process_madvise(2) — Linux manual page

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>

       ssize_t process_madvise(int pidfd, const struct iovec iovec[.n],
                               size_t n, int advice, unsigned int flags);

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 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:

       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 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)).

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 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.

STANDARDS

       Linux.

HISTORY

       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.

SEE ALSO

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

COLOPHON

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Linux man-pages 6.9.1          2024-05-02             process_madvise(2)

Pages that refer to this page: madvise(2), pidfd_open(2), syscalls(2), iovec(3type)

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