cgroup: add support for memory.swap.current

In systemctl-show we only show current swap if ever swapped or non-zero. This
reduces the noise on swapless systems, that would otherwise always show a swap
value that never has the chance to become non-zero. It further reduces the
noise for services that never swapped.

src/core/cgroup.c

@@ -4047,6 +4047,9 @@ static int unit_get_memory_attr_raw(Unit *u, const char* mem_attribute, uint64_t
         assert(mem_attribute);
         assert(ret);
 
+        if (!UNIT_CGROUP_BOOL(u, memory_accounting))
+                return -ENODATA;
+
         if (!u->cgroup_path)
                 return -ENODATA;
 
@@ -4100,6 +4103,10 @@ int unit_get_memory_peak(Unit *u, uint64_t *ret) {
         return unit_get_memory_attr_cached(u, "memory.peak", &u->memory_peak_last, ret);
 }
 
+int unit_get_memory_swap_current(Unit *u, uint64_t *ret) {
+        return unit_get_memory_attr_raw(u, "memory.swap.current", ret);
+}
+
 int unit_get_memory_swap_peak(Unit *u, uint64_t *ret) {
         return unit_get_memory_attr_cached(u, "memory.swap.peak", &u->memory_swap_peak_last, ret);
 }

src/core/cgroup.h

@@ -354,6 +354,7 @@ int unit_synthesize_cgroup_empty_event(Unit *u);
 
 int unit_get_memory_current(Unit *u, uint64_t *ret);
 int unit_get_memory_peak(Unit *u, uint64_t *ret);
+int unit_get_memory_swap_current(Unit *u, uint64_t *ret);
 int unit_get_memory_swap_peak(Unit *u, uint64_t *ret);
 int unit_get_memory_available(Unit *u, uint64_t *ret);
 int unit_get_tasks_current(Unit *u, uint64_t *ret);

src/core/dbus-unit.c

@@ -1103,6 +1103,29 @@ static int property_get_peak_memory(
         return sd_bus_message_append(reply, "t", sz);
 }
 
+static int property_get_current_swap_memory(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        uint64_t sz = UINT64_MAX;
+        Unit *u = ASSERT_PTR(userdata);
+        int r;
+
+        assert(bus);
+        assert(reply);
+
+        r = unit_get_memory_swap_current(u, &sz);
+        if (r < 0 && r != -ENODATA)
+                log_unit_warning_errno(u, r, "Failed to get memory.swap.current attribute: %m");
+
+        return sd_bus_message_append(reply, "t", sz);
+}
+
 static int property_get_peak_swap_memory(
                 sd_bus *bus,
                 const char *path,
@@ -1583,6 +1606,7 @@ const sd_bus_vtable bus_unit_cgroup_vtable[] = {
         SD_BUS_PROPERTY("ControlGroupId", "t", NULL, offsetof(Unit, cgroup_id), 0),
         SD_BUS_PROPERTY("MemoryCurrent", "t", property_get_current_memory, 0, 0),
         SD_BUS_PROPERTY("MemoryPeak", "t", property_get_peak_memory, 0, 0),
+        SD_BUS_PROPERTY("MemorySwapCurrent", "t", property_get_current_swap_memory, 0, 0),
         SD_BUS_PROPERTY("MemorySwapPeak", "t", property_get_peak_swap_memory, 0, 0),
         SD_BUS_PROPERTY("MemoryAvailable", "t", property_get_available_memory, 0, 0),
         SD_BUS_PROPERTY("CPUUsageNSec", "t", property_get_cpu_usage, 0, 0),

src/systemctl/systemctl-show.c

@@ -251,6 +251,7 @@ typedef struct UnitStatusInfo {
         /* CGroup */
         uint64_t memory_current;
         uint64_t memory_peak;
+        uint64_t memory_swap_current;
         uint64_t memory_swap_peak;
         uint64_t memory_min;
         uint64_t memory_low;
@@ -704,9 +705,11 @@ static void print_status_info(
         if (i->memory_current != UINT64_MAX) {
                 printf("     Memory: %s", FORMAT_BYTES(i->memory_current));
 
-                bool show_memory_swap_peak = !IN_SET(i->memory_swap_peak, 0, CGROUP_LIMIT_MAX);
+                /* Only show current swap if it ever was non-zero or is currently non-zero. In both cases
+                   memory_swap_peak will be non-zero (and not CGROUP_LIMIT_MAX). */
+                bool show_memory_swap = !IN_SET(i->memory_swap_peak, 0, CGROUP_LIMIT_MAX);
                 if (i->memory_peak != CGROUP_LIMIT_MAX ||
-                    show_memory_swap_peak ||
+                    show_memory_swap ||
                     i->memory_min > 0 ||
                     i->memory_low > 0 || i->startup_memory_low > 0 ||
                     i->memory_high != CGROUP_LIMIT_MAX || i->startup_memory_high != CGROUP_LIMIT_MAX ||
@@ -774,7 +777,11 @@ static void print_status_info(
                                 printf("%speak: %s", prefix, FORMAT_BYTES(i->memory_peak));
                                 prefix = " ";
                         }
-                        if (show_memory_swap_peak) {
+                        if (show_memory_swap) {
+                                printf("%sswap: %s", prefix, FORMAT_BYTES(i->memory_swap_current));
+                                prefix = " ";
+                        }
+                        if (show_memory_swap) {
                                 printf("%sswap peak: %s", prefix, FORMAT_BYTES(i->memory_swap_peak));
                                 prefix = " ";
                         }
@@ -2045,6 +2052,7 @@ static int show_one(
                 { "What",                           "s",               NULL,           offsetof(UnitStatusInfo, what)                              },
                 { "MemoryCurrent",                  "t",               NULL,           offsetof(UnitStatusInfo, memory_current)                    },
                 { "MemoryPeak",                     "t",               NULL,           offsetof(UnitStatusInfo, memory_peak)                       },
+                { "MemorySwapCurrent",              "t",               NULL,           offsetof(UnitStatusInfo, memory_swap_current)               },
                 { "MemorySwapPeak",                 "t",               NULL,           offsetof(UnitStatusInfo, memory_swap_peak)                  },
                 { "MemoryAvailable",                "t",               NULL,           offsetof(UnitStatusInfo, memory_available)                  },
                 { "DefaultMemoryMin",               "t",               NULL,           offsetof(UnitStatusInfo, default_memory_min)                },
@@ -2103,6 +2111,7 @@ static int show_one(
                 .startup_memory_zswap_max = CGROUP_LIMIT_MAX,
                 .memory_limit = CGROUP_LIMIT_MAX,
                 .memory_peak = CGROUP_LIMIT_MAX,
+                .memory_swap_current = CGROUP_LIMIT_MAX,
                 .memory_swap_peak = CGROUP_LIMIT_MAX,
                 .memory_available = CGROUP_LIMIT_MAX,
                 .cpu_usage_nsec = UINT64_MAX,