systemd-oomd: manager/daemon

meson.build

@@ -2662,6 +2662,17 @@ if conf.get('ENABLE_PSTORE') == 1
                 install_dir : rootlibexecdir)
 endif
 
+if conf.get('ENABLE_OOMD') == 1
+        executable('systemd-oomd',
+                   systemd_oomd_sources,
+                   include_directories : includes,
+                   link_with : [libshared],
+                   dependencies : [],
+                   install_rpath : rootlibexecdir,
+                   install : true,
+                   install_dir : rootlibexecdir)
+endif
+
 if conf.get('ENABLE_BINFMT') == 1
         public_programs += executable(
                 'systemd-binfmt',

src/oom/meson.build

@@ -1,8 +1,11 @@
 # SPDX-License-Identifier: LGPL-2.1+
 
 systemd_oomd_sources = files('''
+        oomd-manager.c
+        oomd-manager.h
         oomd-util.c
         oomd-util.h
+        oomd.c
 '''.split())
 
 if conf.get('ENABLE_OOMD') == 1
@@ -13,4 +16,7 @@ if conf.get('ENABLE_OOMD') == 1
                  [],
                  []]
         ]
+
+        install_data('oomd.conf',
+                     install_dir : pkgsysconfdir)
 endif

src/oom/oomd-manager.c

@@ -0,0 +1,466 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "cgroup-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "oomd-manager.h"
+#include "path-util.h"
+
+typedef struct ManagedOOMReply {
+        ManagedOOMMode mode;
+        char *path;
+        char *property;
+        unsigned limit;
+} ManagedOOMReply;
+
+static void managed_oom_reply_destroy(ManagedOOMReply *reply) {
+        assert(reply);
+        free(reply->path);
+        free(reply->property);
+}
+
+static int managed_oom_mode(const char *name, JsonVariant *v, JsonDispatchFlags flags, void *userdata) {
+        ManagedOOMMode *mode = userdata, m;
+        const char *s;
+
+        assert(mode);
+        assert_se(s = json_variant_string(v));
+
+        m = managed_oom_mode_from_string(s);
+        if (m < 0)
+                return json_log(v, flags, SYNTHETIC_ERRNO(EINVAL), "%s is not a valid ManagedOOMMode", s);
+
+        *mode = m;
+        return 0;
+}
+
+static int process_managed_oom_reply(
+                Varlink *link,
+                JsonVariant *parameters,
+                const char *error_id,
+                VarlinkReplyFlags flags,
+                void *userdata) {
+        JsonVariant *c, *cgroups;
+        Manager *m = userdata;
+        int r = 0;
+
+        assert(m);
+
+        static const JsonDispatch dispatch_table[] = {
+                { "mode",     JSON_VARIANT_STRING,   managed_oom_mode,       offsetof(ManagedOOMReply, mode),     JSON_MANDATORY },
+                { "path",     JSON_VARIANT_STRING,   json_dispatch_string,   offsetof(ManagedOOMReply, path),     JSON_MANDATORY },
+                { "property", JSON_VARIANT_STRING,   json_dispatch_string,   offsetof(ManagedOOMReply, property), JSON_MANDATORY },
+                { "limit",    JSON_VARIANT_UNSIGNED, json_dispatch_unsigned, offsetof(ManagedOOMReply, limit),    0 },
+                {},
+        };
+
+        if (error_id) {
+                r = -EIO;
+                log_debug("Error getting ManagedOOM cgroups: %s", error_id);
+                goto finish;
+        }
+
+        cgroups = json_variant_by_key(parameters, "cgroups");
+        if (!cgroups) {
+                r = -EINVAL;
+                goto finish;
+        }
+
+        /* Skip malformed elements and keep processing in case the others are good */
+        JSON_VARIANT_ARRAY_FOREACH(c, cgroups) {
+                _cleanup_(managed_oom_reply_destroy) ManagedOOMReply reply = {};
+                OomdCGroupContext *ctx;
+                Hashmap *monitor_hm;
+                loadavg_t limit;
+                int ret;
+
+                if (!json_variant_is_object(c))
