Merge pull request #1116 from poettering/unified-rebased

core: unified cgroup hierarchy support

13 files changed, 678 insertions, 304 deletions

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index e92d2cc850..a70b4d33ae 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -283,7 +283,7 @@ fail:
         return -errno;
 }
 
-void cgroup_context_apply(CGroupContext *c, CGroupControllerMask mask, const char *path, ManagerState state) {
+void cgroup_context_apply(CGroupContext *c, CGroupMask mask, const char *path, ManagerState state) {
         bool is_root;
         int r;
 
@@ -304,7 +304,7 @@ void cgroup_context_apply(CGroupContext *c, CGroupControllerMask mask, const cha
          * cgroup trees (assuming we are running in a container then),
          * and missing cgroups, i.e. EROFS and ENOENT. */
 
-        if ((mask & CGROUP_CPU) && !is_root) {
+        if ((mask & CGROUP_MASK_CPU) && !is_root) {
                 char buf[MAX(DECIMAL_STR_MAX(unsigned long), DECIMAL_STR_MAX(usec_t)) + 1];
 
                 sprintf(buf, "%lu\n",
@@ -331,7 +331,7 @@ void cgroup_context_apply(CGroupContext *c, CGroupControllerMask mask, const cha
                                        "Failed to set cpu.cfs_quota_us on %s: %m", path);
         }
 
-        if (mask & CGROUP_BLKIO) {
+        if (mask & CGROUP_MASK_BLKIO) {
                 char buf[MAX3(DECIMAL_STR_MAX(unsigned long)+1,
                               DECIMAL_STR_MAX(dev_t)*2+2+DECIMAL_STR_MAX(unsigned long)*1,
                               DECIMAL_STR_MAX(dev_t)*2+2+DECIMAL_STR_MAX(uint64_t)+1)];
@@ -381,21 +381,30 @@ void cgroup_context_apply(CGroupContext *c, CGroupControllerMask mask, const cha
                 }
         }
 
-        if ((mask & CGROUP_MEMORY) && !is_root) {
+        if ((mask & CGROUP_MASK_MEMORY) && !is_root) {
                 if (c->memory_limit != (uint64_t) -1) {
                         char buf[DECIMAL_STR_MAX(uint64_t) + 1];
 
                         sprintf(buf, "%" PRIu64 "\n", c->memory_limit);
-                        r = cg_set_attribute("memory", path, "memory.limit_in_bytes", buf);
-                } else
-                        r = cg_set_attribute("memory", path, "memory.limit_in_bytes", "-1");
+
+                        if (cg_unified() <= 0)
+                                r = cg_set_attribute("memory", path, "memory.limit_in_bytes", buf);
+                        else
+                                r = cg_set_attribute("memory", path, "memory.max", buf);
+
+                } else {
+                        if (cg_unified() <= 0)
+                                r = cg_set_attribute("memory", path, "memory.limit_in_bytes", "-1");
+                        else
+                                r = cg_set_attribute("memory", path, "memory.max", "max");
+                }
 
                 if (r < 0)
                         log_full_errno(IN_SET(r, -ENOENT, -EROFS) ? LOG_DEBUG : LOG_WARNING, r,
-                                       "Failed to set memory.limit_in_bytes on %s: %m", path);
+                                       "Failed to set memory.limit_in_bytes/memory.max on %s: %m", path);
         }
 
-        if ((mask & CGROUP_DEVICE) && !is_root) {
+        if ((mask & CGROUP_MASK_DEVICE) && !is_root) {
                 CGroupDeviceAllow *a;
 
                 /* Changing the devices list of a populated cgroup
@@ -459,8 +468,8 @@ void cgroup_context_apply(CGroupContext *c, CGroupControllerMask mask, const cha
         }
 }
 
-CGroupControllerMask cgroup_context_get_mask(CGroupContext *c) {
-        CGroupControllerMask mask = 0;
+CGroupMask cgroup_context_get_mask(CGroupContext *c) {
+        CGroupMask mask = 0;
 
         /* Figure out which controllers we need */
 
@@ -468,29 +477,31 @@ CGroupControllerMask cgroup_context_get_mask(CGroupContext *c) {
             c->cpu_shares != (unsigned long) -1 ||
             c->startup_cpu_shares != (unsigned long) -1 ||
             c->cpu_quota_per_sec_usec != USEC_INFINITY)
-                mask |= CGROUP_CPUACCT | CGROUP_CPU;
+                mask |= CGROUP_MASK_CPUACCT | CGROUP_MASK_CPU;
 
         if (c->blockio_accounting ||
             c->blockio_weight != (unsigned long) -1 ||
             c->startup_blockio_weight != (unsigned long) -1 ||
             c->blockio_device_weights ||
             c->blockio_device_bandwidths)
-                mask |= CGROUP_BLKIO;
+                mask |= CGROUP_MASK_BLKIO;
 
         if (c->memory_accounting ||
             c->memory_limit != (uint64_t) -1)
-                mask |= CGROUP_MEMORY;
+                mask |= CGROUP_MASK_MEMORY;
 
         if (c->device_allow ||
             c->device_policy != CGROUP_AUTO)
-                mask |= CGROUP_DEVICE;
+                mask |= CGROUP_MASK_DEVICE;
 
         return mask;
 }
 
-CGroupControllerMask unit_get_cgroup_mask(Unit *u) {
+CGroupMask unit_get_own_mask(Unit *u) {
         CGroupContext *c;
 
+        /* Returns the mask of controllers the unit needs for itself */
+
         c = unit_get_cgroup_context(u);
         if (!c)
                 return 0;
@@ -505,15 +516,18 @@ CGroupControllerMask unit_get_cgroup_mask(Unit *u) {
 
                 e = unit_get_exec_context(u);
                 if (!e || exec_context_maintains_privileges(e))
-                        return _CGROUP_CONTROLLER_MASK_ALL;
+                        return _CGROUP_MASK_ALL;
         }
 
         return cgroup_context_get_mask(c);
 }
 
-CGroupControllerMask unit_get_members_mask(Unit *u) {
+CGroupMask unit_get_members_mask(Unit *u) {
         assert(u);
 
+        /* Returns the mask of controllers all of the unit's children
+         * require, merged */
+
         if (u->cgroup_members_mask_valid)
                 return u->cgroup_members_mask;
 
@@ -532,7 +546,7 @@ CGroupControllerMask unit_get_members_mask(Unit *u) {
                                 continue;
 
                         u->cgroup_members_mask |=
-                                unit_get_cgroup_mask(member) |
+                                unit_get_own_mask(member) |
                                 unit_get_members_mask(member);
                 }
         }
@@ -541,19 +555,52 @@ CGroupControllerMask unit_get_members_mask(Unit *u) {
         return u->cgroup_members_mask;
 }
 
-CGroupControllerMask unit_get_siblings_mask(Unit *u) {
+CGroupMask unit_get_siblings_mask(Unit *u) {
         assert(u);
 
+        /* Returns the mask of controllers all of the unit's siblings
+         * require, i.e. the members mask of the unit's parent slice
+         * if there is one. */
+
         if (UNIT_ISSET(u->slice))
                 return unit_get_members_mask(UNIT_DEREF(u->slice));
 
-        return unit_get_cgroup_mask(u) | unit_get_members_mask(u);
+        return unit_get_own_mask(u) | unit_get_members_mask(u);
 }
 
-CGroupControllerMask unit_get_target_mask(Unit *u) {
-        CGroupControllerMask mask;
+CGroupMask unit_get_subtree_mask(Unit *u) {
+
+        /* Returns the mask of this subtree, meaning of the group
+         * itself and its children. */
+
+        return unit_get_own_mask(u) | unit_get_members_mask(u);
+}
+
+CGroupMask unit_get_target_mask(Unit *u) {
+        CGroupMask mask;
+
+        /* This returns the cgroup mask of all controllers to enable
+         * for a specific cgroup, i.e. everything it needs itself,
+         * plus all that its children need, plus all that its siblings
+         * need. This is primarily useful on the legacy cgroup
+         * hierarchy, where we need to duplicate each cgroup in each
+         * hierarchy that shall be enabled for it. */
 
-        mask = unit_get_cgroup_mask(u) | unit_get_members_mask(u) | unit_get_siblings_mask(u);
+        mask = unit_get_own_mask(u) | unit_get_members_mask(u) | unit_get_siblings_mask(u);
+        mask &= u->manager->cgroup_supported;
+
+        return mask;
+}
+
+CGroupMask unit_get_enable_mask(Unit *u) {
+        CGroupMask mask;
+
+        /* This returns the cgroup mask of all controllers to enable
+         * for the children of a specific cgroup. This is primarily
+         * useful for the unified cgroup hierarchy, where each cgroup
+         * controls which controllers are enabled for its children. */
+
+        mask = unit_get_members_mask(u);
         mask &= u->manager->cgroup_supported;
 
         return mask;
@@ -562,13 +609,13 @@ CGroupControllerMask unit_get_target_mask(Unit *u) {
 /* Recurse from a unit up through its containing slices, propagating
  * mask bits upward. A unit is also member of itself. */
 void unit_update_cgroup_members_masks(Unit *u) {
-        CGroupControllerMask m;
+        CGroupMask m;
         bool more;
 
         assert(u);
 
