On Sat, Jan 30, 2021 at 1:34 PM Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > > Hello Suren, > > Thank you for the revisions! Just a few more comments: all pretty small > stuff (many points that I overlooked the first time rround), since the > page already looks pretty good by now. > > Again, thanks for the rendered version. As before, I've added my > comments to the page source. Hi Michael, Thanks for reviewing! > > On 1/29/21 8:03 AM, Suren Baghdasaryan 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> > > --- > > changes in v2: > > - Changed description of MADV_COLD per Michal Hocko's suggestion > > - Appled fixes suggested by Michael Kerrisk > > > > NAME > > process_madvise - give advice about use of memory to a process > > s/-/\-/ ack > > > > > 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 of other process as well as of > > the calling 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 argument is a PID file descriptor (see pidofd_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; /* Number of bytes to transfer */ > > }; > > > > The iovec structure describes address ranges beginning at iov_base address > > and with the size of iov_len bytes. > > > > The vlen represents the number of elements in the iovec structure. > > > > The advice argument is 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(2) interface available on other implementations. > > > > MADV_COLD (since Linux 5.4.1) > > Deactive a given range of pages which will make them a more probable > > reclaim target should there be a memory pressure. This is a non- > > destructive operation. 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 to 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. > > > > The 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 another process is governed by a ptrace > > access mode PTRACE_MODE_READ_REALCREDS check (see ptrace(2)); in addition, > > the caller must have the CAP_SYS_ADMIN capability due to performance > > implications of applying the hint. > > > > 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 > > 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). > > EBADF pidfd is not a valid PID file descriptor. > > > > 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. > > > > SEE ALSO > > madvise(2), pidofd_open(2), process_vm_readv(2), process_vm_write(2) > > > > man2/process_madvise.2 | 222 +++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 222 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..07553289f > > --- /dev/null > > +++ b/man2/process_madvise.2 > > @@ -0,0 +1,222 @@ > > +.\" 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 of other process as well as of the calling process. > > s/other/another/ > s/as well as of/or/ ack > > > +It provides the advice to address ranges of process described by > > s/address ranges of process/the address ranges/ ack > > > +.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 pidofd_open (2)) > > s/pidofd_open/pidfd_open/ > (I overlooked this last time.) ack > > > +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 <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 > > +structure describes address ranges beginning at > > +.I iov_base > > +address and with the size of > > +.I iov_len > > +bytes. > > +.PP > > +The > > +.I vlen > > +represents the number of elements in the > > +.I iovec > > +structure. > > +.PP > > +The > > +.I advice > > +argument is one of the values listed below. > > +.\" > > +.\" ====================================================================== > > +.\" > > +.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 (2) > > +interface available on other implementations. > > +.TP > > +.BR MADV_COLD " (since Linux 5.4.1)" > > +.\" commit 9c276cc65a58faf98be8e56962745ec99ab87636 > > +Deactive a given range of pages which will make them a more probable > > +reclaim target should there be a memory pressure. > > +This is a non-destructive operation. > > s/non-destructive/nondestructive/ ack > > > +The advice 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 to the backing > > +storage. > > +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. > > s/immediately/immediately and no advice will be applied/ ? > > That's just a guess on my part. Is it correct? Correct. Will change. > > > +.PP > > +The hint might be applied to 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. > > +.PP > > +Permission to provide a hint to another process is governed by a > > +ptrace access mode > > +.B PTRACE_MODE_READ_REALCREDS > > +check (see > > +.BR ptrace (2)); > > +in addition, the caller must have the > > +.B CAP_SYS_ADMIN > > +capability due to performance implications of applying the hint. > > Great addition. Thanks. ack > > > +.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 after some 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. > > Thanks. That's better! ack > > > +.SH ERRORS > > I should have mentioned this last time: could you place the errors > in alphabetical order please. ack > > > +.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). > > +.TP > > +.B EBADF > > +.I pidfd > > +is not a valid PID file descriptor. > > +.SH VERSIONS > > +This system call first appeared in Linux 5.10, > > s/,/./ ack > > > +.\" commit ecb8ac8b1f146915aa6b96449b66dd48984caacc > > +Support for this system call is optional, > > +depending on the setting of the > > +.B CONFIG_ADVISE_SYSCALLS > > +configuration option. > > +.SH SEE ALSO > > +.BR madvise (2), > > +.BR pidofd_open(2), > > s/pidofd_open/pidfd_open/ ack > > > +.BR process_vm_readv (2), > > +.BR process_vm_write (2) > > Cheers, > > Michael > I will post v3 with Michal's Reviewed-by and your comments addressed later today. Thanks again for your time! Suren. > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/