+                        continue;
+
+                ret = json_dispatch(c, dispatch_table, NULL, 0, &reply);
+                if (ret == -ENOMEM) {
+                        r = ret;
+                        goto finish;
+                } else if (ret < 0)
+                        continue;
+
+                monitor_hm = streq(reply.property, "ManagedOOMSwap") ?
+                                m->monitored_swap_cgroup_contexts : m->monitored_mem_pressure_cgroup_contexts;
+
+                if (reply.mode == MANAGED_OOM_AUTO) {
+                        (void) oomd_cgroup_context_free(hashmap_remove(monitor_hm, reply.path));
+                        continue;
+                }
+
+                limit = m->default_mem_pressure_limit;
+
+                if (streq(reply.property, "ManagedOOMMemoryPressure")) {
+                        if (reply.limit > 100)
+                                continue;
+                        else if (reply.limit != 0) {
+                                ret = store_loadavg_fixed_point((unsigned long) reply.limit, 0, &limit);
+                                if (ret < 0)
+                                        continue;
+                        }
+                }
+
+                ret = oomd_insert_cgroup_context(NULL, monitor_hm, reply.path);
+                if (ret == -ENOMEM) {
+                        r = ret;
+                        goto finish;
+                }
+
+                /* Always update the limit in case it was changed. For non-memory pressure detection the value is
+                 * ignored so always updating it here is not a problem. */
+                ctx = hashmap_get(monitor_hm, reply.path);
+                if (ctx)
+                        ctx->mem_pressure_limit = limit;
+        }
+
+finish:
+        if (!FLAGS_SET(flags, VARLINK_REPLY_CONTINUES))
+                m->varlink = varlink_close_unref(link);
+
+        return r;
+}
+
+/* Fill `new_h` with `path`'s descendent OomdCGroupContexts. Only include descendent cgroups that are possible
+ * candidates for action. That is, only leaf cgroups or cgroups with memory.oom.group set to "1".
+ *
+ * This function ignores most errors in order to handle cgroups that may have been cleaned up while populating
+ * the hashmap.
+ *
+ * `new_h` is of the form { key: cgroup paths -> value: OomdCGroupContext } */
+static int recursively_get_cgroup_context(Hashmap *new_h, const char *path) {
+        _cleanup_free_ char *subpath = NULL;
+        _cleanup_closedir_ DIR *d = NULL;
+        int r;
+
+        assert(new_h);
+        assert(path);
+
+        r = cg_enumerate_subgroups(SYSTEMD_CGROUP_CONTROLLER, path, &d);
+        if (r < 0)
+                return r;
+
+        r = cg_read_subgroup(d, &subpath);
+        if (r < 0)
+                return r;
+        else if (r == 0) { /* No subgroups? We're a leaf node */
+                r = oomd_insert_cgroup_context(NULL, new_h, path);
+                return (r == -ENOMEM) ? r : 0;
+        }
+
+        do {
+                _cleanup_free_ char *cg_path = NULL;
+                bool oom_group;
+
+                cg_path = path_join(empty_to_root(path), subpath);
+                if (!cg_path)
+                        return -ENOMEM;
+
+                subpath = mfree(subpath);
+
+                r = cg_get_attribute_as_bool("memory", cg_path, "memory.oom.group", &oom_group);
+                /* The cgroup might be gone. Skip it as a candidate since we can't get information on it. */
+                if (r < 0)
+                        return (r == -ENOMEM) ? r : 0;
+
+                if (oom_group) {
+                        r = oomd_insert_cgroup_context(NULL, new_h, cg_path);
+                        if (r == -ENOMEM)
+                                return r;