         /* Calculate subtree mask */
-        m = unit_get_cgroup_mask(u) | unit_get_members_mask(u);
+        m = unit_get_subtree_mask(u);
 
         /* See if anything changed from the previous invocation. If
          * not, we're done. */
@@ -608,7 +655,7 @@ void unit_update_cgroup_members_masks(Unit *u) {
         }
 }
 
-static const char *migrate_callback(CGroupControllerMask mask, void *userdata) {
+static const char *migrate_callback(CGroupMask mask, void *userdata) {
         Unit *u = userdata;
 
         assert(mask != 0);
@@ -626,7 +673,115 @@ static const char *migrate_callback(CGroupControllerMask mask, void *userdata) {
         return NULL;
 }
 
-static int unit_create_cgroups(Unit *u, CGroupControllerMask mask) {
+char *unit_default_cgroup_path(Unit *u) {
+        _cleanup_free_ char *escaped = NULL, *slice = NULL;
+        int r;
+
+        assert(u);
+
+        if (unit_has_name(u, SPECIAL_ROOT_SLICE))
+                return strdup(u->manager->cgroup_root);
+
+        if (UNIT_ISSET(u->slice) && !unit_has_name(UNIT_DEREF(u->slice), SPECIAL_ROOT_SLICE)) {
+                r = cg_slice_to_path(UNIT_DEREF(u->slice)->id, &slice);
+                if (r < 0)
+                        return NULL;
+        }
+
+        escaped = cg_escape(u->id);
+        if (!escaped)
+                return NULL;
+
+        if (slice)
+                return strjoin(u->manager->cgroup_root, "/", slice, "/", escaped, NULL);
+        else
+                return strjoin(u->manager->cgroup_root, "/", escaped, NULL);
+}
+
+int unit_set_cgroup_path(Unit *u, const char *path) {
+        _cleanup_free_ char *p = NULL;
+        int r;
+
+        assert(u);
+
+        if (path) {
+                p = strdup(path);
+                if (!p)
+                        return -ENOMEM;
+        } else
+                p = NULL;
+
+        if (streq_ptr(u->cgroup_path, p))
+                return 0;
+
+        if (p) {
+                r = hashmap_put(u->manager->cgroup_unit, p, u);
+                if (r < 0)
+                        return r;
+        }
+
+        unit_release_cgroup(u);
+
+        u->cgroup_path = p;
+        p = NULL;
+
+        return 1;
+}
+
+int unit_watch_cgroup(Unit *u) {
+        _cleanup_free_ char *populated = NULL;
+        int r;
+
+        assert(u);
+
+        if (!u->cgroup_path)
+                return 0;
+
+        if (u->cgroup_inotify_wd >= 0)
+                return 0;
+
+        /* Only applies to the unified hierarchy */
+        r = cg_unified();
+        if (r < 0)
+                return log_unit_error_errno(u, r, "Failed detect wether the unified hierarchy is used: %m");
+        if (r == 0)
+                return 0;
+
+        /* Don't watch the root slice, it's pointless. */
+        if (unit_has_name(u, SPECIAL_ROOT_SLICE))
+                return 0;
+
+        r = hashmap_ensure_allocated(&u->manager->cgroup_inotify_wd_unit, &trivial_hash_ops);
+        if (r < 0)
+                return log_oom();
+
+        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, "cgroup.populated", &populated);
+        if (r < 0)
+                return log_oom();
+
+        u->cgroup_inotify_wd = inotify_add_watch(u->manager->cgroup_inotify_fd, populated, IN_MODIFY);
+        if (u->cgroup_inotify_wd < 0) {
+
+                if (errno == ENOENT) /* If the directory is already
+                                      * gone we don't need to track
+                                      * it, so this is not an error */
+                        return 0;
+
+                return log_unit_error_errno(u, errno, "Failed to add inotify watch descriptor for control group %s: %m", u->cgroup_path);
+        }
+
+        r = hashmap_put(u->manager->cgroup_inotify_wd_unit, INT_TO_PTR(u->cgroup_inotify_wd), u);
+        if (r < 0)
+                return log_unit_error_errno(u, r, "Failed to add inotify watch descriptor to hash map: %m");
+
+        return 0;
+}
+
+static int unit_create_cgroup(
+                Unit *u,
+                CGroupMask target_mask,
+                CGroupMask enable_mask) {
+
         CGroupContext *c;
         int r;
 
@@ -643,25 +798,29 @@ static int unit_create_cgroups(Unit *u, CGroupControllerMask mask) {
                 if (!path)
                         return log_oom();
 
-                r = hashmap_put(u->manager->cgroup_unit, path, u);
-                if (r < 0) {
-                        log_error(r == -EEXIST ? "cgroup %s exists already: %s" : "hashmap_put failed for %s: %s", path, strerror(-r));
-                        return r;
-                }
-                if (r > 0) {
-                        u->cgroup_path = path;
-                        path = NULL;
-                }
+                r = unit_set_cgroup_path(u, path);
+                if (r == -EEXIST)
+                        return log_unit_error_errno(u, r, "Control group %s exists already.", path);
+                if (r < 0)
+                        return log_unit_error_errno(u, r, "Failed to set unit's control group path to %s: %m", path);
         }
 
         /* First, create our own group */
-        r = cg_create_everywhere(u->manager->cgroup_supported, mask, u->cgroup_path);
+        r = cg_create_everywhere(u->manager->cgroup_supported, target_mask, u->cgroup_path);
+        if (r < 0)
+                return log_unit_error_errno(u, r, "Failed to create cgroup %s: %m", u->cgroup_path);
+
+        /* Start watching it */
+        (void) unit_watch_cgroup(u);
+
+        /* Enable all controllers we need */
+        r = cg_enable_everywhere(u->manager->cgroup_supported, enable_mask, u->cgroup_path);
         if (r < 0)
-                return log_error_errno(r, "Failed to create cgroup %s: %m", u->cgroup_path);
+                log_unit_warning_errno(u, r, "Failed to enable controllers on cgroup %s, ignoring: %m", u->cgroup_path);
 
         /* Keep track that this is now realized */
         u->cgroup_realized = true;
-        u->cgroup_realized_mask = mask;
+        u->cgroup_realized_mask = target_mask;
 
         if (u->type != UNIT_SLICE && !c->delegate) {
 
@@ -670,7 +829,7 @@ static int unit_create_cgroups(Unit *u, CGroupControllerMask mask) {
                  * for slice and delegation units. */
                 r = cg_migrate_everywhere(u->manager->cgroup_supported, u->cgroup_path, u->cgroup_path, migrate_callback, u);
                 if (r < 0)
-                        log_warning_errno(r, "Failed to migrate cgroup from to %s: %m", u->cgroup_path);
+                        log_unit_warning_errno(u, r, "Failed to migrate cgroup from to %s, ignoring: %m", u->cgroup_path);
         }
 
         return 0;
@@ -691,10 +850,10 @@ int unit_attach_pids_to_cgroup(Unit *u) {
         return 0;
 }
 
-static bool unit_has_mask_realized(Unit *u, CGroupControllerMask mask) {
+static bool unit_has_mask_realized(Unit *u, CGroupMask target_mask) {
         assert(u);
 
-        return u->cgroup_realized && u->cgroup_realized_mask == mask;
+        return u->cgroup_realized && u->cgroup_realized_mask == target_mask;
 }
 
 /* Check if necessary controllers and attributes for a unit are in place.
@@ -704,7 +863,7 @@ static bool unit_has_mask_realized(Unit *u, CGroupControllerMask mask) {
  *
  * Returns 0 on success and < 0 on failure. */
 static int unit_realize_cgroup_now(Unit *u, ManagerState state) {
-        CGroupControllerMask mask;
+        CGroupMask target_mask, enable_mask;
         int r;
 
         assert(u);
@@ -714,9 +873,8 @@ static int unit_realize_cgroup_now(Unit *u, ManagerState state) {
                 u->in_cgroup_queue = false;
         }
 
-        mask = unit_get_target_mask(u);
-
-        if (unit_has_mask_realized(u, mask))
+        target_mask = unit_get_target_mask(u);
+        if (unit_has_mask_realized(u, target_mask))
                 return 0;
 
