.\" Copyright (C) 2021 Suren Baghdasaryan .\" and Copyright (C) 2021 Minchan Kim .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" Commit ecb8ac8b1f146915aa6b96449b66dd48984caacc .\" .TH PROCESS_MADVISE 2 2021-06-20 "Linux" "Linux Programmer's Manual" .SH NAME process_madvise \- give advice about use of memory to a process .SH SYNOPSIS .nf .BR "#include " " /* Definition of " MADV_* " constants */" .BR "#include " " /* Definition of " SYS_* " constants */" .BR "#include " " /* Definition of " "struct iovec" " type */" .B #include .PP .BI "ssize_t syscall(SYS_process_madvise, int " pidfd , .BI " const struct iovec *" iovec ", size_t " vlen \ ", int " advice , .BI " unsigned int " flags ");" .fi .PP .IR Note : glibc provides no wrapper for .BR process_madvise (), necessitating the use of .BR syscall (2). .\" FIXME: See .SH DESCRIPTION The .BR 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 .I iovec and .IR vlen . The goal of such advice is to improve system or application performance. .PP The .I pidfd argument is a PID file descriptor (see .BR pidfd_open (2)) that specifies the process to which the advice is to be applied. .PP The pointer .I iovec points to an array of .I iovec structures, defined in .IR as: .PP .in +4n .EX struct iovec { void *iov_base; /* Starting address */ size_t iov_len; /* Length of region */ }; .EE .in .PP The .I iovec structure describes address ranges beginning at .I iov_base address and with the size of .I iov_len bytes. .PP The .I vlen specifies the number of elements in the .I iovec structure. This value must be less than or equal to .BR IOV_MAX (defined in .I or accessible via the call .IR sysconf(_SC_IOV_MAX) ). .PP The .I advice argument is one of the following values: .TP .BR MADV_COLD See .BR madvise (2). .TP .BR MADV_PAGEOUT See .BR madvise (2). .PP The .I flags argument is reserved for future use; currently, this argument must be specified as 0. .PP The .I vlen and .I iovec arguments are checked before applying any advice. If .I vlen is too big, or .I iovec is invalid, then an error will be returned immediately and no advice will be applied. .PP The advice might be applied to only a part of .I 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.) .PP Permission to apply advice to another process is governed by a ptrace access mode .B PTRACE_MODE_READ_REALCREDS check (see .BR ptrace (2)); in addition, because of the performance implications of applying the advice, the caller must have the .B CAP_SYS_ADMIN capability. .SH RETURN VALUE On success, .BR 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 .I iovec elements were already processed. The caller should check the return value to determine whether a partial advice occurred. .PP On error, \-1 is returned and .I errno is set to indicate the error. .SH ERRORS .TP .B EBADF .I pidfd is not a valid PID file descriptor. .TP .B EFAULT The memory described by .I iovec is outside the accessible address space of the process referred to by .IR pidfd . .TP .B EINVAL .I flags is not 0. .TP .B EINVAL The sum of the .I iov_len values of .I iovec overflows a .I ssize_t value. .TP .B EINVAL .I vlen is too large. .TP .B ENOMEM Could not allocate memory for internal copies of the .I iovec structures. .TP .B EPERM The caller does not have permission to access the address space of the process .IR pidfd . .TP .B ESRCH The target process does not exist (i.e., it has terminated and been waited on). .SH VERSIONS This system call first appeared in Linux 5.10. .\" commit ecb8ac8b1f146915aa6b96449b66dd48984caacc Support for this system call is optional, depending on the setting of the .B CONFIG_ADVISE_SYSCALLS configuration option. .SH CONFORMING TO The .BR process_madvise () system call is Linux-specific. .SH SEE ALSO .BR madvise (2), .BR pidfd_open (2), .BR process_vm_readv (2), .BR process_vm_write (2) .SH COLOPHON This page is part of release 5.13 of the Linux .I 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/.