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From f45cb6d6a2c247c7594d9965cbb745303adb61d6 Mon Sep 17 00:00:00 2001
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From: Chris Down <chris@chrisdown.name>
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Date: Thu, 28 Mar 2019 12:50:50 +0000
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Subject: [PATCH] cgroup: Implement default propagation of MemoryLow with
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 DefaultMemoryLow
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In cgroup v2 we have protection tunables -- currently MemoryLow and
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MemoryMin (there will be more in future for other resources, too). The
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design of these protection tunables requires not only intermediate
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cgroups to propagate protections, but also the units at the leaf of that
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resource's operation to accept it (by setting MemoryLow or MemoryMin).
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This makes sense from an low-level API design perspective, but it's a
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good idea to also have a higher-level abstraction that can, by default,
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propagate these resources to children recursively. In this patch, this
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happens by having descendants set memory.low to N if their ancestor has
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DefaultMemoryLow=N -- assuming they don't set a separate MemoryLow
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value.
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Any affected unit can opt out of this propagation by manually setting
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`MemoryLow` to some value in its unit configuration. A unit can also
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stop further propagation by setting `DefaultMemoryLow=` with no
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argument. This removes further propagation in the subtree, but has no
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effect on the unit itself (for that, use `MemoryLow=0`).
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Our use case in production is simplifying the configuration of machines
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which heavily rely on memory protection tunables, but currently require
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tweaking a huge number of unit files to make that a reality. This
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directive makes that significantly less fragile, and decreases the risk
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of misconfiguration.
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After this patch is merged, I will implement DefaultMemoryMin= using the
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same principles.
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(cherry picked from commit c52db42b78f6fbeb7792cc4eca27e2767a48b6ca)
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Related: #1763435
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---
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 doc/TRANSIENT-SETTINGS.md             |   1 +
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 man/systemd.resource-control.xml      |   4 +
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 src/core/cgroup.c                     |  58 +++++++++--
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 src/core/cgroup.h                     |   6 ++
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 src/core/dbus-cgroup.c                |   7 ++
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 src/core/load-fragment-gperf.gperf.m4 |   1 +
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 src/core/load-fragment.c              |  13 ++-
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 src/shared/bus-unit-util.c            |   2 +-
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 src/shared/bus-util.c                 |   2 +-
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 src/systemctl/systemctl.c             |   3 +
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 src/test/meson.build                  |   6 ++
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 src/test/test-cgroup-unit-default.c   | 145 ++++++++++++++++++++++++++
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 test/dml-discard-empty.service        |   7 ++
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 test/dml-discard-set-ml.service       |   8 ++
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 test/dml-discard.slice                |   5 +
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 test/dml-override-empty.service       |   7 ++
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 test/dml-override.slice               |   5 +
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 test/dml-passthrough-empty.service    |   7 ++
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 test/dml-passthrough-set-dml.service  |   8 ++
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 test/dml-passthrough-set-ml.service   |   8 ++
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 test/dml-passthrough.slice            |   5 +
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 test/dml.slice                        |   5 +
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 test/meson.build                      |  10 ++
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 23 files changed, 310 insertions(+), 13 deletions(-)
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 create mode 100644 src/test/test-cgroup-unit-default.c
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 create mode 100644 test/dml-discard-empty.service
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 create mode 100644 test/dml-discard-set-ml.service
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 create mode 100644 test/dml-discard.slice
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 create mode 100644 test/dml-override-empty.service
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 create mode 100644 test/dml-override.slice
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 create mode 100644 test/dml-passthrough-empty.service
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 create mode 100644 test/dml-passthrough-set-dml.service
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 create mode 100644 test/dml-passthrough-set-ml.service
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 create mode 100644 test/dml-passthrough.slice