+                } else {
+                        r = recursively_get_cgroup_context(new_h, cg_path);
+                        if (r == -ENOMEM)
+                                return r;
+                }
+        } while ((r = cg_read_subgroup(d, &subpath)) > 0);
+
+        return 0;
+}
+
+static int update_monitored_cgroup_contexts(Hashmap **monitored_cgroups) {
+        _cleanup_hashmap_free_ Hashmap *new_base = NULL;
+        OomdCGroupContext *ctx;
+        int r;
+
+        assert(monitored_cgroups);
+
+        new_base = hashmap_new(&oomd_cgroup_ctx_hash_ops);
+        if (!new_base)
+                return -ENOMEM;
+
+        HASHMAP_FOREACH(ctx, *monitored_cgroups) {
+                /* Skip most errors since the cgroup we're trying to update might not exist anymore. */
+                r = oomd_insert_cgroup_context(*monitored_cgroups, new_base, ctx->path);
+                if (r == -ENOMEM)
+                        return r;
+        }
+
+        hashmap_free(*monitored_cgroups);
+        *monitored_cgroups = TAKE_PTR(new_base);
+
+        return 0;
+}
+
+static int get_monitored_cgroup_contexts_candidates(Hashmap *monitored_cgroups, Hashmap **ret_candidates) {
+        _cleanup_hashmap_free_ Hashmap *candidates = NULL;
+        OomdCGroupContext *ctx;
+        int r;
+
+        assert(monitored_cgroups);
+        assert(ret_candidates);
+
+        candidates = hashmap_new(&oomd_cgroup_ctx_hash_ops);
+        if (!candidates)
+                return -ENOMEM;
+
+        HASHMAP_FOREACH(ctx, monitored_cgroups) {
+                r = recursively_get_cgroup_context(candidates, ctx->path);
+                if (r == -ENOMEM)
+                        return r;
+        }
+
+        *ret_candidates = TAKE_PTR(candidates);
+
+        return 0;
+}
+
+static int acquire_managed_oom_connect(Manager *m) {
+        _cleanup_(varlink_close_unrefp) Varlink *link = NULL;
+        int r;
+
+        assert(m);
+        assert(m->event);
+
+        r = varlink_connect_address(&link, VARLINK_ADDR_PATH_MANAGED_OOM);
+        if (r < 0)
+                return log_error_errno(r, "Failed to connect to %s: %m", VARLINK_ADDR_PATH_MANAGED_OOM);
+
+        (void) varlink_set_userdata(link, m);
+        (void) varlink_set_description(link, "oomd");
+        (void) varlink_set_relative_timeout(link, USEC_INFINITY);
+
+        r = varlink_attach_event(link, m->event, SD_EVENT_PRIORITY_NORMAL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to attach varlink connection to event loop: %m");
+
+        r = varlink_bind_reply(link, process_managed_oom_reply);
+        if (r < 0)
+                return log_error_errno(r, "Failed to bind reply callback: %m");
+
+        r = varlink_observe(link, "io.systemd.ManagedOOM.SubscribeManagedOOMCGroups", NULL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to observe varlink call: %m");
+
+        m->varlink = TAKE_PTR(link);
+        return 0;
+}
+
+static int monitor_cgroup_contexts_handler(sd_event_source *s, uint64_t usec, void *userdata) {
+        _cleanup_set_free_ Set *targets = NULL;
+        Manager *m = userdata;
+        usec_t usec_now;
+        int r;
+
+        assert(s);
+        assert(userdata);
+
+        /* Reset timer */
+        r = sd_event_now(sd_event_source_get_event(s), CLOCK_MONOTONIC, &usec_now);
+        if (r < 0)
+                return log_error_errno(r, "Failed to reset event timer");
+
+        r = sd_event_source_set_time_relative(s, INTERVAL_USEC);
+        if (r < 0)
+                return log_error_errno(r, "Failed to set relative time for timer");
+
+        /* Reconnect if our connection dropped */
+        if (!m->varlink) {
+                r = acquire_managed_oom_connect(m);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to acquire varlink connection");
