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)).
The advice argument is one of the following values:
See madvise(2).
See madvise(2).
See madvise(2).
See madvise(2).
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.)
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 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.
pidfd is not a valid PID file descriptor.
The memory described by iovec is outside the accessible
address space of the process referred to by pidfd.
flags is not 0.
The sum of the iov_len values of iovec overflows a
ssize_t value.
n is too large.
Could not allocate memory for internal copies of the iovec
structures.
The caller does not have permission to access the address space of
the process pidfd.
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)