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 create mode 100644 test/dml.slice
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diff --git a/doc/TRANSIENT-SETTINGS.md b/doc/TRANSIENT-SETTINGS.md
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index 93865c0333..5a8fa0727e 100644
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--- a/doc/TRANSIENT-SETTINGS.md
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+++ b/doc/TRANSIENT-SETTINGS.md
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@@ -223,6 +223,7 @@ All cgroup/resource control settings are available for transient units
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 ✓ AllowedMemoryNodes=
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 ✓ MemoryAccounting=
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 ✓ MemoryMin=
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+✓ DefaultMemoryLow=
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 ✓ MemoryLow=
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 ✓ MemoryHigh=
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 ✓ MemoryMax=
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diff --git a/man/systemd.resource-control.xml b/man/systemd.resource-control.xml
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index 63a0c87565..27f16001dd 100644
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--- a/man/systemd.resource-control.xml
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+++ b/man/systemd.resource-control.xml
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@@ -305,6 +305,10 @@
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           <para>This setting is supported only if the unified control group hierarchy is used and disables
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           <varname>MemoryLimit=</varname>.</para>
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+
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+          <para>Units may can have their children use a default <literal>memory.low</literal> value by specifying
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+          <varname>DefaultMemoryLow=</varname>, which has the same usage as <varname>MemoryLow=</varname>. This setting
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+          does not affect <literal>memory.low</literal> in the unit itself.</para>
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         </listitem>
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       </varlistentry>
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diff --git a/src/core/cgroup.c b/src/core/cgroup.c
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index a17b38f914..f804bf4727 100644
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--- a/src/core/cgroup.c
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+++ b/src/core/cgroup.c
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@@ -220,6 +220,7 @@ void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix) {
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                 "%sStartupIOWeight=%" PRIu64 "\n"
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                 "%sBlockIOWeight=%" PRIu64 "\n"
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                 "%sStartupBlockIOWeight=%" PRIu64 "\n"
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+                "%sDefaultMemoryLow=%" PRIu64 "\n"
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                 "%sMemoryMin=%" PRIu64 "\n"
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                 "%sMemoryLow=%" PRIu64 "\n"
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                 "%sMemoryHigh=%" PRIu64 "\n"
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@@ -247,6 +248,7 @@ void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix) {
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                 prefix, c->startup_io_weight,
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                 prefix, c->blockio_weight,
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                 prefix, c->startup_blockio_weight,
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+                prefix, c->default_memory_low,
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                 prefix, c->memory_min,
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                 prefix, c->memory_low,
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                 prefix, c->memory_high,
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@@ -370,6 +372,32 @@ int cgroup_add_device_allow(CGroupContext *c, const char *dev, const char *mode)
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         return 0;
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 }
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+uint64_t unit_get_ancestor_memory_low(Unit *u) {
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+        CGroupContext *c;
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+
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+        /* 1. Is MemoryLow set in this unit? If so, use that.
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+         * 2. Is DefaultMemoryLow set in any ancestor? If so, use that.
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+         * 3. Otherwise, return CGROUP_LIMIT_MIN. */
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+
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+        assert(u);
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+
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+        c = unit_get_cgroup_context(u);
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+
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+        if (c->memory_low_set)
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+                return c->memory_low;
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+
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+        while (UNIT_ISSET(u->slice)) {
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+                u = UNIT_DEREF(u->slice);
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+                c = unit_get_cgroup_context(u);
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+
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+                if (c->default_memory_low_set)
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+                        return c->default_memory_low;
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+        }
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+
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+        /* We've reached the root, but nobody had DefaultMemoryLow set, so set it to the kernel default. */
