VMEVENT_FD(2) Linux Programmer's Manual VMEVENT_FD(2)
NAME vmevent_fd - Linux virtual memory management events
SYNOPSIS #define _GNU_SOURCE #include <unistd.h> #include <sys/syscall.h> #include <asm/unistd.h> #include <linux/types.h> #include <linux/vmevent.h>
syscall(__NR_vmevent_fd, config);
DESCRIPTION This system call creates a new file descriptor that can be used with polling routines (e.g. poll(2)) to get notified about vari- ous in-kernel virtual memory management events that might be of interest for userspace. The interface can also be used to effe- ciently monitor memory usage (e.g. number of idle and swap pages).
Applications can make overall system's memory management more nimble by adjusting theirs resources usage upon the notifica- tions.
Attributes Attributes are the basic concept, they are described by the fol- lowing structure:
struct vmevent_attr { __u64 value; __u32 type; __u32 state; };
type may correspond to these values:
VMEVENT_ATTR_NR_AVAIL_PAGES The attribute reports total number of available pages in the system, not including swap space (i.e. just total RAM). value is used to setup a threshold (in number or pages) upon which the event will be delivered by the ker- nel.
Upon notifications kernel updates all configured attributes, so the attribute is mostly used without any thresholds, just for getting the value together with other attributes and avoid reading and parsing /proc/vmstat.
VMEVENT_ATTR_NR_FREE_PAGES The attribute reports total number of unused (idle) RAM in the system.
value is used to setup a threshold (in number or pages) upon which the event will be delivered by the kernel.
VMEVENT_ATTR_NR_SWAP_PAGES The attribute reports total number of swapped pages.
value is used to setup a threshold (in number or pages) upon which the event will be delivered by the kernel.
VMEVENT_ATTR_PRESSURE The attribute reports Linux virtual memory management pressure. There are three discrete levels:
VMEVENT_PRESSURE_LOW: By setting the threshold to this value it's possible to watch whether system is reclaiming memory for new allocations. Monitoring reclaiming activity might be useful for maintaining overall system's cache level.
VMEVENT_PRESSURE_MED: The system is experiencing medium memory pressure, there is some mild swapping activity. Upon this event applications may decide to free any resources that can be easily reconstructed or re-read from a disk.
VMEVENT_PRESSURE_OOM: The system is actively thrashing, it is about to out of memory (OOM) or even the in-kernel OOM killer is on its way to trigger. Applications should do whatever they can to help the system. See proc(5) for more information about OOM killer and its configuration options.
value is used to setup a threshold upon which the event will be delivered by the kernel (for algebraic compar- isons, it is defined that VMEVENT_PRESSURE_LOW < VMEVENT_PRESSURE_MED < VMEVENT_PRESSURE_OOM, but applica- tions should not put any meaning into the absolute val- ues.)
state is used to setup thresholds' behaviour, the following flags can be bitwise OR'ed:
VMEVENT_ATTR_STATE_VALUE_LT Notification will be delivered when an attribute is less than a user-specified value.
VMEVENT_ATTR_STATE_VALUE_GT Notifications will be delivered when an attribute is greater than a user-specified value.
VMEVENT_ATTR_STATE_VALUE_EQ Notifications will be delivered when an attribute is equal to a user-specified value.
VMEVENT_ATTR_STATE_EDGE_TRIGGER Events will be only delivered when an attribute crosses value threshold.
Events Upon a notification, application must read out events using read(2) system call. The events are delivered using the follow- ing structure:
struct vmevent_event { __u32 counter; __u32 padding; struct vmevent_attr attrs[]; };
The counter specifies a number of reported attributes, and the attrs array contains a copy of configured attributes, with vmevent_attr's value overwritten to attribute's value.
Config vmevent_fd(2) accepts vmevent_config structure to configure the notifications:
struct vmevent_config { __u32 size; __u32 counter; __u64 sample_period_ns; struct vmevent_attr attrs[VMEVENT_CONFIG_MAX_ATTRS]; };
size must be initialized to sizeof(struct vmevent_config).
counter specifies a number of initialized attrs elements.
sample_period_ns specifies sampling period in nanoseconds. For applications it is recommended to set this value to a highest suitable period. (Note that for some attributes the delivery tim- ing is not based on the sampling period, e.g. VMEVENT_ATTR_PRES- SURE.)
