Hello Suren, Thank you for writing this page! Some comments below. On Wed, 20 Jan 2021 at 21:36, Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > Initial version of process_madvise(2) manual page. Initial text was > extracted from [1], amended after fix [2] and more details added using > man pages of madvise(2) and process_vm_read(2) as examples. It also > includes the changes to required permission proposed in [3]. > > [1] https://lore.kernel.org/patchwork/patch/1297933/ > [2] https://lkml.org/lkml/2020/12/8/1282 > [3] https://patchwork.kernel.org/project/selinux/patch/20210111170622.2613577-1-surenb@xxxxxxxxxx/#23888311 > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > --- > > Adding the plane text version for ease of review: Thanks for adding the rendered version. I will make my comments against the source, below. > NAME > process_madvise - give advice about use of memory to a process > > SYNOPSIS > #include <sys/uio.h> > > ssize_t process_madvise(int pidfd, > const struct iovec *iovec, > unsigned long vlen, > 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 from external process as well as local > process. It provides the advice to address ranges of process described by > iovec and vlen. The goal of such advice is to improve system or application > performance. > > The pidfd selects the process referred to by the PID file descriptor > specified in pidfd. (see pidofd_open(2) for further information). > > 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; /* Number of bytes to transfer */ > }; > > The iovec describes address ranges beginning at iov_base address and with > the size of iov_len bytes. > > The vlen represents the number of elements in iovec. > > The advice can be one of the values listed below. > > Linux-specific advice values > The following Linux-specific advice values have no counterparts in the > POSIX-specified posix_madvise(3), and may or may not have counterparts in > the madvise() interface available on other implementations. > > MADV_COLD (since Linux 5.4.1) > Deactivate a given range of pages by moving them from active to > inactive LRU list. This is done to accelerate the reclaim of these > pages. The advice might be ignored for some pages in the range when it > is not applicable. > MADV_PAGEOUT (since Linux 5.4.1) > Reclaim a given range of pages. This is done to free up memory occupied > by these pages. If a page is anonymous it will be swapped out. If a > page is file-backed and dirty it will be written back into the backing > storage. The advice might be ignored for some pages in the range when > it is not applicable. > > The flags argument is reserved for future use; currently, this argument must > be specified as 0. > > The value specified in the vlen argument must be less than or equal to > IOV_MAX (defined in <limits.h> or accessible via the call > sysconf(_SC_IOV_MAX)). > > The vlen and iovec arguments are checked before applying any hints. If the > vlen is too big, or iovec is invalid, an error will be returned > immediately. > > Hint might be applied to 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. > > Permission to provide a hint to external process is governed by a ptrace > access mode PTRACE_MODE_READ_REALCREDS check; see ptrace(2) and > CAP_SYS_ADMIN capability that caller should have in order to affect > performance of an external process. > > 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. The caller should check return value to determine whether > a partial advice occurred. So there are three return values possible, > ERRORS > EFAULT The memory described by iovec is outside the accessible address > space of the process pid. s/pid/ of the process referred to by .IR 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 No process with ID pidfd exists. > > VERSIONS > Since Linux 5.10, support for this system call is optional, depending on > the setting of the CONFIG_ADVISE_SYSCALLS configuration option. > > SEE ALSO > madvise(2), pidofd_open(2), process_vm_readv(2), process_vm_write(2) > > man2/process_madvise.2 | 208 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 208 insertions(+) > create mode 100644 man2/process_madvise.2 > > diff --git a/man2/process_madvise.2 b/man2/process_madvise.2 > new file mode 100644 > index 000000000..9bb5cb5ed > --- /dev/null > +++ b/man2/process_madvise.2 > @@ -0,0 +1,208 @@ > +.\" Copyright (C) 2021 Suren Baghdasaryan <surenb@xxxxxxxxxx> > +.\" and Copyright (C) 2021 Minchan Kim <minchan@xxxxxxxxxx> > +.\" > +.