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+        return CGROUP_LIMIT_MIN;
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+}
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+
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 static int lookup_block_device(const char *p, dev_t *ret) {
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         struct stat st;
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         int r;
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@@ -807,8 +835,17 @@ static void cgroup_apply_blkio_device_limit(Unit *u, const char *dev_path, uint6
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                               "Failed to set blkio.throttle.write_bps_device: %m");
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 }
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-static bool cgroup_context_has_unified_memory_config(CGroupContext *c) {
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-        return c->memory_min > 0 || c->memory_low > 0 || c->memory_high != CGROUP_LIMIT_MAX || c->memory_max != CGROUP_LIMIT_MAX || c->memory_swap_max != CGROUP_LIMIT_MAX;
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+static bool unit_has_unified_memory_config(Unit *u) {
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+        CGroupContext *c;
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+
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+        assert(u);
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+
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+        c = unit_get_cgroup_context(u);
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+        assert(c);
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+
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+        return c->memory_min > 0 || unit_get_ancestor_memory_low(u) > 0 ||
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+               c->memory_high != CGROUP_LIMIT_MAX || c->memory_max != CGROUP_LIMIT_MAX ||
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+               c->memory_swap_max != CGROUP_LIMIT_MAX;
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 }
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 static void cgroup_apply_unified_memory_limit(Unit *u, const char *file, uint64_t v) {
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@@ -1056,7 +1093,7 @@ static void cgroup_context_apply(
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                 if (cg_all_unified() > 0) {
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                         uint64_t max, swap_max = CGROUP_LIMIT_MAX;
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-                        if (cgroup_context_has_unified_memory_config(c)) {
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+                        if (unit_has_unified_memory_config(u)) {
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                                 max = c->memory_max;
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                                 swap_max = c->memory_swap_max;
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                         } else {
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@@ -1067,7 +1104,7 @@ static void cgroup_context_apply(
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                         }
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                         cgroup_apply_unified_memory_limit(u, "memory.min", c->memory_min);
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-                        cgroup_apply_unified_memory_limit(u, "memory.low", c->memory_low);
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+                        cgroup_apply_unified_memory_limit(u, "memory.low", unit_get_ancestor_memory_low(u));
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                         cgroup_apply_unified_memory_limit(u, "memory.high", c->memory_high);
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                         cgroup_apply_unified_memory_limit(u, "memory.max", max);
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                         cgroup_apply_unified_memory_limit(u, "memory.swap.max", swap_max);
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@@ -1075,7 +1112,7 @@ static void cgroup_context_apply(
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                         char buf[DECIMAL_STR_MAX(uint64_t) + 1];
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                         uint64_t val;
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-                        if (cgroup_context_has_unified_memory_config(c)) {
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+                        if (unit_has_unified_memory_config(u)) {
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                                 val = c->memory_max;
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                                 log_cgroup_compat(u, "Applying MemoryMax %" PRIi64 " as MemoryLimit", val);
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                         } else
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@@ -1204,8 +1241,13 @@ static void cgroup_context_apply(
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                 cgroup_apply_firewall(u);
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 }
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-CGroupMask cgroup_context_get_mask(CGroupContext *c) {
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+static CGroupMask unit_get_cgroup_mask(Unit *u) {
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         CGroupMask mask = 0;
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+        CGroupContext *c;
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+
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+        assert(u);
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+
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+        c = unit_get_cgroup_context(u);
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         /* Figure out which controllers we need */
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@@ -1223,7 +1265,7 @@ CGroupMask cgroup_context_get_mask(CGroupContext *c) {
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         if (c->memory_accounting ||
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             c->memory_limit != CGROUP_LIMIT_MAX ||
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-            cgroup_context_has_unified_memory_config(c))
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+            unit_has_unified_memory_config(u))
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                 mask |= CGROUP_MASK_MEMORY;
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         if (c->device_allow ||