         /* First, realize parents */
@@ -727,12 +885,13 @@ static int unit_realize_cgroup_now(Unit *u, ManagerState state) {
         }
 
         /* And then do the real work */
-        r = unit_create_cgroups(u, mask);
+        enable_mask = unit_get_enable_mask(u);
+        r = unit_create_cgroup(u, target_mask, enable_mask);
         if (r < 0)
                 return r;
 
         /* Finally, apply the necessary attributes. */
-        cgroup_context_apply(unit_get_cgroup_context(u), mask, u->cgroup_path, state);
+        cgroup_context_apply(unit_get_cgroup_context(u), target_mask, u->cgroup_path, state);
 
         return 0;
 }
@@ -759,7 +918,7 @@ unsigned manager_dispatch_cgroup_queue(Manager *m) {
 
                 r = unit_realize_cgroup_now(i, state);
                 if (r < 0)
-                        log_warning_errno(r, "Failed to realize cgroups for queued unit %s: %m", i->id);
+                        log_warning_errno(r, "Failed to realize cgroups for queued unit %s, ignoring: %m", i->id);
 
                 n++;
         }
@@ -829,39 +988,67 @@ int unit_realize_cgroup(Unit *u) {
         return unit_realize_cgroup_now(u, manager_state(u->manager));
 }
 
-void unit_destroy_cgroup_if_empty(Unit *u) {
+void unit_release_cgroup(Unit *u) {
+        assert(u);
+
+        /* Forgets all cgroup details for this cgroup */
+
+        if (u->cgroup_path) {
+                (void) hashmap_remove(u->manager->cgroup_unit, u->cgroup_path);
+                u->cgroup_path = mfree(u->cgroup_path);
+        }
+
+        if (u->cgroup_inotify_wd >= 0) {
+                if (inotify_rm_watch(u->manager->cgroup_inotify_fd, u->cgroup_inotify_wd) < 0)
+                        log_unit_debug_errno(u, errno, "Failed to remove cgroup inotify watch %i for %s, ignoring", u->cgroup_inotify_wd, u->id);
+
+                (void) hashmap_remove(u->manager->cgroup_inotify_wd_unit, INT_TO_PTR(u->cgroup_inotify_wd));
+                u->cgroup_inotify_wd = -1;
+        }
+}
+
+void unit_prune_cgroup(Unit *u) {
         int r;
+        bool is_root_slice;
 
         assert(u);
 
+        /* Removes the cgroup, if empty and possible, and stops watching it. */
+
         if (!u->cgroup_path)
                 return;
 
-        r = cg_trim_everywhere(u->manager->cgroup_supported, u->cgroup_path, !unit_has_name(u, SPECIAL_ROOT_SLICE));
+        is_root_slice = unit_has_name(u, SPECIAL_ROOT_SLICE);
+
+        r = cg_trim_everywhere(u->manager->cgroup_supported, u->cgroup_path, !is_root_slice);
         if (r < 0) {
-                log_debug_errno(r, "Failed to destroy cgroup %s: %m", u->cgroup_path);
+                log_debug_errno(r, "Failed to destroy cgroup %s, ignoring: %m", u->cgroup_path);
                 return;
         }
 
-        hashmap_remove(u->manager->cgroup_unit, u->cgroup_path);
+        if (is_root_slice)
+                return;
+
+        unit_release_cgroup(u);
 
-        free(u->cgroup_path);
-        u->cgroup_path = NULL;
         u->cgroup_realized = false;
         u->cgroup_realized_mask = 0;
 }
 
-pid_t unit_search_main_pid(Unit *u) {
+int unit_search_main_pid(Unit *u, pid_t *ret) {
         _cleanup_fclose_ FILE *f = NULL;
         pid_t pid = 0, npid, mypid;
+        int r;
 
         assert(u);
+        assert(ret);
 
         if (!u->cgroup_path)
-                return 0;
+                return -ENXIO;
 
-        if (cg_enumerate_processes(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, &f) < 0)
-                return 0;
+        r = cg_enumerate_processes(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, &f);
+        if (r < 0)
+                return r;
 
         mypid = getpid();
         while (cg_read_pid(f, &npid) > 0)  {
@@ -874,90 +1061,274 @@ pid_t unit_search_main_pid(Unit *u) {
                 if (get_parent_of_pid(npid, &ppid) >= 0 && ppid != mypid)
                         continue;
 
-                if (pid != 0) {
+                if (pid != 0)
                         /* Dang, there's more than one daemonized PID
                         in this group, so we don't know what process
                         is the main process. */
-                        pid = 0;
-                        break;
-                }
+
+                        return -ENODATA;
 
                 pid = npid;
         }
 
-        return pid;
+        *ret = pid;
+        return 0;
+}
+
+static int unit_watch_pids_in_path(Unit *u, const char *path) {
+       _cleanup_closedir_ DIR *d = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
+        int ret = 0, r;
+
+        assert(u);
+        assert(path);
+
+        r = cg_enumerate_processes(SYSTEMD_CGROUP_CONTROLLER, path, &f);
+        if (r < 0)
+                ret = r;
+        else {
+                pid_t pid;
+
+                while ((r = cg_read_pid(f, &pid)) > 0) {
+                        r = unit_watch_pid(u, pid);
+                        if (r < 0 && ret >= 0)
+                                ret = r;
+                }
+
+                if (r < 0 && ret >= 0)
+                        ret = r;
+        }
+
+        r = cg_enumerate_subgroups(SYSTEMD_CGROUP_CONTROLLER, path, &d);
+        if (r < 0) {
+                if (ret >= 0)
+                        ret = r;
+        } else {
+                char *fn;
+
+                while ((r = cg_read_subgroup(d, &fn)) > 0) {
+                        _cleanup_free_ char *p = NULL;
+
+                        p = strjoin(path, "/", fn, NULL);
+                        free(fn);
+
+                        if (!p)
+                                return -ENOMEM;
+
+                        r = unit_watch_pids_in_path(u, p);
+                        if (r < 0 && ret >= 0)
+                                ret = r;
+                }
+
+                if (r < 0 && ret >= 0)
+                        ret = r;
+        }
+
+        return ret;
+}
+
+int unit_watch_all_pids(Unit *u) {
+        assert(u);
+
+        /* Adds all PIDs from our cgroup to the set of PIDs we
+         * watch. This is a fallback logic for cases where we do not
+         * get reliable cgroup empty notifications: we try to use
+         * SIGCHLD as replacement. */
+
+        if (!u->cgroup_path)
+                return -ENOENT;
+
+        if (cg_unified() > 0) /* On unified we can use proper notifications */
+                return 0;
+
+        return unit_watch_pids_in_path(u, u->cgroup_path);
+}
+
+int unit_notify_cgroup_empty(Unit *u) {
+        int r;
+
+        assert(u);
+
+        if (!u->cgroup_path)
+                return 0;
+
+        r = cg_is_empty_recursive(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path);
+        if (r <= 0)
+                return r;
+
+        unit_add_to_gc_queue(u);
+
+        if (UNIT_VTABLE(u)->notify_cgroup_empty)
+                UNIT_VTABLE(u)->notify_cgroup_empty(u);
+
+        return 0;
+}
+
+static int on_cgroup_inotify_event(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+        Manager *m = userdata;
+
+        assert(s);
+        assert(fd >= 0);
+        assert(m);
+
+        for (;;) {
+                union inotify_event_buffer buffer;
+                struct inotify_event *e;
+                ssize_t l;
+
+                l = read(fd, &buffer, sizeof(buffer));
+                if (l < 0) {
+                        if (errno == EINTR || errno == EAGAIN)
+                                return 0;
+
+                        return log_error_errno(errno, "Failed to read control group inotify events: %m");
+                }
+
+                FOREACH_INOTIFY_EVENT(e, buffer, l) {
+                        Unit *u;
+
+                        if (e->wd < 0)
+                                /* Queue overflow has no watch descriptor */
+                                continue;
+
+                        if (e->mask & IN_IGNORED)
+                                /* The watch was just removed */
+                                continue;
+
+                        u = hashmap_get(m->cgroup_inotify_wd_unit, INT_TO_PTR(e->wd));
+                        if (!u) /* Not that inotify might deliver
+                                 * events for a watch even after it
+                                 * was removed, because it was queued
+                                 * before the removal. Let's ignore
+                                 * this here safely. */
+                                continue;
+
+                        (void) unit_notify_cgroup_empty(u);
+                }
+        }
 }
 
 int manager_setup_cgroup(Manager *m) {
         _cleanup_free_ char *path = NULL;
-        int r;
+        CGroupController c;
+        int r, unified;
+        char *e;
 
         assert(m);
 
