дать совет по использованию памяти процессу (give advice about use of memory to a process)
Имя (Name)
process_madvise - give advice about use of memory to a process
Синопсис (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).
Описание (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 described by iovec and vlen. 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, defined
in <sys/uio.h> as:
struct iovec {
void *iov_base; /* Starting address */
size_t iov_len; /* Length of region */
};
The iovec structure describes address ranges beginning at
iov_base address and with the size of iov_len bytes.
The vlen specifies the number of elements in the iovec structure.
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_PAGEOUT
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
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.)
Permission to apply advice to another process is governed by a
ptrace access mode PTRACE_MODE_READ_REALCREDS check (see
ptrace(2)); in addition, because of the performance implications
of applying the advice, the caller must have the CAP_SYS_ADMIN
capability.
Возвращаемое значение (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.
Ошибки (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 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).
Версии (Versions)
This system call first appeared in Linux 5.10. Support for this
system call is optional, depending on the setting of the
CONFIG_ADVISE_SYSCALLS configuration option.
Стандарты (Conforming to)
The process_madvise() system call is Linux-specific.
Смотри также (See also)
madvise(2), pidfd_open(2), process_vm_readv(2),
process_vm_write(2)