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@@ -1246,7 +1288,7 @@ CGroupMask unit_get_own_mask(Unit *u) {
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         if (!c)
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                 return 0;
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-        return cgroup_context_get_mask(c) | unit_get_delegate_mask(u);
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+        return unit_get_cgroup_mask(u) | unit_get_delegate_mask(u);
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 }
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 CGroupMask unit_get_delegate_mask(Unit *u) {
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diff --git a/src/core/cgroup.h b/src/core/cgroup.h
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index 8102b442b8..a263d6a169 100644
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--- a/src/core/cgroup.h
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+++ b/src/core/cgroup.h
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@@ -95,12 +95,16 @@ struct CGroupContext {
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         LIST_HEAD(CGroupIODeviceLimit, io_device_limits);
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         LIST_HEAD(CGroupIODeviceLatency, io_device_latencies);
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+        uint64_t default_memory_low;
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         uint64_t memory_min;
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         uint64_t memory_low;
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         uint64_t memory_high;
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         uint64_t memory_max;
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         uint64_t memory_swap_max;
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+        bool default_memory_low_set;
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+        bool memory_low_set;
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+
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         LIST_HEAD(IPAddressAccessItem, ip_address_allow);
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         LIST_HEAD(IPAddressAccessItem, ip_address_deny);
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@@ -191,6 +195,8 @@ Unit *manager_get_unit_by_cgroup(Manager *m, const char *cgroup);
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 Unit *manager_get_unit_by_pid_cgroup(Manager *m, pid_t pid);
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 Unit* manager_get_unit_by_pid(Manager *m, pid_t pid);
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+uint64_t unit_get_ancestor_memory_low(Unit *u);
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+
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 int unit_search_main_pid(Unit *u, pid_t *ret);
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 int unit_watch_all_pids(Unit *u);
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diff --git a/src/core/dbus-cgroup.c b/src/core/dbus-cgroup.c
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index 6ce5984a02..2115d43b0c 100644
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--- a/src/core/dbus-cgroup.c
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+++ b/src/core/dbus-cgroup.c
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@@ -353,6 +353,7 @@ const sd_bus_vtable bus_cgroup_vtable[] = {
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         SD_BUS_PROPERTY("BlockIOReadBandwidth", "a(st)", property_get_blockio_device_bandwidths, 0, 0),
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         SD_BUS_PROPERTY("BlockIOWriteBandwidth", "a(st)", property_get_blockio_device_bandwidths, 0, 0),
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         SD_BUS_PROPERTY("MemoryAccounting", "b", bus_property_get_bool, offsetof(CGroupContext, memory_accounting), 0),
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+        SD_BUS_PROPERTY("DefaultMemoryLow", "t", NULL, offsetof(CGroupContext, default_memory_low), 0),
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         SD_BUS_PROPERTY("MemoryMin", "t", NULL, offsetof(CGroupContext, memory_min), 0),
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         SD_BUS_PROPERTY("MemoryLow", "t", NULL, offsetof(CGroupContext, memory_low), 0),
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         SD_BUS_PROPERTY("MemoryHigh", "t", NULL, offsetof(CGroupContext, memory_high), 0),
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@@ -668,6 +669,9 @@ int bus_cgroup_set_property(
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         if (streq(name, "MemoryLow"))
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                 return bus_cgroup_set_memory(u, name, &c->memory_low, message, flags, error);
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+        if (streq(name, "DefaultMemoryLow"))
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+                return bus_cgroup_set_memory(u, name, &c->default_memory_low, message, flags, error);
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+
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         if (streq(name, "MemoryHigh"))
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                 return bus_cgroup_set_memory(u, name, &c->memory_high, message, flags, error);
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@@ -686,6 +690,9 @@ int bus_cgroup_set_property(
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         if (streq(name, "MemoryLowScale"))
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                 return bus_cgroup_set_memory_scale(u, name, &c->memory_low, message, flags, error);
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+        if (streq(name, "DefaultMemoryLowScale"))
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+                return bus_cgroup_set_memory_scale(u, name, &c->default_memory_low, message, flags, error);
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+
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         if (streq(name, "MemoryHighScale"))
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                 return bus_cgroup_set_memory_scale(u, name, &c->memory_high, message, flags, error);
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diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
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index 1c6e539f30..43cc78fdea 100644
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--- a/src/core/load-fragment-gperf.gperf.m4
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+++ b/src/core/load-fragment-gperf.gperf.m4