         /* 1. Determine hierarchy */
-        free(m->cgroup_root);
-        m->cgroup_root = NULL;
-
+        m->cgroup_root = mfree(m->cgroup_root);
         r = cg_pid_get_path(SYSTEMD_CGROUP_CONTROLLER, 0, &m->cgroup_root);
         if (r < 0)
                 return log_error_errno(r, "Cannot determine cgroup we are running in: %m");
 
-        /* LEGACY: Already in /system.slice? If so, let's cut this
-         * off. This is to support live upgrades from older systemd
-         * versions where PID 1 was moved there. */
-        if (m->running_as == MANAGER_SYSTEM) {
-                char *e;
+        /* Chop off the init scope, if we are already located in it */
+        e = endswith(m->cgroup_root, "/" SPECIAL_INIT_SCOPE);
 
+        /* LEGACY: Also chop off the system slice if we are in
+         * it. This is to support live upgrades from older systemd
+         * versions where PID 1 was moved there. Also see
+         * cg_get_root_path(). */
+        if (!e && m->running_as == MANAGER_SYSTEM) {
                 e = endswith(m->cgroup_root, "/" SPECIAL_SYSTEM_SLICE);
                 if (!e)
-                        e = endswith(m->cgroup_root, "/system");
-                if (e)
-                        *e = 0;
+                        e = endswith(m->cgroup_root, "/system"); /* even more legacy */
         }
+        if (e)
+                *e = 0;
 
         /* And make sure to store away the root value without trailing
          * slash, even for the root dir, so that we can easily prepend
          * it everywhere. */
-        if (streq(m->cgroup_root, "/"))
-                m->cgroup_root[0] = 0;
+        while ((e = endswith(m->cgroup_root, "/")))
+                *e = 0;
 
         /* 2. Show data */
         r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_root, NULL, &path);
         if (r < 0)
                 return log_error_errno(r, "Cannot find cgroup mount point: %m");
 
-        log_debug("Using cgroup controller " SYSTEMD_CGROUP_CONTROLLER ". File system hierarchy is at %s.", path);
+        unified = cg_unified();
+        if (unified < 0)
+                return log_error_errno(r, "Couldn't determine if we are running in the unified hierarchy: %m");
+        if (unified > 0)
+                log_debug("Unified cgroup hierarchy is located at %s.", path);
+        else
+                log_debug("Using cgroup controller " SYSTEMD_CGROUP_CONTROLLER ". File system hierarchy is at %s.", path);
+
         if (!m->test_run) {
+                const char *scope_path;
 
                 /* 3. Install agent */
-                if (m->running_as == MANAGER_SYSTEM) {
+                if (unified) {
+
+                        /* In the unified hierarchy we can can get
+                         * cgroup empty notifications via inotify. */
+
+                        m->cgroup_inotify_event_source = sd_event_source_unref(m->cgroup_inotify_event_source);
+                        safe_close(m->cgroup_inotify_fd);
+
+                        m->cgroup_inotify_fd = inotify_init1(IN_NONBLOCK|IN_CLOEXEC);
+                        if (m->cgroup_inotify_fd < 0)
+                                return log_error_errno(errno, "Failed to create control group inotify object: %m");
+
+                        r = sd_event_add_io(m->event, &m->cgroup_inotify_event_source, m->cgroup_inotify_fd, EPOLLIN, on_cgroup_inotify_event, m);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to watch control group inotify object: %m");
+
+                        r = sd_event_source_set_priority(m->cgroup_inotify_event_source, SD_EVENT_PRIORITY_IDLE - 5);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to set priority of inotify event source: %m");
+
+                        (void) sd_event_source_set_description(m->cgroup_inotify_event_source, "cgroup-inotify");
+
+                } else if (m->running_as == MANAGER_SYSTEM) {
+
+                        /* On the legacy hierarchy we only get
+                         * notifications via cgroup agents. (Which
+                         * isn't really reliable, since it does not
+                         * generate events when control groups with
+                         * children run empty. */
+
                         r = cg_install_release_agent(SYSTEMD_CGROUP_CONTROLLER, SYSTEMD_CGROUP_AGENT_PATH);
                         if (r < 0)
                                 log_warning_errno(r, "Failed to install release agent, ignoring: %m");
                         else if (r > 0)
                                 log_debug("Installed release agent.");
-                        else
+                        else if (r == 0)
                                 log_debug("Release agent already installed.");
                 }
 
-                /* 4. Make sure we are in the root cgroup */
-                r = cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_root, 0);
+                /* 4. Make sure we are in the special "init.scope" unit in the root slice. */
+                scope_path = strjoina(m->cgroup_root, "/" SPECIAL_INIT_SCOPE);
+                r = cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, scope_path, 0);
                 if (r < 0)
-                        return log_error_errno(r, "Failed to create root cgroup hierarchy: %m");
+                        return log_error_errno(r, "Failed to create %s control group: %m", scope_path);
+
+                /* also, move all other userspace processes remaining
+                 * in the root cgroup into that scope. */
+                r = cg_migrate(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_root, SYSTEMD_CGROUP_CONTROLLER, scope_path, false);
+                if (r < 0)
+                        log_warning_errno(r, "Couldn't move remaining userspace processes, ignoring: %m");
 
                 /* 5. And pin it, so that it cannot be unmounted */
                 safe_close(m->pin_cgroupfs_fd);
-
                 m->pin_cgroupfs_fd = open(path, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOCTTY|O_NONBLOCK);
                 if (m->pin_cgroupfs_fd < 0)
                         return log_error_errno(errno, "Failed to open pin file: %m");
 
                 /* 6.  Always enable hierarchical support if it exists... */
-                cg_set_attribute("memory", "/", "memory.use_hierarchy", "1");
+                if (!unified)
+                        (void) cg_set_attribute("memory", "/", "memory.use_hierarchy", "1");
         }
 
         /* 7. Figure out which controllers are supported */
-        m->cgroup_supported = cg_mask_supported();
+        r = cg_mask_supported(&m->cgroup_supported);
+        if (r < 0)
+                return log_error_errno(r, "Failed to determine supported controllers: %m");
+
+        for (c = 0; c < _CGROUP_CONTROLLER_MAX; c++)
+                log_debug("Controller '%s' supported: %s", cgroup_controller_to_string(c), yes_no(m->cgroup_supported & c));
 
         return 0;
 }
@@ -968,12 +1339,16 @@ void manager_shutdown_cgroup(Manager *m, bool delete) {
         /* We can't really delete the group, since we are in it. But
          * let's trim it. */
         if (delete && m->cgroup_root)
-                cg_trim(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_root, false);
+                (void) cg_trim(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_root, false);
+
+        m->cgroup_inotify_wd_unit = hashmap_free(m->cgroup_inotify_wd_unit);
+
+        m->cgroup_inotify_event_source = sd_event_source_unref(m->cgroup_inotify_event_source);
+        m->cgroup_inotify_fd = safe_close(m->cgroup_inotify_fd);
 
         m->pin_cgroupfs_fd = safe_close(m->pin_cgroupfs_fd);
 
-        free(m->cgroup_root);
-        m->cgroup_root = NULL;
+        m->cgroup_root = mfree(m->cgroup_root);
 }
 
 Unit* manager_get_unit_by_cgroup(Manager *m, const char *cgroup) {
@@ -992,8 +1367,8 @@ Unit* manager_get_unit_by_cgroup(Manager *m, const char *cgroup) {
                 char *e;
 
                 e = strrchr(p, '/');
-                if (e == p || !e)
-                        return NULL;
+                if (!e || e == p)
+                        return hashmap_get(m->cgroup_unit, SPECIAL_ROOT_SLICE);
 
                 *e = 0;
 
@@ -1010,9 +1385,12 @@ Unit *manager_get_unit_by_pid(Manager *m, pid_t pid) {
 
         assert(m);
 
-        if (pid <= 1)
+        if (pid <= 0)
                 return NULL;
 
+        if (pid == 1)
+                return hashmap_get(m->units, SPECIAL_INIT_SCOPE);
+
         u = hashmap_get(m->watch_pids1, LONG_TO_PTR(pid));
         if (u)
                 return u;
@@ -1030,7 +1408,6 @@ Unit *manager_get_unit_by_pid(Manager *m, pid_t pid) {
 
 int manager_notify_cgroup_empty(Manager *m, const char *cgroup) {
         Unit *u;
-        int r;
 
         assert(m);
         assert(cgroup);
@@ -1039,15 +1416,7 @@ int manager_notify_cgroup_empty(Manager *m, const char *cgroup) {
         if (!u)
                 return 0;
 
