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mempress: change default PSI window duration to 2s

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This changes the PSI window duration we default to for watching memory
pressure events from 1s to 2s. This is because apparently the kernel
will soon disallow window durations other than 2s for unprivileged
processes.

Hence, we'll bump the threshold from 100m to 200ms, and the window from
1s to 2s.
This commit is contained in:
Lennart Poettering 2023-03-09 12:34:23 +01:00
parent 2208d96623
commit a617007417
5 changed files with 9 additions and 7 deletions
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2
man/systemd-system.conf.xml
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@ -565,7 +565,7 @@
<varname>MemoryPressureWatch=</varname> and <varname>MemoryPressureThresholdSec=</varname>
settings. See
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details. Defaults to <literal>auto</literal> and <literal>100ms</literal>, respectively. This
for details. Defaults to <literal>auto</literal> and <literal>200ms</literal>, respectively. This
also sets the memory pressure monitoring threshold for the service manager itself.</para></listitem>
</varlistentry>
</variablelist>

4
man/systemd.resource-control.xml
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@ -1332,10 +1332,10 @@ DeviceAllow=/dev/loop-control
<listitem><para>Sets the memory pressure threshold time for memory pressure monitor as configured via
<varname>MemoryPressureWatch=</varname>. Specifies the maximum allocation latency before a memory
pressure event is signalled to the service, per 1s window. If not specified defaults to the
pressure event is signalled to the service, per 2s window. If not specified defaults to the
<varname>DefaultMemoryPressureThresholdSec=</varname> setting in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
(which in turn defaults to 100ms). The specified value expects a time unit such as
(which in turn defaults to 200ms). The specified value expects a time unit such as
<literal>ms</literal> or <literal>µs</literal>, see
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details on the permitted syntax.</para></listitem>

4
src/basic/psi-util.h
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@ -31,5 +31,5 @@ int is_pressure_supported(void);
/* Default parameters for memory pressure watch logic in sd-event and PID 1 */
#define MEMORY_PRESSURE_DEFAULT_TYPE "some"
#define MEMORY_PRESSURE_DEFAULT_THRESHOLD_USEC (100 * USEC_PER_MSEC)
#define MEMORY_PRESSURE_DEFAULT_WINDOW_USEC USEC_PER_SEC
#define MEMORY_PRESSURE_DEFAULT_THRESHOLD_USEC (200 * USEC_PER_MSEC)
#define MEMORY_PRESSURE_DEFAULT_WINDOW_USEC (2 * USEC_PER_SEC)

4
src/libsystemd/sd-event/sd-event.c
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@ -2005,7 +2005,9 @@ _public_ int sd_event_add_memory_pressure(
* some 100000 1000000
* full 100000 1000000
*
* We'll default to the middle level that both agree on */
* We'll default to the middle level that both agree on. Except we do it on a 2s window
* (i.e. 200ms per 2s, rather than 100ms per 1s), because that's the window duration the
* kernel will allow us to do unprivileged, also in the future. */
if (asprintf((char**) &write_buffer,
"%s " USEC_FMT " " USEC_FMT,
MEMORY_PRESSURE_DEFAULT_TYPE,

2
test/units/testsuite-79.sh
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@ -43,7 +43,7 @@ test -w "$MEMORY_PRESSURE_WATCH"
ls -al "$MEMORY_PRESSURE_WATCH"
EXPECTED="$(echo -n -e "some 123000 1000000\x00" | base64)"
EXPECTED="$(echo -n -e "some 123000 2000000\x00" | base64)"
test "$EXPECTED" = "$MEMORY_PRESSURE_WRITE"