\" %%%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 2021-01-12 "Linux" "Linux Programmer's Manual" > +.SH NAME > +process_madvise \- give advice about use of memory to a process > +.SH SYNOPSIS > +.nf > +.B #include <sys/uio.h> > +.PP > +.BI "ssize_t process_madvise(int " pidfd , > +.BI " const struct iovec *" iovec , > +.BI " unsigned long " vlen , > +.BI " int " advice , > +.BI " unsigned int " flags ");" > +.fi > +.SH DESCRIPTION > +The > +.BR process_madvise() > +system call is used to give advice or directions > +to the kernel about the address ranges from external process as well as s/from external/of other/ > +local process. It provides the advice to address ranges of process s/local/of the calling/ Please start new sentence on new lines. (See the discussion of semantic newlines in man-pages(7).) > +described by > +.I iovec > +and > +.I vlen\. > +The goal of such advice is to improve system or application performance. > +.PP > +The > +.I pidfd > +selects the process referred to by the PID file descriptor > +specified in pidfd. (see > +.BR pidofd_open(2) > +for further information). Rewrite the previous as: [[ The .I pidfd argument is a PID file descriptor (see .BR pidofd_open (2)) that specifies the process to which the advice is to be applied. > +.PP > +The pointer > +.I iovec > +points to an array of iovec structures, defined in "iovec" should be formatted as .I iovec > +.IR <sys/uio.h> > +as: > +.PP > +.in +4n > +.EX > +struct iovec { > + void *iov_base; /* Starting address */ > + size_t iov_len; /* Number of bytes to transfer */ > +}; > +.EE > +.in > +.PP > +The > +.I iovec > +describes address ranges beginning at s/describes/structure describes/ > +.I iov_base > +address and with the size of > +.I iov_len > +bytes. > +.PP > +The > +.I vlen > +represents the number of elements in > +.I iovec\. ==> the .IR iovec structure. > +.PP > +The > +.I advice > +can be one of the values listed below. s/can be/argument is/ > +.\" > +.\" ====================================================================== > +.\" > +.SS Linux-specific advice values > +The following Linux-specific > +.I advice > +values have no counterparts in the POSIX-specified > +.BR posix_madvise (3), > +and may or may not have counterparts in the > +.BR madvise () > +interface available on other implementations. > +.TP > +.BR MADV_COLD " (since Linux 5.4.1)" > +.\" commit 9c276cc65a58faf98be8e56962745ec99ab87636 > +Deactivate a given range of pages by moving them from active to inactive > +LRU list. This is done to accelerate the reclaim of these pages. The advice New sentences on new lines. > +might be ignored for some pages in the range when it is not applicable. > +.TP > +.BR MADV_PAGEOUT " (since Linux 5.4.1)" > +.\" commit 1a4e58cce84ee88129d5d49c064bd2852b481357 > +Reclaim a given range of pages. This is done to free up memory occupied by > +these pages. If a page is anonymous it will be swapped out. If a page is > +file-backed and dirty it will be written back into the backing storage. s/into/to/ > +The advice might be ignored for some pages in the range when it is not > +applicable. > +.PP > +The > +.I flags > +argument is reserved for future use; currently, this argument must be > +specified as 0. > +.PP > +The value specified in the > +.I vlen > +argument must be less than or equal to > +.BR IOV_MAX > +(defined in > +.I <limits.h> > +or accessible via the call > +.IR sysconf(_SC_IOV_MAX) ). > +.PP > +The > +.I vlen > +and > +.I iovec > +arguments are checked before applying any hints. > +If the > +.I vlen > +is too big, or > +.I iovec > +is invalid, an error will be returned immediately. > +.PP > +Hint might be applied to a part of s/Hint/The hint/ > +.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. > +.PP > +Permission to provide a hint to external process is governed by a > +ptrace access mode > +.B PTRACE_MODE_READ_REALCREDS > +check; see > +.BR ptrace (2) > +and > +.B CAP_SYS_ADMIN > +capability that caller should have in order to affect performance > +of an external process. The preceding sentence is garbled. Missing words? > +.SH 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. The caller should check return value > +to determine whether a partial advice occurred. > +.SH ERRORS > +.TP > +.B EFAULT > +The memory described by > +.I iovec > +is outside the accessible address space of the process pid. s/process pid./ 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 ssize_t value. .I ssize_t > +.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 > +.I pidfd. .IR pidfd . > +.TP > +.B ESRCH > +No process with ID > +.I pidfd > +exists. Should this maybe be: [[ The target process does not exist (i.e., it has terminated and been waited on). ]] See pidfd_send_signal(2). Also, is an EBADF error possible? Again, see pidfd_send_signal(2). > +.SH VERSIONS > +Since Linux 5.10, Better: This system call first appeared in Linux 5.10. > +.\" commit ecb8ac8b1f146915aa6b96449b66dd48984caacc > +support for this system call is optional, s/support/Support/ > +depending on the setting of the > +.B CONFIG_ADVISE_SYSCALLS > +configuration option. > +.SH SEE ALSO > +.BR madvise (2), > +.BR pidofd_open(2), > +.BR process_vm_readv (2), > +.BR process_vm_write (2) Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