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@@ -172,6 +172,7 @@ $1.CPUQuota,                     config_parse_cpu_quota,             0,
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 $1.CPUQuotaPeriodSec,            config_parse_sec_def_infinity,      0,                             offsetof($1, cgroup_context.cpu_quota_period_usec)
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 $1.MemoryAccounting,             config_parse_bool,                  0,                             offsetof($1, cgroup_context.memory_accounting)
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 $1.MemoryMin,                    config_parse_memory_limit,          0,                             offsetof($1, cgroup_context)
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+$1.DefaultMemoryLow,             config_parse_memory_limit,          0,                             offsetof($1, cgroup_context)
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 $1.MemoryLow,                    config_parse_memory_limit,          0,                             offsetof($1, cgroup_context)
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 $1.MemoryHigh,                   config_parse_memory_limit,          0,                             offsetof($1, cgroup_context)
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 $1.MemoryMax,                    config_parse_memory_limit,          0,                             offsetof($1, cgroup_context)
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diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
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index 89a3457acc..20faed02ad 100644
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--- a/src/core/load-fragment.c
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+++ b/src/core/load-fragment.c
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@@ -3096,11 +3096,18 @@ int config_parse_memory_limit(
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                 }
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         }
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-        if (streq(lvalue, "MemoryMin"))
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+        if (streq(lvalue, "DefaultMemoryLow")) {
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+                c->default_memory_low_set = true;
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+                if (isempty(rvalue))
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+                        c->default_memory_low = CGROUP_LIMIT_MIN;
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+                else
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+                        c->default_memory_low = bytes;
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+        } else if (streq(lvalue, "MemoryMin"))
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                 c->memory_min = bytes;
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-        else if (streq(lvalue, "MemoryLow"))
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+        else if (streq(lvalue, "MemoryLow")) {
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                 c->memory_low = bytes;
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-        else if (streq(lvalue, "MemoryHigh"))
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+                c->memory_low_set = true;
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+        } else if (streq(lvalue, "MemoryHigh"))
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                 c->memory_high = bytes;
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         else if (streq(lvalue, "MemoryMax"))
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                 c->memory_max = bytes;
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diff --git a/src/shared/bus-unit-util.c b/src/shared/bus-unit-util.c
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index 203c068d02..f88730a85d 100644
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--- a/src/shared/bus-unit-util.c
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+++ b/src/shared/bus-unit-util.c
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@@ -429,7 +429,7 @@ static int bus_append_cgroup_property(sd_bus_message *m, const char *field, cons
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                 return 1;
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         }
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-        if (STR_IN_SET(field, "MemoryMin", "MemoryLow", "MemoryHigh", "MemoryMax", "MemorySwapMax", "MemoryLimit", "TasksMax")) {
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+        if (STR_IN_SET(field, "MemoryMin", "DefaultMemoryLow", "MemoryLow", "MemoryHigh", "MemoryMax", "MemorySwapMax", "MemoryLimit", "TasksMax")) {
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                 if (isempty(eq) || streq(eq, "infinity")) {
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                         r = sd_bus_message_append(m, "(sv)", field, "t", CGROUP_LIMIT_MAX);
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diff --git a/src/shared/bus-util.c b/src/shared/bus-util.c
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index 5ed68429be..0ba2712deb 100644
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--- a/src/shared/bus-util.c
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+++ b/src/shared/bus-util.c
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@@ -774,7 +774,7 @@ int bus_print_property(const char *name, sd_bus_message *m, bool value, bool all
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                         print_property(name, "%s", "[not set]");
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-                else if ((STR_IN_SET(name, "MemoryLow", "MemoryHigh", "MemoryMax", "MemorySwapMax", "MemoryLimit") && u == CGROUP_LIMIT_MAX) ||
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+                else if ((STR_IN_SET(name, "DefaultMemoryLow", "MemoryLow", "MemoryHigh", "MemoryMax", "MemorySwapMax", "MemoryLimit") && u == CGROUP_LIMIT_MAX) ||
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                          (STR_IN_SET(name, "TasksMax", "DefaultTasksMax") && u == (uint64_t) -1) ||
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                          (startswith(name, "Limit") && u == (uint64_t) -1) ||
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                          (startswith(name, "DefaultLimit") && u == (uint64_t) -1))
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diff --git a/src/systemctl/systemctl.c b/src/systemctl/systemctl.c
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index 35ad20f510..763ca0c6b7 100644
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--- a/src/systemctl/systemctl.c