+        }
+
+        /* Update the cgroups used for detection/action */
+        r = update_monitored_cgroup_contexts(&m->monitored_swap_cgroup_contexts);
+        if (r == -ENOMEM)
+                return log_error_errno(r, "Failed to update monitored swap cgroup contexts");
+
+        r = update_monitored_cgroup_contexts(&m->monitored_mem_pressure_cgroup_contexts);
+        if (r == -ENOMEM)
+                return log_error_errno(r, "Failed to update monitored memory pressure cgroup contexts");
+
+        r = oomd_system_context_acquire("/proc/swaps", &m->system_context);
+        /* If there aren't units depending on swap actions, the only error we exit on is ENOMEM */
+        if (r == -ENOMEM || (r < 0 && !hashmap_isempty(m->monitored_swap_cgroup_contexts)))
+                return log_error_errno(r, "Failed to acquire system context");
+
+        /* If we're still recovering from a kill, don't try to kill again yet */
+        if (m->post_action_delay_start > 0) {
+                if (m->post_action_delay_start + POST_ACTION_DELAY_USEC > usec_now)
+                        return 0;
+                else
+                        m->post_action_delay_start = 0;
+        }
+
+        r = oomd_pressure_above(m->monitored_mem_pressure_cgroup_contexts, PRESSURE_DURATION_USEC, &targets);
+        if (r == -ENOMEM)
+                return log_error_errno(r, "Failed to check if memory pressure exceeded limits");
+        else if (r == 1) {
+                /* Check if there was reclaim activity in the last interval. The concern is the following case:
+                 * Pressure climbed, a lot of high-frequency pages were reclaimed, and we killed the offending
+                 * cgroup. Even after this, well-behaved processes will fault in recently resident pages and
+                 * this will cause pressure to remain high. Thus if there isn't any reclaim pressure, no need
+                 * to kill something (it won't help anyways). */
+                if (oomd_memory_reclaim(m->monitored_mem_pressure_cgroup_contexts)) {
+                        _cleanup_hashmap_free_ Hashmap *candidates = NULL;
+                        OomdCGroupContext *t;
+
+                        r = get_monitored_cgroup_contexts_candidates(m->monitored_mem_pressure_cgroup_contexts, &candidates);
+                        if (r == -ENOMEM)
+                                return log_error_errno(r, "Failed to get monitored memory pressure cgroup candidates");
+
+                        SET_FOREACH(t, targets) {
+                                log_notice("Memory pressure for %s is greater than %lu for more than %"PRIu64" seconds and there was reclaim activity",
+                                        t->path, LOAD_INT(t->mem_pressure_limit), PRESSURE_DURATION_USEC / USEC_PER_SEC);
+
+                                r = oomd_kill_by_pgscan(candidates, t->path, m->dry_run);
+                                if (r == -ENOMEM)
+                                        return log_error_errno(r, "Failed to kill cgroup processes by pgscan");
+                                if (r < 0)
+                                        log_info("Failed to kill any cgroup(s) under %s based on pressure", t->path);
+                                else {
+                                        /* Don't act on all the high pressure cgroups at once; return as soon as we kill one */
+                                        m->post_action_delay_start = usec_now;
+                                        return 0;
+                                }
+                        }
+                }
+        }
+
+        if (oomd_swap_free_below(&m->system_context, (100 - m->swap_used_limit))) {
+                _cleanup_hashmap_free_ Hashmap *candidates = NULL;
