On Thu 28-01-21 23:03:40, 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> Reviewed-by: Michal Hocko <mhocko@xxxxxxxx> Thanks! > --- > 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 > > 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. > +It provides the advice to address ranges of process 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 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 > +.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. > +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. > +.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. > +.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. > +.SH ERRORS > +.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, > +.\" 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), > +.BR process_vm_readv (2), > +.BR process_vm_write (2) > -- > 2.30.0.365.g02bc693789-goog > -- Michal Hocko SUSE Labs