-        r = cg_is_empty_recursive(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path);
-        if (r <= 0)
-                return r;
-
-        if (UNIT_VTABLE(u)->notify_cgroup_empty)
-                UNIT_VTABLE(u)->notify_cgroup_empty(u);
-
-        unit_add_to_gc_queue(u);
-        return 0;
+        return unit_notify_cgroup_empty(u);
 }
 
 int unit_get_memory_current(Unit *u, uint64_t *ret) {
@@ -1060,10 +1429,13 @@ int unit_get_memory_current(Unit *u, uint64_t *ret) {
         if (!u->cgroup_path)
                 return -ENODATA;
 
-        if ((u->cgroup_realized_mask & CGROUP_MEMORY) == 0)
+        if ((u->cgroup_realized_mask & CGROUP_MASK_MEMORY) == 0)
                 return -ENODATA;
 
-        r = cg_get_attribute("memory", u->cgroup_path, "memory.usage_in_bytes", &v);
+        if (cg_unified() <= 0)
+                r = cg_get_attribute("memory", u->cgroup_path, "memory.usage_in_bytes", &v);
+        else
+                r = cg_get_attribute("memory", u->cgroup_path, "memory.current", &v);
         if (r == -ENOENT)
                 return -ENODATA;
         if (r < 0)
@@ -1083,7 +1455,7 @@ static int unit_get_cpu_usage_raw(Unit *u, nsec_t *ret) {
         if (!u->cgroup_path)
                 return -ENODATA;
 
-        if ((u->cgroup_realized_mask & CGROUP_CPUACCT) == 0)
+        if ((u->cgroup_realized_mask & CGROUP_MASK_CPUACCT) == 0)
                 return -ENODATA;
 
         r = cg_get_attribute("cpuacct", u->cgroup_path, "cpuacct.usage", &v);
diff --git a/src/core/cgroup.h b/src/core/cgroup.h
index 7b38d210fb..1ce21f43f2 100644
--- a/src/core/cgroup.h
+++ b/src/core/cgroup.h
@@ -96,22 +96,32 @@ struct CGroupContext {
 void cgroup_context_init(CGroupContext *c);
 void cgroup_context_done(CGroupContext *c);
 void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix);
-void cgroup_context_apply(CGroupContext *c, CGroupControllerMask mask, const char *path, ManagerState state);
+void cgroup_context_apply(CGroupContext *c, CGroupMask mask, const char *path, ManagerState state);
 
-CGroupControllerMask cgroup_context_get_mask(CGroupContext *c);
+CGroupMask cgroup_context_get_mask(CGroupContext *c);
 
 void cgroup_context_free_device_allow(CGroupContext *c, CGroupDeviceAllow *a);
 void cgroup_context_free_blockio_device_weight(CGroupContext *c, CGroupBlockIODeviceWeight *w);
 void cgroup_context_free_blockio_device_bandwidth(CGroupContext *c, CGroupBlockIODeviceBandwidth *b);
 
-CGroupControllerMask unit_get_cgroup_mask(Unit *u);
-CGroupControllerMask unit_get_siblings_mask(Unit *u);
-CGroupControllerMask unit_get_members_mask(Unit *u);
-CGroupControllerMask unit_get_target_mask(Unit *u);
+CGroupMask unit_get_own_mask(Unit *u);
+CGroupMask unit_get_siblings_mask(Unit *u);
+CGroupMask unit_get_members_mask(Unit *u);
+CGroupMask unit_get_subtree_mask(Unit *u);
+
+CGroupMask unit_get_target_mask(Unit *u);
+CGroupMask unit_get_enable_mask(Unit *u);
 
 void unit_update_cgroup_members_masks(Unit *u);
+
+char *unit_default_cgroup_path(Unit *u);
+int unit_set_cgroup_path(Unit *u, const char *path);
+
 int unit_realize_cgroup(Unit *u);
-void unit_destroy_cgroup_if_empty(Unit *u);
+void unit_release_cgroup(Unit *u);
+void unit_prune_cgroup(Unit *u);
+int unit_watch_cgroup(Unit *u);
+
 int unit_attach_pids_to_cgroup(Unit *u);
 
 int manager_setup_cgroup(Manager *m);
@@ -122,9 +132,8 @@ unsigned manager_dispatch_cgroup_queue(Manager *m);
 Unit *manager_get_unit_by_cgroup(Manager *m, const char *cgroup);
 Unit* manager_get_unit_by_pid(Manager *m, pid_t pid);
 
-pid_t unit_search_main_pid(Unit *u);
-
-int manager_notify_cgroup_empty(Manager *m, const char *group);
+int unit_search_main_pid(Unit *u, pid_t *ret);
+int unit_watch_all_pids(Unit *u);
 
 int unit_get_memory_current(Unit *u, uint64_t *ret);
 int unit_get_cpu_usage(Unit *u, nsec_t *ret);
@@ -132,5 +141,8 @@ int unit_reset_cpu_usage(Unit *u);
 
 bool unit_cgroup_delegate(Unit *u);
 
+int unit_notify_cgroup_empty(Unit *u);
+int manager_notify_cgroup_empty(Manager *m, const char *group);
+
 const char* cgroup_device_policy_to_string(CGroupDevicePolicy i) _const_;
 CGroupDevicePolicy cgroup_device_policy_from_string(const char *s) _pure_;
diff --git a/src/core/dbus-cgroup.c b/src/core/dbus-cgroup.c
index 9dcc51f240..e8fd44e294 100644
--- a/src/core/dbus-cgroup.c
+++ b/src/core/dbus-cgroup.c
@@ -228,7 +228,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->cpu_accounting = b;
-                        u->cgroup_realized_mask &= ~CGROUP_CPUACCT;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_CPUACCT;
                         unit_write_drop_in_private(u, mode, name, b ? "CPUAccounting=yes" : "CPUAccounting=no");
                 }
 
@@ -252,7 +252,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->cpu_shares = ul;
-                        u->cgroup_realized_mask &= ~CGROUP_CPU;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_CPU;
                         unit_write_drop_in_private_format(u, mode, name, "CPUShares=%lu", ul);
                 }
 
@@ -276,7 +276,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->startup_cpu_shares = ul;
-                        u->cgroup_realized_mask &= ~CGROUP_CPU;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_CPU;
                         unit_write_drop_in_private_format(u, mode, name, "StartupCPUShares=%lu", ul);
                 }
 
@@ -294,7 +294,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->cpu_quota_per_sec_usec = u64;
-                        u->cgroup_realized_mask &= ~CGROUP_CPU;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_CPU;
                         unit_write_drop_in_private_format(u, mode, "CPUQuota", "CPUQuota=%0.f%%", (double) (c->cpu_quota_per_sec_usec / 10000));
                 }
 
@@ -309,7 +309,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->blockio_accounting = b;
-                        u->cgroup_realized_mask &= ~CGROUP_BLKIO;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_BLKIO;
                         unit_write_drop_in_private(u, mode, name, b ? "BlockIOAccounting=yes" : "BlockIOAccounting=no");
                 }
 
@@ -333,7 +333,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->blockio_weight = ul;
-                        u->cgroup_realized_mask &= ~CGROUP_BLKIO;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_BLKIO;
                         unit_write_drop_in_private_format(u, mode, name, "BlockIOWeight=%lu", ul);
                 }
 
@@ -357,7 +357,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->startup_blockio_weight = ul;
-                        u->cgroup_realized_mask &= ~CGROUP_BLKIO;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_BLKIO;
                         unit_write_drop_in_private_format(u, mode, name, "StartupBlockIOWeight=%lu", ul);
                 }
 
@@ -427,7 +427,7 @@ int bus_cgroup_set_property(
                                                 cgroup_context_free_blockio_device_bandwidth(c, a);
                         }
 
-                        u->cgroup_realized_mask &= ~CGROUP_BLKIO;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_BLKIO;
 
                         f = open_memstream(&buf, &size);
                         if (!f)
@@ -510,7 +510,7 @@ int bus_cgroup_set_property(
                                         cgroup_context_free_blockio_device_weight(c, c->blockio_device_weights);
                         }
 
-                        u->cgroup_realized_mask &= ~CGROUP_BLKIO;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_BLKIO;
 
                         f = open_memstream(&buf, &size);
                         if (!f)
@@ -535,7 +535,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->memory_accounting = b;
-                        u->cgroup_realized_mask &= ~CGROUP_MEMORY;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_MEMORY;
                         unit_write_drop_in_private(u, mode, name, b ? "MemoryAccounting=yes" : "MemoryAccounting=no");
                 }
 
@@ -550,7 +550,7 @@ int bus_cgroup_set_property(
 
                 if (mode != UNIT_CHECK) {
                         c->memory_limit = limit;
-                        u->cgroup_realized_mask &= ~CGROUP_MEMORY;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_MEMORY;
                         unit_write_drop_in_private_format(u, mode, name, "%s=%" PRIu64, name, limit);
                 }
 
@@ -572,7 +572,7 @@ int bus_cgroup_set_property(
                         char *buf;
 