+
+                log_notice("Swap used (%"PRIu64") / total (%"PRIu64") is more than %u%%",
+                        m->system_context.swap_used, m->system_context.swap_total, m->swap_used_limit);
+
+                r = get_monitored_cgroup_contexts_candidates(m->monitored_swap_cgroup_contexts, &candidates);
+                if (r == -ENOMEM)
+                        return log_error_errno(r, "Failed to get monitored swap cgroup candidates");
+
+                r = oomd_kill_by_swap_usage(candidates, m->dry_run);
+                if (r == -ENOMEM)
+                        return log_error_errno(r, "Failed to kill cgroup processes by swap usage");
+                if (r < 0)
+                        log_info("Failed to kill any cgroup(s) based on swap");
+                else {
+                        m->post_action_delay_start = usec_now;
+                        return 0;
+                }
+        }
+
+        return 0;
+}
+
+static int monitor_cgroup_contexts(Manager *m) {
+        _cleanup_(sd_event_source_unrefp) sd_event_source *s = NULL;
+        int r;
+
+        assert(m);
+        assert(m->event);
+
+        r = sd_event_add_time(m->event, &s, CLOCK_MONOTONIC, 0, 0, monitor_cgroup_contexts_handler, m);
+        if (r < 0)
+                return r;
+
+        r = sd_event_source_set_exit_on_failure(s, true);
+        if (r < 0)
+                return r;
+
+        r = sd_event_source_set_enabled(s, SD_EVENT_ON);
+        if (r < 0)
+                return r;
+
+        (void) sd_event_source_set_description(s, "oomd-timer");
+
+        m->cgroup_context_event_source = TAKE_PTR(s);
+        return 0;
+}
+
+void manager_free(Manager *m) {
+        assert(m);
+
+        varlink_close_unref(m->varlink);
+        sd_event_source_unref(m->cgroup_context_event_source);
+        sd_event_unref(m->event);
+
+        hashmap_free(m->monitored_swap_cgroup_contexts);
+        hashmap_free(m->monitored_mem_pressure_cgroup_contexts);
+
+        free(m);
+}
+
+int manager_new(Manager **ret) {
+        _cleanup_(manager_freep) Manager *m = NULL;
+        int r;
+
+        assert(ret);
+
+        m = new0(Manager, 1);
+        if (!m)
+                return -ENOMEM;
+
+        r = sd_event_default(&m->event);
+        if (r < 0)
+                return r;
+
+        (void) sd_event_set_watchdog(m->event, true);
+
+        r = sd_event_add_signal(m->event, NULL, SIGINT, NULL, NULL);
+        if (r < 0)
+                return r;
+
+        r = sd_event_add_signal(m->event, NULL, SIGTERM, NULL, NULL);
+        if (r < 0)
+                return r;
+
+        m->monitored_swap_cgroup_contexts = hashmap_new(&oomd_cgroup_ctx_hash_ops);
+        if (!m->monitored_swap_cgroup_contexts)
+                return -ENOMEM;
+
+        m->monitored_mem_pressure_cgroup_contexts = hashmap_new(&oomd_cgroup_ctx_hash_ops);
+        if (!m->monitored_mem_pressure_cgroup_contexts)
+                return -ENOMEM;
+
+        *ret = TAKE_PTR(m);
+        return 0;
+}
+
+int manager_start(Manager *m, bool dry_run, int swap_used_limit, int mem_pressure_limit) {
+        unsigned long l;
+        int r;
+
+        assert(m);
+
+        m->dry_run = dry_run;
+
+        m->swap_used_limit = swap_used_limit != -1 ? swap_used_limit : DEFAULT_SWAP_USED_LIMIT;
+        assert(m->swap_used_limit <= 100);
+
+        l = mem_pressure_limit != -1 ? mem_pressure_limit : DEFAULT_MEM_PRESSURE_LIMIT;
+        r = store_loadavg_fixed_point(l, 0, &m->default_mem_pressure_limit);
+        if (r < 0)
+                return r;
+
+        r = acquire_managed_oom_connect(m);
+        if (r < 0)
+                return r;
+
+        r = monitor_cgroup_contexts(m);
+        if (r < 0)
+                return r;
+
+        return 0;
+}