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+++ b/src/systemctl/systemctl.c
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@@ -3918,6 +3918,8 @@ typedef struct UnitStatusInfo {
4cad4c
         uint64_t ip_ingress_bytes;
4cad4c
         uint64_t ip_egress_bytes;
4cad4c
 
4cad4c
+        uint64_t default_memory_low;
4cad4c
+
4cad4c
         LIST_HEAD(ExecStatusInfo, exec);
4cad4c
 } UnitStatusInfo;
4cad4c
 
4cad4c
@@ -5028,6 +5030,7 @@ static int show_one(
4cad4c
                 { "Where",                          "s",              NULL,           offsetof(UnitStatusInfo, where)                             },
4cad4c
                 { "What",                           "s",              NULL,           offsetof(UnitStatusInfo, what)                              },
4cad4c
                 { "MemoryCurrent",                  "t",              NULL,           offsetof(UnitStatusInfo, memory_current)                    },
4cad4c
+                { "DefaultMemoryLow",               "t",              NULL,           offsetof(UnitStatusInfo, default_memory_low)                },
4cad4c
                 { "MemoryMin",                      "t",              NULL,           offsetof(UnitStatusInfo, memory_min)                        },
4cad4c
                 { "MemoryLow",                      "t",              NULL,           offsetof(UnitStatusInfo, memory_low)                        },
4cad4c
                 { "MemoryHigh",                     "t",              NULL,           offsetof(UnitStatusInfo, memory_high)                       },
4cad4c
diff --git a/src/test/meson.build b/src/test/meson.build
4cad4c
index 22264d034c..7b310d4ec7 100644
4cad4c
--- a/src/test/meson.build
4cad4c
+++ b/src/test/meson.build
4cad4c
@@ -518,6 +518,12 @@ tests += [
4cad4c
           libshared],
4cad4c
          []],
4cad4c
 
4cad4c
+        [['src/test/test-cgroup-unit-default.c',
4cad4c
+          'src/test/test-helper.c'],
4cad4c
+         [libcore,
4cad4c
+          libshared],
4cad4c
+         []],
4cad4c
+
4cad4c
         [['src/test/test-cgroup-mask.c',
4cad4c
           'src/test/test-helper.c'],
4cad4c
          [libcore,
4cad4c
diff --git a/src/test/test-cgroup-unit-default.c b/src/test/test-cgroup-unit-default.c
4cad4c
new file mode 100644
4cad4c
index 0000000000..54f7d50c45
4cad4c
--- /dev/null
4cad4c
+++ b/src/test/test-cgroup-unit-default.c
4cad4c
@@ -0,0 +1,145 @@
4cad4c
+/* SPDX-License-Identifier: LGPL-2.1+ */
4cad4c
+
4cad4c
+#include <stdio.h>
4cad4c
+
4cad4c
+#include "cgroup.h"
4cad4c
+#include "manager.h"
4cad4c
+#include "rm-rf.h"
4cad4c
+#include "test-helper.h"
4cad4c
+#include "tests.h"
4cad4c
+#include "unit.h"
4cad4c
+
4cad4c
+static int test_default_memory_low(void) {
4cad4c
+        _cleanup_(rm_rf_physical_and_freep) char *runtime_dir = NULL;
4cad4c
+        _cleanup_(manager_freep) Manager *m = NULL;
4cad4c
+        Unit *root, *dml,
4cad4c
+             *dml_passthrough, *dml_passthrough_empty, *dml_passthrough_set_dml, *dml_passthrough_set_ml,
4cad4c
+             *dml_override, *dml_override_empty,
4cad4c
+             *dml_discard, *dml_discard_empty, *dml_discard_set_ml;
4cad4c
+        uint64_t dml_tree_default;
4cad4c
+        int r;
4cad4c
+
4cad4c
+        r = enter_cgroup_subroot();
4cad4c
+        if (r == -ENOMEDIUM)
4cad4c
+                return EXIT_TEST_SKIP;
4cad4c
+
4cad4c
+        assert_se(set_unit_path(get_testdata_dir()) >= 0);
4cad4c
+        assert_se(runtime_dir = setup_fake_runtime_dir());
4cad4c
+        r = manager_new(UNIT_FILE_USER, MANAGER_TEST_RUN_BASIC, &m);
4cad4c
+        if (IN_SET(r, -EPERM, -EACCES)) {
4cad4c
+                log_error_errno(r, "manager_new: %m");
4cad4c
+                return EXIT_TEST_SKIP;
4cad4c
+        }
4cad4c
+
4cad4c
+        assert_se(r >= 0);
4cad4c
+        assert_se(manager_startup(m, NULL, NULL) >= 0);
4cad4c
+
4cad4c
+        /* dml.slice has DefaultMemoryLow=50. Beyond that, individual subhierarchies look like this:
4cad4c
+         *
4cad4c
+         * 1. dml-passthrough.slice sets MemoryLow=100. This should not affect its children, as only
4cad4c
+         *    DefaultMemoryLow is propagated, not MemoryLow. As such, all leaf services should end up with
4cad4c
+         *    memory.low as 50, inherited from dml.slice, *except* for dml-passthrough-set-ml.service, which
4cad4c
+         *    should have the value of 25, as it has MemoryLow explicitly set.
4cad4c
+         *
4cad4c
+         *                                                  ┌───────────┐
4cad4c
+         *                                                  │ dml.slice │
4cad4c
+         *                                                  └─────┬─────┘
4cad4c
+         *                                                  MemoryLow=100
4cad4c
+         *                                            ┌───────────┴───────────┐
4cad4c
+         *                                            │ dml-passthrough.slice │
4cad4c
+         *                                            └───────────┬───────────┘
4cad4c
+         *                    ┌───────────────────────────────────┼───────────────────────────────────┐
4cad4c
+         *             no new settings                   DefaultMemoryLow=15                     MemoryLow=25
4cad4c
+         *    ┌───────────────┴───────────────┐  ┌────────────────┴────────────────┐  ┌───────────────┴────────────────┐
4cad4c
+         *    │ dml-passthrough-empty.service │  │ dml-passthrough-set-dml.service │  │ dml-passthrough-set-ml.service │
4cad4c
+         *    └───────────────────────────────┘  └─────────────────────────────────┘  └────────────────────────────────┘
4cad4c
+         *
4cad4c
+         * 2. dml-override.slice sets DefaultMemoryLow=10. As such, dml-override-empty.service should also
4cad4c
+         *    end up with a memory.low of 10. dml-override.slice should still have a memory.low of 50.
4cad4c
+         *
4cad4c
+         *            ┌───────────┐
4cad4c
+         *            │ dml.slice │
4cad4c
+         *            └─────┬─────┘
4cad4c
+         *         DefaultMemoryLow=10
4cad4c
+         *        ┌─────────┴──────────┐
4cad4c
+         *        │ dml-override.slice │
4cad4c
+         *        └─────────┬──────────┘
4cad4c
+         *           no new settings
4cad4c
+         *    ┌─────────────┴──────────────┐
4cad4c
+         *    │ dml-override-empty.service │
4cad4c
+         *    └────────────────────────────┘
4cad4c
+         *
4cad4c
+         * 3. dml-discard.slice sets DefaultMemoryLow= with no rvalue. As such,
4cad4c
+         *    dml-discard-empty.service should end up with a value of 0.
4cad4c
+         *    dml-discard-explicit-ml.service sets MemoryLow=70, and as such should have that override the
4cad4c
+         *    reset DefaultMemoryLow value. dml-discard.slice should still have an eventual memory.low of 50.
