process_madvise(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | SEE ALSO | COLOPHON

PROCESS_MADVISE(2)      Linux Programmer's Manual     PROCESS_MADVISE(2)

NAME         top

       process_madvise - give advice about use of memory to a process

SYNOPSIS         top

       #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         top

       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.

RETURN VALUE         top

       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         top

       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).

VERSIONS         top

       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.

CONFORMING TO         top

       The process_madvise() system call is Linux-specific.

SEE ALSO         top

       madvise(2), pidfd_open(2), process_vm_readv(2),
       process_vm_write(2)

COLOPHON         top

       This page is part of release 5.12 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-06-20             PROCESS_MADVISE(2)

Pages that refer to this page: madvise(2)pidfd_open(2)syscalls(2)