src/oom/oomd-manager.h

@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+#include "conf-parser.h"
+#include "oomd-util.h"
+#include "sd-event.h"
+#include "varlink.h"
+
+/* Polling interval for monitoring stats */
+#define INTERVAL_USEC (1 * USEC_PER_SEC)
+
+/* Used to weight the averages */
+#define AVERAGE_SIZE_DECAY 4
+
+/* Take action if 10s of memory pressure > 60 for more than 30s. We use the "full" value from PSI so this is the
+ * percentage of time all tasks were delayed (i.e. unproductive).
+ * Generally 60 or higher might be acceptable for something like system.slice with no memory.high set; processes in
+ * system.slice are assumed to be less latency sensitive. */
+#define PRESSURE_DURATION_USEC (30 * USEC_PER_SEC)
+#define DEFAULT_MEM_PRESSURE_LIMIT 60
+#define DEFAULT_SWAP_USED_LIMIT 90
+
+#define POST_ACTION_DELAY_USEC (15 * USEC_PER_SEC)
+
+typedef struct Manager Manager;
+
+struct Manager {
+        sd_event *event;
+
+        bool dry_run;
+        unsigned swap_used_limit;
+        loadavg_t default_mem_pressure_limit;
+
+        /* k: cgroup paths -> v: OomdCGroupContext
+         * Used to detect when to take action. */
+        Hashmap *monitored_swap_cgroup_contexts;
+        Hashmap *monitored_mem_pressure_cgroup_contexts;
+
+        OomdSystemContext system_context;
+
+        usec_t post_action_delay_start;
+
+        sd_event_source *cgroup_context_event_source;
+
+        Varlink *varlink;
+};
+
+void manager_free(Manager *m);
+DEFINE_TRIVIAL_CLEANUP_FUNC(Manager*, manager_free);
+
+int manager_new(Manager **ret);
+
+int manager_start(Manager *m, bool dry_run, int swap_used_limit, int mem_pressure_limit);

src/oom/oomd-util.c

@@ -3,6 +3,7 @@
 #include <sys/xattr.h>
 #include <unistd.h>
 
+#include "cgroup-util.h"
 #include "fd-util.h"
 #include "format-util.h"
 #include "oomd-util.h"