4cad4c
+         *
4cad4c
+         *                           ┌───────────┐
4cad4c
+         *                           │ dml.slice │
4cad4c
+         *                           └─────┬─────┘
4cad4c
+         *                         DefaultMemoryLow=
4cad4c
+         *                       ┌─────────┴─────────┐
4cad4c
+         *                       │ dml-discard.slice │
4cad4c
+         *                       └─────────┬─────────┘
4cad4c
+         *                  ┌──────────────┴───────────────┐
4cad4c
+         *           no new settings                  MemoryLow=15
4cad4c
+         *    ┌─────────────┴─────────────┐  ┌─────────────┴──────────────┐
4cad4c
+         *    │ dml-discard-empty.service │  │ dml-discard-set-ml.service │
4cad4c
+         *    └───────────────────────────┘  └────────────────────────────┘
4cad4c
+         */
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml.slice", NULL, &dml) >= 0);
4cad4c
+
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-passthrough.slice", NULL, &dml_passthrough) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_passthrough->slice) == dml);
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-passthrough-empty.service", NULL, &dml_passthrough_empty) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_passthrough_empty->slice) == dml_passthrough);
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-passthrough-set-dml.service", NULL, &dml_passthrough_set_dml) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_passthrough_set_dml->slice) == dml_passthrough);
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-passthrough-set-ml.service", NULL, &dml_passthrough_set_ml) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_passthrough_set_ml->slice) == dml_passthrough);
4cad4c
+
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-override.slice", NULL, &dml_override) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_override->slice) == dml);
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-override-empty.service", NULL, &dml_override_empty) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_override_empty->slice) == dml_override);
4cad4c
+
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-discard.slice", NULL, &dml_discard) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_discard->slice) == dml);
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-discard-empty.service", NULL, &dml_discard_empty) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_discard_empty->slice) == dml_discard);
4cad4c
+        assert_se(manager_load_startable_unit_or_warn(m, "dml-discard-set-ml.service", NULL, &dml_discard_set_ml) >= 0);
4cad4c
+        assert_se(UNIT_DEREF(dml_discard_set_ml->slice) == dml_discard);
4cad4c
+
4cad4c
+        root = UNIT_DEREF(dml->slice);
4cad4c
+        assert_se(!UNIT_ISSET(root->slice));
4cad4c
+
4cad4c
+        assert_se(unit_get_ancestor_memory_low(root) == CGROUP_LIMIT_MIN);
4cad4c
+
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml) == CGROUP_LIMIT_MIN);
4cad4c
+        dml_tree_default = unit_get_cgroup_context(dml)->default_memory_low;
4cad4c
+        assert_se(dml_tree_default == 50);
4cad4c
+
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_passthrough) == 100);
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_passthrough_empty) == dml_tree_default);
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_passthrough_set_dml) == 50);
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_passthrough_set_ml) == 25);
4cad4c
+
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_override) == dml_tree_default);
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_override_empty) == 10);
4cad4c
+
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_discard) == dml_tree_default);
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_discard_empty) == CGROUP_LIMIT_MIN);
4cad4c
+        assert_se(unit_get_ancestor_memory_low(dml_discard_set_ml) == 15);
4cad4c
+
4cad4c
+        return 0;
4cad4c
+}
4cad4c
+
4cad4c
+int main(int argc, char* argv[]) {
4cad4c
+        int rc = EXIT_SUCCESS;
4cad4c
+
4cad4c
+        test_setup_logging(LOG_DEBUG);
4cad4c
+
4cad4c
+        TEST_REQ_RUNNING_SYSTEMD(rc = test_default_memory_low());
4cad4c
+
4cad4c
+        return rc;
4cad4c
+}
4cad4c
diff --git a/test/dml-discard-empty.service b/test/dml-discard-empty.service
4cad4c
new file mode 100644
4cad4c
index 0000000000..75228f6470
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-discard-empty.service