RETURN VALUE On success, vmevent_fd() returns a new file descriptor. On error, a negative value is returned and errno is set to indicate the error.
ERRORS vmevent_fd() can fail with errors similar to open(2).
In addition, the following errors are possible:
EINVAL The failure means that an improperly initalized config structure has been passed to the call (this also includes improperly initialized attrs arrays).
EFAULT The failure means that the kernel was unable to read the configuration structure, that is, config parameter points to an inaccessible memory.
VERSIONS The system call is available on Linux since kernel 3.8. Library support is yet not provided by any glibc version.
CONFORMING TO The system call is Linux-specific.
EXAMPLE Examples can be found in /usr/src/linux/tools/testing/vmevent/ directory.
SEE ALSO poll(2), read(2), proc(5), vmstat(8)
Linux 2012-10-16 VMEVENT_FD(2)
Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- man2/vmevent_fd.2 | 235 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 235 insertions(+) create mode 100644 man2/vmevent_fd.2
diff --git a/man2/vmevent_fd.2 b/man2/vmevent_fd.2 new file mode 100644 index 0000000..b631455 --- /dev/null +++ b/man2/vmevent_fd.2 @@ -0,0 +1,235 @@ +." Copyright (C) 2008 Michael Kerrisk mtk.manpages@gmail.com +." Copyright (C) 2012 Linaro Ltd. +." Anton Vorontsov anton.vorontsov@linaro.org +." Based on ideas from: +." KOSAKI Motohiro, Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka +." Enberg. +." +." This program is free software; you can redistribute it and/or modify +." it under the terms of the GNU General Public License as published by +." the Free Software Foundation; either version 2 of the License, or +." (at your option) any later version. +." +." This program is distributed in the hope that it will be useful, +." but WITHOUT ANY WARRANTY; without even the implied warranty of +." MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +." GNU General Public License for more details. +." +." You should have received a copy of the GNU General Public License +." along with this program; if not, write to the Free Software +." Foundation, Inc., 59 Temple Place, Suite 330, Boston, +." MA 02111-1307 USA +." +.TH VMEVENT_FD 2 2012-10-16 Linux "Linux Programmer's Manual" +.SH NAME +vmevent_fd - Linux virtual memory management events +.SH SYNOPSIS +.nf +.B #define _GNU_SOURCE +.B #include <unistd.h> +.B #include <sys/syscall.h> +.B #include <asm/unistd.h> +.B #include <linux/types.h> +.B #include <linux/vmevent.h> + +." TODO: libc wrapper +.BI "syscall(__NR_vmevent_fd, "config ); +.fi +.SH DESCRIPTION +This system call creates a new file descriptor that can be used with polling +routines (e.g. +.BR poll (2)) +to get notified about various in-kernel virtual memory management events +that might be of interest for userspace. The interface can +also be used to effeciently monitor memory usage (e.g. number of idle and +swap pages). + +Applications can make overall system's memory management more nimble by +adjusting theirs resources usage upon the notifications. +.SS Attributes +Attributes are the basic concept, they are described by the following +structure: + +.nf +struct vmevent_attr { + __u64 value; + __u32 type; + __u32 state; +}; +.fi + +.I type +may correspond to these values: +.TP +.B VMEVENT_ATTR_NR_AVAIL_PAGES +The attribute reports total number of available pages in the system, not +including swap space (i.e. just total RAM). +.I value +is used to setup a threshold (in number or pages) upon which the event +will be delivered by the kernel. + +Upon notifications kernel updates all configured attributes, so the +attribute is mostly used without any thresholds, just for getting the +value together with other attributes and avoid reading and parsing +.IR /proc/vmstat . +.TP +.B VMEVENT_ATTR_NR_FREE_PAGES +The attribute reports total number of unused (idle) RAM in the system. + +.I value +is used to setup a threshold (in number or pages) upon which the event +will be delivered by the kernel. +.TP +.B VMEVENT_ATTR_NR_SWAP_PAGES +The attribute reports total number of swapped