src/oom/oomd.c

@@ -0,0 +1,144 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <getopt.h>
+
+#include "cgroup-util.h"
+#include "conf-parser.h"
+#include "daemon-util.h"
+#include "log.h"
+#include "main-func.h"
+#include "oomd-manager.h"
+#include "parse-util.h"
+#include "pretty-print.c"
+#include "psi-util.h"
+#include "signal-util.h"
+
+static bool arg_dry_run = false;
+static int arg_swap_used_limit = -1;
+static int arg_mem_pressure_limit = -1;
+
+static int parse_config(void) {
+        static const ConfigTableItem items[] = {
+                { "OOM", "SwapUsedLimitPercent",              config_parse_percent, 0, &arg_swap_used_limit    },
+                { "OOM", "DefaultMemoryPressureLimitPercent", config_parse_percent, 0, &arg_mem_pressure_limit },
+                {}
+        };
+
+        return config_parse_many_nulstr(PKGSYSCONFDIR "/oomd.conf",
+                                        CONF_PATHS_NULSTR("systemd/oomd.conf.d"),
+                                        "OOM\0",
+                                        config_item_table_lookup,
+                                        items,
+                                        CONFIG_PARSE_WARN,
+                                        NULL,
+                                        NULL);
+}
+
+static int help(void) {
+        _cleanup_free_ char *link = NULL;
+        int r;
+
+        r = terminal_urlify_man("systemd-oomd", "1", &link);
+        if (r < 0)
+                return log_oom();
+
+        printf("%s [OPTIONS...]\n\n"
+                        "Run the userspace out-of-memory (OOM) killer.\n\n"
+                        "  -h --help     Show this help\n"
+                        "     --dry-run  Log write/destructive actions instead of doing them\n"
+                        "\nSee the %s for details.\n"
+                        , program_invocation_short_name
+                        , link
+              );
+
+        return 0;
+}
+
+static int parse_argv(int argc, char *argv[]) {
+        enum {
+                ARG_DRY_RUN,
+        };
+
+        static const struct option options[] = {
+                { "help",    no_argument, NULL, 'h'         },
+                { "dry-run", no_argument, NULL, ARG_DRY_RUN },
+                {}
+        };
+
+        int c;
+
+        assert(argc >= 0);
+        assert(argv);
+
+        while ((c = getopt_long(argc, argv, "h", options, NULL)) >= 0)
+
+                switch (c) {
+
+                        case 'h':
+                                return help();
+
+                        case ARG_DRY_RUN:
+                                arg_dry_run = true;
+                                break;
+
+                        case '?':
+                                return -EINVAL;
+
+                        default:
+                                assert_not_reached("Invalid option passed.");
+                }
+
+        return 1;
+}
+
+static int run(int argc, char *argv[]) {
+        _cleanup_(notify_on_cleanup) const char *notify_msg = NULL;
+        _cleanup_(manager_freep) Manager *m = NULL;
+        int r;
+
+        log_setup_service();
+
+        r = parse_argv(argc, argv);
+        if (r <= 0)
+                return r;
+
+        r = parse_config();
+        if (r < 0)
+                return r;
+
+        /* Do some basic requirement checks for running systemd-oomd. It's not exhaustive as some of the other
+         * requirements do not have a reliable means to check for in code. */
+        if (access("/proc/swaps", F_OK) < 0)
+                return log_error_errno(errno, "Swap not enabled: %m");
+
+        if (!is_pressure_supported())
+                return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Pressure Stall Information (PSI) is not supported");
+
+        r = cg_all_unified();
+        if (r < 0)
+                return log_error_errno(r, "Failed to determine whether the unified cgroups hierarchy is used: %m");
+        if (r == 0)
+                return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Requires the unified cgroups hierarchy");
+
+        assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, -1) >= 0);
+
+        r = manager_new(&m);
+        if (r < 0)
+                return log_error_errno(r, "Failed to create manager: %m");
+
+        r = manager_start(m, arg_dry_run, arg_swap_used_limit, arg_mem_pressure_limit);
+        if (r < 0)
+                return log_error_errno(r, "Failed to start up daemon: %m");
+
+        notify_msg = notify_start(NOTIFY_READY, NOTIFY_STOPPING);
+
+        log_info("systemd-oomd starting%s!", arg_dry_run ? " in dry run mode" : "");
+
+        r = sd_event_loop(m->event);
+        if (r < 0)
+                return log_error_errno(r, "Event loop failed: %m");
+
+        return 0;
+}
+
+DEFINE_MAIN_FUNCTION(run);

src/oom/oomd.conf

@@ -0,0 +1,16 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+#
+# Entries in this file show the compile time defaults.
+# You can change settings by editing this file.
+# Defaults can be restored by simply deleting this file.
+#
+# See oomd.conf(5) for details
+
+[OOM]
+#SwapUsedLimitPercent=90%
+#DefaultMemoryPressureLimitPercent=60%

src/shared/conf-parser.c

@@ -1243,3 +1243,5 @@ int config_parse_vlanprotocol(const char* unit,
 
         return 0;
 }
+
+DEFINE_CONFIG_PARSE(config_parse_percent, parse_percent, "Failed to parse percent value");

src/shared/conf-parser.h

@@ -147,6 +147,7 @@ CONFIG_PARSER_PROTOTYPE(config_parse_ip_port);
 CONFIG_PARSER_PROTOTYPE(config_parse_mtu);
 CONFIG_PARSER_PROTOTYPE(config_parse_rlimit);
 CONFIG_PARSER_PROTOTYPE(config_parse_vlanprotocol);
+CONFIG_PARSER_PROTOTYPE(config_parse_percent);
 
 typedef enum Disabled {
         DISABLED_CONFIGURATION,