4cad4c
@@ -0,0 +1,7 @@
4cad4c
+[Unit]
4cad4c
+Description=DML discard empty service
4cad4c
+
4cad4c
+[Service]
4cad4c
+Slice=dml-discard.slice
4cad4c
+Type=oneshot
4cad4c
+ExecStart=/bin/true
4cad4c
diff --git a/test/dml-discard-set-ml.service b/test/dml-discard-set-ml.service
4cad4c
new file mode 100644
4cad4c
index 0000000000..591c99270c
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-discard-set-ml.service
4cad4c
@@ -0,0 +1,8 @@
4cad4c
+[Unit]
4cad4c
+Description=DML discard set ml service
4cad4c
+
4cad4c
+[Service]
4cad4c
+Slice=dml-discard.slice
4cad4c
+Type=oneshot
4cad4c
+ExecStart=/bin/true
4cad4c
+MemoryLow=15
4cad4c
diff --git a/test/dml-discard.slice b/test/dml-discard.slice
4cad4c
new file mode 100644
4cad4c
index 0000000000..e26d86846c
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-discard.slice
4cad4c
@@ -0,0 +1,5 @@
4cad4c
+[Unit]
4cad4c
+Description=DML discard slice
4cad4c
+
4cad4c
+[Slice]
4cad4c
+DefaultMemoryLow=
4cad4c
diff --git a/test/dml-override-empty.service b/test/dml-override-empty.service
4cad4c
new file mode 100644
4cad4c
index 0000000000..142c98720c
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-override-empty.service
4cad4c
@@ -0,0 +1,7 @@
4cad4c
+[Unit]
4cad4c
+Description=DML override empty service
4cad4c
+
4cad4c
+[Service]
4cad4c
+Slice=dml-override.slice
4cad4c
+Type=oneshot
4cad4c
+ExecStart=/bin/true
4cad4c
diff --git a/test/dml-override.slice b/test/dml-override.slice
4cad4c
new file mode 100644
4cad4c
index 0000000000..feb6773e39
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-override.slice
4cad4c
@@ -0,0 +1,5 @@
4cad4c
+[Unit]
4cad4c
+Description=DML override slice
4cad4c
+
4cad4c
+[Slice]
4cad4c
+DefaultMemoryLow=10
4cad4c
diff --git a/test/dml-passthrough-empty.service b/test/dml-passthrough-empty.service
4cad4c
new file mode 100644
4cad4c
index 0000000000..34832de491
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-passthrough-empty.service
4cad4c
@@ -0,0 +1,7 @@
4cad4c
+[Unit]
4cad4c
+Description=DML passthrough empty service
4cad4c
+
4cad4c
+[Service]
4cad4c
+Slice=dml-passthrough.slice
4cad4c
+Type=oneshot
4cad4c
+ExecStart=/bin/true
4cad4c
diff --git a/test/dml-passthrough-set-dml.service b/test/dml-passthrough-set-dml.service
4cad4c
new file mode 100644
4cad4c
index 0000000000..5bdf4ed4b7
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-passthrough-set-dml.service
4cad4c
@@ -0,0 +1,8 @@
4cad4c
+[Unit]
4cad4c
+Description=DML passthrough set DML service
4cad4c
+
4cad4c
+[Service]
4cad4c
+Slice=dml-passthrough.slice
4cad4c
+Type=oneshot
4cad4c
+ExecStart=/bin/true
4cad4c
+DefaultMemoryLow=15
4cad4c
diff --git a/test/dml-passthrough-set-ml.service b/test/dml-passthrough-set-ml.service
4cad4c
new file mode 100644
4cad4c
index 0000000000..2abd591389
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-passthrough-set-ml.service
4cad4c
@@ -0,0 +1,8 @@
4cad4c
+[Unit]
4cad4c
+Description=DML passthrough set ML service
4cad4c
+
4cad4c
+[Service]
4cad4c
+Slice=dml-passthrough.slice
4cad4c
+Type=oneshot
4cad4c
+ExecStart=/bin/true
4cad4c
+MemoryLow=25
4cad4c
diff --git a/test/dml-passthrough.slice b/test/dml-passthrough.slice
4cad4c
new file mode 100644
4cad4c
index 0000000000..1b1a848edb
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml-passthrough.slice
4cad4c
@@ -0,0 +1,5 @@
4cad4c
+[Unit]
4cad4c
+Description=DML passthrough slice
4cad4c
+
4cad4c
+[Slice]
4cad4c
+MemoryLow=100
4cad4c
diff --git a/test/dml.slice b/test/dml.slice
4cad4c
new file mode 100644
4cad4c
index 0000000000..84e333ef04
4cad4c
--- /dev/null
4cad4c
+++ b/test/dml.slice
4cad4c
@@ -0,0 +1,5 @@
4cad4c
+[Unit]
4cad4c
+Description=DML slice
4cad4c
+
4cad4c
+[Slice]
4cad4c
+DefaultMemoryLow=50
4cad4c
diff --git a/test/meson.build b/test/meson.build
4cad4c
index 070731c4a9..52e4fa2e3c 100644
4cad4c
--- a/test/meson.build
4cad4c
+++ b/test/meson.build
4cad4c
@@ -7,6 +7,16 @@ test_data_files = '''
4cad4c
         c.service
4cad4c
         d.service
4cad4c
         daughter.service
4cad4c
+        dml.slice
4cad4c
+        dml-passthrough.slice
4cad4c
+        dml-passthrough-empty.service
4cad4c
+        dml-passthrough-set-dml.service
4cad4c
+        dml-passthrough-set-ml.service
4cad4c
+        dml-override.slice
4cad4c
+        dml-override-empty.service
4cad4c
+        dml-discard.slice
4cad4c
+        dml-discard-empty.service
4cad4c
+        dml-discard-set-ml.service
4cad4c
         e.service
4cad4c
         end.service
4cad4c
         f.service