                         c->device_policy = p;
-                        u->cgroup_realized_mask &= ~CGROUP_DEVICE;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_DEVICE;
 
                         buf = strjoina("DevicePolicy=", policy);
                         unit_write_drop_in_private(u, mode, name, buf);
@@ -651,7 +651,7 @@ int bus_cgroup_set_property(
                                         cgroup_context_free_device_allow(c, c->device_allow);
                         }
 
-                        u->cgroup_realized_mask &= ~CGROUP_DEVICE;
+                        u->cgroup_realized_mask &= ~CGROUP_MASK_DEVICE;
 
                         f = open_memstream(&buf, &size);
                         if (!f)
diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index 1e6291e762..31016b6c4a 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -25,6 +25,7 @@
 #include "cgroup-util.h"
 #include "strv.h"
 #include "bus-common-errors.h"
+#include "special.h"
 #include "dbus.h"
 #include "dbus-unit.h"
 
@@ -973,6 +974,8 @@ static int bus_unit_set_transient_property(
                         return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "The slice property is only available for units with control groups.");
                 if (u->type == UNIT_SLICE)
                         return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Slice may not be set for slice units.");
+                if (unit_has_name(u, SPECIAL_INIT_SCOPE))
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Cannot set slice for init.scope");
 
                 r = sd_bus_message_read(message, "s", &s);
                 if (r < 0)
diff --git a/src/core/execute.h b/src/core/execute.h
index 8d14fe23d0..a750246a89 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -214,7 +214,7 @@ struct ExecParameters {
         bool apply_tty_stdin;
         bool confirm_spawn;
         bool selinux_context_net;
-        CGroupControllerMask cgroup_supported;
+        CGroupMask cgroup_supported;
         const char *cgroup_path;
         bool cgroup_delegate;
         const char *runtime_prefix;
diff --git a/src/core/manager.c b/src/core/manager.c
index 14f069ba97..c3327e37f5 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -568,7 +568,9 @@ int manager_new(ManagerRunningAs running_as, bool test_run, Manager **_m) {
 
         m->idle_pipe[0] = m->idle_pipe[1] = m->idle_pipe[2] = m->idle_pipe[3] = -1;
 
-        m->pin_cgroupfs_fd = m->notify_fd = m->signal_fd = m->time_change_fd = m->dev_autofs_fd = m->private_listen_fd = m->kdbus_fd = m->utab_inotify_fd = -1;
+        m->pin_cgroupfs_fd = m->notify_fd = m->signal_fd = m->time_change_fd =
+                m->dev_autofs_fd = m->private_listen_fd = m->kdbus_fd = m->utab_inotify_fd =
+                m->cgroup_inotify_fd = -1;
         m->current_job_id = 1; /* start as id #1, so that we can leave #0 around as "null-like" value */
 
         m->ask_password_inotify_fd = -1;
@@ -2722,7 +2724,7 @@ void manager_check_finished(Manager *m) {
 
         SET_FOREACH(u, m->startup_units, i)
                 if (u->cgroup_path)
-                        cgroup_context_apply(unit_get_cgroup_context(u), unit_get_cgroup_mask(u), u->cgroup_path, manager_state(m));
+                        cgroup_context_apply(unit_get_cgroup_context(u), unit_get_own_mask(u), u->cgroup_path, manager_state(m));
 }
 
 static int create_generator_dir(Manager *m, char **generator, const char *name) {
diff --git a/src/core/manager.h b/src/core/manager.h
index 3f7fa24e58..9956cb7700 100644
--- a/src/core/manager.h
+++ b/src/core/manager.h
@@ -215,16 +215,22 @@ struct Manager {
 
         /* Data specific to the cgroup subsystem */
         Hashmap *cgroup_unit;
-        CGroupControllerMask cgroup_supported;
+        CGroupMask cgroup_supported;
         char *cgroup_root;
 
-        int gc_marker;
-        unsigned n_in_gc_queue;
+        /* Notifications from cgroups, when the unified hierarchy is
+         * used is done via inotify. */
+        int cgroup_inotify_fd;
+        sd_event_source *cgroup_inotify_event_source;
+        Hashmap *cgroup_inotify_wd_unit;
 
         /* Make sure the user cannot accidentally unmount our cgroup
          * file system */
         int pin_cgroupfs_fd;
 
+        int gc_marker;
+        unsigned n_in_gc_queue;
+
         /* Flags */
         ManagerRunningAs running_as;
         ManagerExitCode exit_code:5;
diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c
index 1782d40720..c6f3569915 100644
--- a/src/core/mount-setup.c
+++ b/src/core/mount-setup.c
@@ -93,12 +93,14 @@ static const MountPoint mount_table[] = {
 #endif
         { "tmpfs",       "/run",                      "tmpfs",      "mode=755",                MS_NOSUID|MS_NODEV|MS_STRICTATIME,
           NULL,          MNT_FATAL|MNT_IN_CONTAINER },
+        { "cgroup",      "/sys/fs/cgroup",            "cgroup",     "__DEVEL__sane_behavior",  MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          cg_is_unified_wanted, MNT_FATAL|MNT_IN_CONTAINER },
         { "tmpfs",       "/sys/fs/cgroup",            "tmpfs",      "mode=755",                MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME,
-          NULL,          MNT_FATAL|MNT_IN_CONTAINER },
+          cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
         { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd,xattr", MS_NOSUID|MS_NOEXEC|MS_NODEV,
-          NULL,          MNT_IN_CONTAINER           },
+          cg_is_legacy_wanted, MNT_IN_CONTAINER           },
         { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd",       MS_NOSUID|MS_NOEXEC|MS_NODEV,
-          NULL,          MNT_FATAL|MNT_IN_CONTAINER },
+          cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
         { "pstore",      "/sys/fs/pstore",            "pstore",     NULL,                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           NULL,          MNT_NONE                   },
 #ifdef ENABLE_EFI
@@ -217,6 +219,9 @@ int mount_cgroup_controllers(char ***join_controllers) {
         _cleanup_set_free_free_ Set *controllers = NULL;
         int r;
 
+        if (!cg_is_legacy_wanted())
+                return 0;
+
         /* Mount all available cgroup controllers that are built into the kernel. */
 
         controllers = set_new(&string_hash_ops);
diff --git a/src/core/scope.c b/src/core/scope.c
index 1e94d63561..44cd324f58 100644
--- a/src/core/scope.c
+++ b/src/core/scope.c
@@ -22,12 +22,13 @@
 #include <errno.h>
 #include <unistd.h>
 
-#include "unit.h"
-#include "scope.h"
 #include "log.h"
-#include "dbus-scope.h"
+#include "strv.h"
 #include "special.h"
 #include "unit-name.h"
+#include "unit.h"
+#include "scope.h"
+#include "dbus-scope.h"
 #include "load-dropin.h"
 
 static const UnitActiveState state_translation_table[_SCOPE_STATE_MAX] = {
@@ -136,7 +137,9 @@ static int scope_verify(Scope *s) {
         if (UNIT(s)->load_state != UNIT_LOADED)
                 return 0;
 
-        if (set_isempty(UNIT(s)->pids) && UNIT(s)->manager->n_reloading <= 0) {
+        if (set_isempty(UNIT(s)->pids) &&
+            !manager_is_reloading_or_reexecuting(UNIT(s)->manager) <= 0 &&
+            !unit_has_name(UNIT(s), SPECIAL_INIT_SCOPE)) {
                 log_unit_error(UNIT(s), "Scope has no PIDs. Refusing.");
                 return -EINVAL;
         }
@@ -151,7 +154,7 @@ static int scope_load(Unit *u) {
         assert(s);
         assert(u->load_state == UNIT_STUB);
 
-        if (!u->transient && UNIT(s)->manager->n_reloading <= 0)
+        if (!u->transient && !manager_is_reloading_or_reexecuting(u->manager))
                 return -ENOENT;
 
         u->load_state = UNIT_LOADED;
@@ -279,6 +282,9 @@ static int scope_start(Unit *u) {
 
         assert(s);
 
+        if (unit_has_name(u, SPECIAL_INIT_SCOPE))
+                return -EPERM;
+
         if (s->state == SCOPE_FAILED)
                 return -EPERM;
 
@@ -289,7 +295,7 @@ static int scope_start(Unit *u) {
 
         assert(s->state == SCOPE_DEAD);
 
-        if (!u->transient && UNIT(s)->manager->n_reloading <= 0)
+        if (!u->transient && !manager_is_reloading_or_reexecuting(u->manager))
                 return -ENOENT;
 
         (void) unit_realize_cgroup(u);
@@ -464,6 +470,9 @@ static int scope_dispatch_timer(sd_event_source *source, usec_t usec, void *user
 int scope_abandon(Scope *s) {
         assert(s);
 