pages. + +.I value +is used to setup a threshold (in number or pages) upon which the event +will be delivered by the kernel. +.TP +.B VMEVENT_ATTR_PRESSURE +The attribute reports Linux virtual memory management pressure. There are +three discrete levels: + +.BR VMEVENT_PRESSURE_LOW : +By setting the threshold to this value it's possible to watch whether +system is reclaiming memory for new allocations. Monitoring reclaiming +activity might be useful for maintaining overall system's cache level. + +.BR VMEVENT_PRESSURE_MED : +The system is experiencing medium memory pressure, there is some mild +swapping activity. Upon this event applications may decide to free any +resources that can be easily reconstructed or re-read from a disk. + +.BR VMEVENT_PRESSURE_OOM : +The system is actively thrashing, it is about to out of memory (OOM) or +even the in-kernel OOM killer is on its way to trigger. Applications +should do whatever they can to help the system. See +.BR proc (5) +for more information about OOM killer and its configuration options. + +.I value +is used to setup a threshold upon which the event will be delivered by +the kernel (for algebraic comparisons, it is defined that +.BR VMEVENT_PRESSURE_LOW " <" +.BR VMEVENT_PRESSURE_MED " <" +.BR VMEVENT_PRESSURE_OOM , +but applications should not put any meaning into the absolute values.) + +.TP +.I state +is used to setup thresholds' behaviour, the following flags can be bitwise +OR'ed: +.... +.TP +.B VMEVENT_ATTR_STATE_VALUE_LT +Notification will be delivered when an attribute is less than a +user-specified +.IR "value" . +.TP +.B VMEVENT_ATTR_STATE_VALUE_GT +Notifications will be delivered when an attribute is greater than a +user-specified +.IR "value" . +.TP +.B VMEVENT_ATTR_STATE_VALUE_EQ +Notifications will be delivered when an attribute is equal to a +user-specified +.IR "value" . +.TP +.B VMEVENT_ATTR_STATE_EDGE_TRIGGER +Events will be only delivered when an attribute crosses +.I value +threshold. +.SS Events +Upon a notification, application must read out events using +.BR read (2) +system call. +The events are delivered using the following structure: + +.nf +struct vmevent_event { + __u32 counter; + __u32 padding; + struct vmevent_attr attrs[]; +}; +.fi + +The +.I counter +specifies a number of reported attributes, and the +.I attrs +array contains a copy of configured attributes, with +.IR "vmevent_attr" 's +.I value +overwritten to attribute's value. +.SS Config +.BR vmevent_fd (2) +accepts +.I vmevent_config +structure to configure the notifications: + +.nf +struct vmevent_config { + __u32 size; + __u32 counter; + __u64 sample_period_ns; + struct vmevent_attr attrs[VMEVENT_CONFIG_MAX_ATTRS]; +}; +.fi + +.I size +must be initialized to +.IR "sizeof(struct vmevent_config)" . + +.I counter +specifies a number of initialized +.I attrs +elements. + +.I sample_period_ns +specifies sampling period in nanoseconds. For applications it is +recommended to set this value to a highest suitable period. (Note that for +some attributes the delivery timing is not based on the sampling period, +e.g. +.IR VMEVENT_ATTR_PRESSURE .) +.SH "RETURN VALUE" +On success, +.BR vmevent_fd () +returns a new file descriptor. On error, a negative value is returned and +.I errno +is set to indicate the error. +.SH ERRORS +.BR vmevent_fd () +can fail with errors similar to +.BR open (2). + +In addition, the following errors are possible: +.TP +.B EINVAL +The failure means that an improperly initalized +.I config +structure has been passed to the call (this also includes improperly +initialized +.I attrs +arrays). +.TP +.B EFAULT +The failure means that the kernel was unable to read the configuration +structure, that is, +.I config +parameter points to an inaccessible memory. +.SH VERSIONS +The system call is available on Linux since kernel 3.8. Library support is +yet not provided by any glibc version. +.SH CONFORMING TO +The system call is Linux-specific. +.SH EXAMPLE +Examples can be found in +.I /usr/src/linux/tools/testing/vmevent/ +directory. +.SH "SEE ALSO" +.BR poll (2), +.BR read (2), +.BR proc (5), +.BR vmstat (8)