRORS
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 vlen 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.
VERSIONS
This system call first appeared in Linux 5.10. Support for this system
call is optional, depending on the setting of the CONFIG_AD-
VISE_SYSCALLS configuration option.
STANDARDS
The process_madvise() system call is Linux-specific.
NOTES
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.
SEE ALSO
madvise(2), pidfd_open(2), process_vm_readv(2), process_vm_write(2)
Linux man-pages 6.03 2022-11-01 process_madvise(2)
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