+        if (unit_has_name(UNIT(s), SPECIAL_INIT_SCOPE))
+                return -EPERM;
+
         if (!IN_SET(s->state, SCOPE_RUNNING, SCOPE_ABANDONED))
                 return -ESTALE;
 
@@ -499,6 +508,48 @@ _pure_ static const char *scope_sub_state_to_string(Unit *u) {
         return scope_state_to_string(SCOPE(u)->state);
 }
 
+static int scope_enumerate(Manager *m) {
+        Unit *u;
+        int r;
+
+        assert(m);
+
+        /* Let's unconditionally add the "init.scope" special unit
+         * that encapsulates PID 1. Note that PID 1 already is in the
+         * cgroup for this, we hence just need to allocate the object
+         * for it and that's it. */
+
+        u = manager_get_unit(m, SPECIAL_INIT_SCOPE);
+        if (!u) {
+                u = unit_new(m, sizeof(Scope));
+                if (!u)
+                        return log_oom();
+
+                r = unit_add_name(u, SPECIAL_INIT_SCOPE);
+                if (r < 0)  {
+                        unit_free(u);
+                        return log_error_errno(r, "Failed to add init.scope name");
+                }
+        }
+
+        u->transient = true;
+        u->default_dependencies = false;
+        u->no_gc = true;
+        SCOPE(u)->deserialized_state = SCOPE_RUNNING;
+        SCOPE(u)->kill_context.kill_signal = SIGRTMIN+14;
+
+        /* Prettify things, if we can. */
+        if (!u->description)
+                u->description = strdup("System and Service Manager");
+        if (!u->documentation)
+                (void) strv_extend(&u->documentation, "man:systemd(1)");
+
+        unit_add_to_load_queue(u);
+        unit_add_to_dbus_queue(u);
+
+        return 0;
+}
+
 static const char* const scope_state_table[_SCOPE_STATE_MAX] = {
         [SCOPE_DEAD] = "dead",
         [SCOPE_RUNNING] = "running",
@@ -565,5 +616,7 @@ const UnitVTable scope_vtable = {
         .bus_set_property = bus_scope_set_property,
         .bus_commit_properties = bus_scope_commit_properties,
 
-        .can_transient = true
+        .can_transient = true,
+
+        .enumerate = scope_enumerate,
 };
diff --git a/src/core/service.c b/src/core/service.c
index 5a0a3aa867..292fe50de8 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -767,7 +767,7 @@ static int service_load_pid_file(Service *s, bool may_warn) {
 }
 
 static int service_search_main_pid(Service *s) {
-        pid_t pid;
+        pid_t pid = 0;
         int r;
 
         assert(s);
@@ -782,9 +782,9 @@ static int service_search_main_pid(Service *s) {
 
         assert(s->main_pid <= 0);
 
-        pid = unit_search_main_pid(UNIT(s));
-        if (pid <= 0)
-                return -ENOENT;
+        r = unit_search_main_pid(UNIT(s), &pid);
+        if (r < 0)
+                return r;
 
         log_unit_debug(UNIT(s), "Main PID guessed: "PID_FMT, pid);
         r = service_set_main_pid(s, pid);
@@ -860,7 +860,7 @@ static void service_set_state(Service *s, ServiceState state) {
         /* For the inactive states unit_notify() will trim the cgroup,
          * but for exit we have to do that ourselves... */
         if (state == SERVICE_EXITED && UNIT(s)->manager->n_reloading <= 0)
-                unit_destroy_cgroup_if_empty(UNIT(s));
+                unit_prune_cgroup(UNIT(s));
 
         /* For remain_after_exit services, let's see if we can "release" the
          * hold on the console, since unit_notify() only does that in case of
@@ -2644,7 +2644,7 @@ static void service_sigchld_event(Unit *u, pid_t pid, int code, int status) {
                                                 break;
                                         }
                                 } else
-                                        service_search_main_pid(s);
+                                        (void) service_search_main_pid(s);
 
                                 service_enter_start_post(s);
                                 break;
@@ -2666,7 +2666,7 @@ static void service_sigchld_event(Unit *u, pid_t pid, int code, int status) {
                                                 break;
                                         }
                                 } else
-                                        service_search_main_pid(s);
+                                        (void) service_search_main_pid(s);
 
                                 service_enter_running(s, SERVICE_SUCCESS);
                                 break;
@@ -2674,7 +2674,7 @@ static void service_sigchld_event(Unit *u, pid_t pid, int code, int status) {
                         case SERVICE_RELOAD:
                                 if (f == SERVICE_SUCCESS) {
                                         service_load_pid_file(s, true);
-                                        service_search_main_pid(s);
+                                        (void) service_search_main_pid(s);
                                 }
 
                                 s->reload_result = f;
diff --git a/src/core/slice.c b/src/core/slice.c
index 7442d23391..b414462066 100644
--- a/src/core/slice.c
+++ b/src/core/slice.c
@@ -21,12 +21,13 @@
 
 #include <errno.h>
 
-#include "unit.h"
-#include "slice.h"
 #include "log.h"
-#include "dbus-slice.h"
+#include "strv.h"
 #include "special.h"
 #include "unit-name.h"
+#include "unit.h"
+#include "slice.h"
+#include "dbus-slice.h"
 
 static const UnitActiveState state_translation_table[_SLICE_STATE_MAX] = {
         [SLICE_DEAD] = UNIT_INACTIVE,
@@ -252,6 +253,40 @@ _pure_ static const char *slice_sub_state_to_string(Unit *u) {
         return slice_state_to_string(SLICE(u)->state);
 }
 
+static int slice_enumerate(Manager *m) {
+        Unit *u;
+        int r;
+
+        assert(m);
+
+        u = manager_get_unit(m, SPECIAL_ROOT_SLICE);
+        if (!u) {
+                u = unit_new(m, sizeof(Slice));
+                if (!u)
+                        return log_oom();
+
+                r = unit_add_name(u, SPECIAL_ROOT_SLICE);
+                if (r < 0) {
+                        unit_free(u);
+                        return log_error_errno(r, "Failed to add -.slice name");
+                }
+        }
+
+        u->default_dependencies = false;
+        u->no_gc = true;
+        SLICE(u)->deserialized_state = SLICE_ACTIVE;
+
+        if (!u->description)
+                u->description = strdup("Root Slice");
+        if (!u->documentation)
+                (void) strv_extend(&u->documentation, "man:systemd.special(7)");
+
+        unit_add_to_load_queue(u);
+        unit_add_to_dbus_queue(u);
+
+        return 0;
+}
+
 static const char* const slice_state_table[_SLICE_STATE_MAX] = {
         [SLICE_DEAD] = "dead",
         [SLICE_ACTIVE] = "active"
@@ -293,6 +328,8 @@ const UnitVTable slice_vtable = {
         .bus_set_property = bus_slice_set_property,
         .bus_commit_properties = bus_slice_commit_properties,
 
+        .enumerate = slice_enumerate,
+
         .status_message_formats = {
                 .finished_start_job = {
                         [JOB_DONE]       = "Created slice %s.",
diff --git a/src/core/unit.c b/src/core/unit.c
index 34d3adcd3b..8c07c6140d 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -91,6 +91,7 @@ Unit *unit_new(Manager *m, size_t size) {
         u->unit_file_state = _UNIT_FILE_STATE_INVALID;
         u->unit_file_preset = -1;
         u->on_failure_job_mode = JOB_REPLACE;
+        u->cgroup_inotify_wd = -1;
 
         RATELIMIT_INIT(u->auto_stop_ratelimit, 10 * USEC_PER_SEC, 16);
 
@@ -525,10 +526,7 @@ void unit_free(Unit *u) {
         if (u->in_cgroup_queue)
                 LIST_REMOVE(cgroup_queue, u->manager->cgroup_queue, u);
 
-        if (u->cgroup_path) {
-                hashmap_remove(u->manager->cgroup_unit, u->cgroup_path);
-                free(u->cgroup_path);
-        }
+        unit_release_cgroup(u);
 
         manager_update_failed_units(u->manager, u, false);
         set_remove(u->manager->startup_units, u);
@@ -1801,7 +1799,7 @@ void unit_notify(Unit *u, UnitActiveState os, UnitActiveState ns, bool reload_su
 
         /* Make sure the cgroup is always removed when we become inactive */
         if (UNIT_IS_INACTIVE_OR_FAILED(ns))
-                unit_destroy_cgroup_if_empty(u);
+                unit_prune_cgroup(u);
 
         /* Note that this doesn't apply to RemainAfterExit services exiting
          * successfully, since there's no change of state in that case. Which is
@@ -2028,70 +2026,7 @@ void unit_unwatch_all_pids(Unit *u) {
         while (!set_isempty(u->pids))
                 unit_unwatch_pid(u, PTR_TO_LONG(set_first(u->pids)));
 
-        set_free(u->pids);
-        u->pids = NULL;
-}
-
-static int unit_watch_pids_in_path(Unit *u, const char *path) {
-        _cleanup_closedir_ DIR *d = NULL;
-        _cleanup_fclose_ FILE *f = NULL;
-        int ret = 0, r;
-
-        assert(u);
-        assert(path);
-
-        /* Adds all PIDs from a specific cgroup path to the set of PIDs we watch. */
-
-        r = cg_enumerate_processes(SYSTEMD_CGROUP_CONTROLLER, path, &f);
-        if (r >= 0) {
-                pid_t pid;
-
-                while ((r = cg_read_pid(f, &pid)) > 0) {
-                        r = unit_watch_pid(u, pid);
-                        if (r < 0 && ret >= 0)
-                                ret = r;
-                }
-                if (r < 0 && ret >= 0)
-                        ret = r;
-
-        } else if (ret >= 0)
-                ret = r;
-
-        r = cg_enumerate_subgroups(SYSTEMD_CGROUP_CONTROLLER, path, &d);
-        if (r >= 0) {
-                char *fn;
-
-                while ((r = cg_read_subgroup(d, &fn)) > 0) {
-                        _cleanup_free_ char *p = NULL;
-
-                        p = strjoin(path, "/", fn, NULL);
-                        free(fn);
-
-                        if (!p)
-                                return -ENOMEM;
-
-                        r = unit_watch_pids_in_path(u, p);
-                        if (r < 0 && ret >= 0)
-                                ret = r;
-                }
-                if (r < 0 && ret >= 0)
-                        ret = r;
-
-        } else if (ret >= 0)
-                ret = r;
-
-        return ret;
-}
-
-int unit_watch_all_pids(Unit *u) {
-        assert(u);
-
-        /* Adds all PIDs from our cgroup to the set of PIDs we watch */
-
-        if (!u->cgroup_path)
-                return -ENOENT;
-
-        return unit_watch_pids_in_path(u, u->cgroup_path);
+        u->pids = set_free(u->pids);
 }
 
 void unit_tidy_watch_pids(Unit *u, pid_t except1, pid_t except2) {
@@ -2400,31 +2335,6 @@ char *unit_dbus_path(Unit *u) {
         return unit_dbus_path_from_name(u->id);
 }
 
-char *unit_default_cgroup_path(Unit *u) {
-        _cleanup_free_ char *escaped = NULL, *slice = NULL;
-        int r;
-
-        assert(u);
-
-        if (unit_has_name(u, SPECIAL_ROOT_SLICE))
-                return strdup(u->manager->cgroup_root);
-
-        if (UNIT_ISSET(u->slice) && !unit_has_name(UNIT_DEREF(u->slice), SPECIAL_ROOT_SLICE)) {
-                r = cg_slice_to_path(UNIT_DEREF(u->slice)->id, &slice);
-                if (r < 0)
-                        return NULL;
-        }
-
-        escaped = cg_escape(u->id);
-        if (!escaped)
-                return NULL;
-
-        if (slice)
-                return strjoin(u->manager->cgroup_root, "/", slice, "/", escaped, NULL);
-        else
-                return strjoin(u->manager->cgroup_root, "/", escaped, NULL);
-}
-
 int unit_set_slice(Unit *u, Unit *slice) {
         assert(u);
         assert(slice);
@@ -2447,6 +2357,10 @@ int unit_set_slice(Unit *u, Unit *slice) {
         if (slice->type != UNIT_SLICE)
                 return -EINVAL;
 
+        if (unit_has_name(u, SPECIAL_INIT_SCOPE) &&
+            !unit_has_name(slice, SPECIAL_ROOT_SLICE))
+                return -EPERM;
+
         if (UNIT_DEREF(u->slice) == slice)
                 return 0;
 
@@ -2495,7 +2409,7 @@ int unit_set_default_slice(Unit *u) {
                 slice_name = b;
         } else
                 slice_name =
-                        u->manager->running_as == MANAGER_SYSTEM
+                        u->manager->running_as == MANAGER_SYSTEM && !unit_has_name(u, SPECIAL_INIT_SCOPE)
                         ? SPECIAL_SYSTEM_SLICE
                         : SPECIAL_ROOT_SLICE;
 
@@ -2704,40 +2618,6 @@ void unit_serialize_item(Unit *u, FILE *f, const char *key, const char *value) {
         fprintf(f, "%s=%s\n", key, value);
 }
 
-static int unit_set_cgroup_path(Unit *u, const char *path) {
-        _cleanup_free_ char *p = NULL;
-        int r;
-
-        assert(u);
-
-        if (path) {
-                p = strdup(path);
-                if (!p)
-                        return -ENOMEM;
-        } else
-                p = NULL;
-
-        if (streq_ptr(u->cgroup_path, p))
-                return 0;
-
-        if (p) {
-                r = hashmap_put(u->manager->cgroup_unit, p, u);
-                if (r < 0)
-                        return r;
-        }
-
-        if (u->cgroup_path) {
-                log_unit_debug(u, "Changing cgroup path from %s to %s.", u->cgroup_path, strna(p));
-                hashmap_remove(u->manager->cgroup_unit, u->cgroup_path);
-                free(u->cgroup_path);
-        }
-
-        u->cgroup_path = p;
-        p = NULL;
-
-        return 0;
-}
-
 int unit_deserialize(Unit *u, FILE *f, FDSet *fds) {
         ExecRuntime **rt = NULL;
         size_t offset;
@@ -2868,6 +2748,8 @@ int unit_deserialize(Unit *u, FILE *f, FDSet *fds) {
                         if (r < 0)
                                 log_unit_debug_errno(u, r, "Failed to set cgroup path %s, ignoring: %m", v);
 
+                        (void) unit_watch_cgroup(u);
+
                         continue;
                 } else if (streq(l, "cgroup-realized")) {
                         int b;
@@ -3600,18 +3482,22 @@ int unit_kill_context(
 
                 } else if (r > 0) {
 
-                        /* FIXME: For now, we will not wait for the
-                         * cgroup members to die if we are running in
-                         * a container or if this is a delegation
-                         * unit, simply because cgroup notification is
-                         * unreliable in these cases. It doesn't work
-                         * at all in containers, and outside of
-                         * containers it can be confused easily by
-                         * left-over directories in the cgroup --
-                         * which however should not exist in
-                         * non-delegated units. */
-
-                        if  (detect_container(NULL) == 0 && !unit_cgroup_delegate(u))
+                        /* FIXME: For now, on the legacy hierarchy, we
+                         * will not wait for the cgroup members to die
+                         * if we are running in a container or if this
+                         * is a delegation unit, simply because cgroup
+                         * notification is unreliable in these
+                         * cases. It doesn't work at all in
+                         * containers, and outside of containers it
+                         * can be confused easily by left-over
+                         * directories in the cgroup -- which however
+                         * should not exist in non-delegated units. On
+                         * the unified hierarchy that's different,
+                         * there we get proper events. Hence rely on
+                         * them.*/
+
+                        if  (cg_unified() > 0 ||
+                             (detect_container(NULL) == 0 && !unit_cgroup_delegate(u)))
                                 wait_for_exit = true;
 
                         if (c->send_sighup && k != KILL_KILL) {
diff --git a/src/core/unit.h b/src/core/unit.h
index bc26653247..3c7684411b 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -184,9 +184,10 @@ struct Unit {
 
         /* Counterparts in the cgroup filesystem */
         char *cgroup_path;
-        CGroupControllerMask cgroup_realized_mask;
-        CGroupControllerMask cgroup_subtree_mask;
-        CGroupControllerMask cgroup_members_mask;
+        CGroupMask cgroup_realized_mask;
+        CGroupMask cgroup_subtree_mask;
+        CGroupMask cgroup_members_mask;
+        int cgroup_inotify_wd;
 
         /* How to start OnFailure units */
         JobMode on_failure_job_mode;
@@ -522,7 +523,6 @@ void unit_notify(Unit *u, UnitActiveState os, UnitActiveState ns, bool reload_su
 
 int unit_watch_pid(Unit *u, pid_t pid);
 void unit_unwatch_pid(Unit *u, pid_t pid);
-int unit_watch_all_pids(Unit *u);
 void unit_unwatch_all_pids(Unit *u);
 
 void unit_tidy_watch_pids(Unit *u, pid_t except1, pid_t except2);
@@ -567,8 +567,6 @@ bool unit_active_or_pending(Unit *u);
 
 int unit_add_default_target_dependency(Unit *u, Unit *target);
 
-char *unit_default_cgroup_path(Unit *u);
-
 void unit_start_on_failure(Unit *u);
 void unit_trigger_notify(Unit *u);