system. It might be too late to consult with vmstat or any other
statistics, so it's advisable to take an immediate action.
-The events are propagated upward until the event is handled, i.e. the
-events are not pass-through. Here is what this means: for example you have
-three cgroups: A->B->C. Now you set up an event listener on cgroups A, B
-and C, and suppose group C experiences some pressure. In this situation,
-only group C will receive the notification, i.e. groups A and B will not
-receive it. This is done to avoid excessive "broadcasting" of messages,
-which disturbs the system and which is especially bad if we are low on
-memory or thrashing. So, organize the cgroups wisely, or propagate the
-events manually (or, ask us to implement the pass-through events,
-explaining why would you need them.)
+By default, events are propagated upward until the event is handled, i.e. the
+events are not pass-through. For example, you have three cgroups: A->B->C. Now
+you set up an event listener on cgroups A, B and C, and suppose group C
+experiences some pressure. In this situation, only group C will receive the
+notification, i.e. groups A and B will not receive it. This is done to avoid
+excessive "broadcasting" of messages, which disturbs the system and which is
+especially bad if we are low on memory or thrashing. Group B, will receive
+notification only if there are no event listers for group C.
+
+There are three optional modes that specify different propagation behavior:
+
+ - "default": this is the default behavior specified above. This mode is the
+ same as omitting the optional mode parameter, preserved by backwards
+ compatibility.
+
+ - "hierarchy": events always propagate up to the root, similar to the default
+ behavior, except that propagation continues regardless of whether there are
+ event listeners at each level, with the "hierarchy" mode. In the above
+ example, groups A, B, and C will receive notification of memory pressure.
+
+ - "local": events are pass-through, i.e. they only receive notifications when
+ memory pressure is experienced in the memcg for which the notification is
+ registered. In the above example, group C will receive notification if
+ registered for "local" notification and the group experiences memory
+ pressure. However, group B will never receive notification, regardless if
+ there is an event listener for group C or not, if group B is registered for
+ local notification.
+
+The level and event notification mode ("hierarchy" or "local", if necessary) are
+specified by a comma-delimited string, i.e. "low,hierarchy" specifies
+hierarchical, pass-through, notification for all ancestor memcgs. Notification
+that is the default, non pass-through behavior, does not specify a mode.
+"medium,local" specifies pass-through notification for the medium level.
The file memory.pressure_level is only used to setup an eventfd. To
register a notification, an application must:
- create an eventfd using eventfd(2);
- open memory.pressure_level;
-- write string like "<event_fd> <fd of memory.pressure_level> <level>"
+- write string as "<event_fd> <fd of memory.pressure_level> <level[,mode]>"
to cgroup.event_control.
Application will be notified through eventfd when memory pressure is at
# cd /sys/fs/cgroup/memory/
# mkdir foo
# cd foo
- # cgroup_event_listener memory.pressure_level low &
+ # cgroup_event_listener memory.pressure_level low,hierarchy &
# echo 8000000 > memory.limit_in_bytes
# echo 8000000 > memory.memsw.limit_in_bytes
# echo $$ > tasks
VMPRESSURE_NUM_LEVELS,
};
+enum vmpressure_modes {
+ VMPRESSURE_NO_PASSTHROUGH = 0,
+ VMPRESSURE_HIERARCHY,
+ VMPRESSURE_LOCAL,
+ VMPRESSURE_NUM_MODES,
+};
+
static const char * const vmpressure_str_levels[] = {
[VMPRESSURE_LOW] = "low",
[VMPRESSURE_MEDIUM] = "medium",
[VMPRESSURE_CRITICAL] = "critical",
};
+static const char * const vmpressure_str_modes[] = {
+ [VMPRESSURE_NO_PASSTHROUGH] = "default",
+ [VMPRESSURE_HIERARCHY] = "hierarchy",
+ [VMPRESSURE_LOCAL] = "local",
+};
+
static enum vmpressure_levels vmpressure_level(unsigned long pressure)
{
if (pressure >= vmpressure_level_critical)
struct vmpressure_event {
struct eventfd_ctx *efd;
enum vmpressure_levels level;
+ enum vmpressure_modes mode;
struct list_head node;
};
static bool vmpressure_event(struct vmpressure *vmpr,
- enum vmpressure_levels level)
+ const enum vmpressure_levels level,
+ bool ancestor, bool signalled)
{
struct vmpressure_event *ev;
- bool signalled = false;
+ bool ret = false;
mutex_lock(&vmpr->events_lock);
-
list_for_each_entry(ev, &vmpr->events, node) {
- if (level >= ev->level) {
- eventfd_signal(ev->efd, 1);
- signalled = true;
- }
+ if (ancestor && ev->mode == VMPRESSURE_LOCAL)
+ continue;
+ if (signalled && ev->mode == VMPRESSURE_NO_PASSTHROUGH)
+ continue;
+ if (level < ev->level)
+ continue;
+ eventfd_signal(ev->efd, 1);
+ ret = true;
}
-
mutex_unlock(&vmpr->events_lock);
- return signalled;
+ return ret;
}
static void vmpressure_work_fn(struct work_struct *work)
unsigned long scanned;
unsigned long reclaimed;
enum vmpressure_levels level;
+ bool ancestor = false;
+ bool signalled = false;
spin_lock(&vmpr->sr_lock);
/*
level = vmpressure_calc_level(scanned, reclaimed);
do {
- if (vmpressure_event(vmpr, level))
- break;
- /*
- * If not handled, propagate the event upward into the
- * hierarchy.
- */
+ if (vmpressure_event(vmpr, level, ancestor, signalled))
+ signalled = true;
+ ancestor = true;
} while ((vmpr = vmpressure_parent(vmpr)));
}
vmpressure(gfp, memcg, true, vmpressure_win, 0);
}
+static enum vmpressure_levels str_to_level(const char *arg)
+{
+ enum vmpressure_levels level;
+
+ for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++)
+ if (!strcmp(vmpressure_str_levels[level], arg))
+ return level;
+ return -1;
+}
+
+static enum vmpressure_modes str_to_mode(const char *arg)
+{
+ enum vmpressure_modes mode;
+
+ for (mode = 0; mode < VMPRESSURE_NUM_MODES; mode++)
+ if (!strcmp(vmpressure_str_modes[mode], arg))
+ return mode;
+ return -1;
+}
+
+#define MAX_VMPRESSURE_ARGS_LEN (strlen("critical") + strlen("hierarchy") + 2)
+
/**
* vmpressure_register_event() - Bind vmpressure notifications to an eventfd
* @memcg: memcg that is interested in vmpressure notifications
* @eventfd: eventfd context to link notifications with
- * @args: event arguments (used to set up a pressure level threshold)
+ * @args: event arguments (pressure level threshold, optional mode)
*
* This function associates eventfd context with the vmpressure
* infrastructure, so that the notifications will be delivered to the
- * @eventfd. The @args parameter is a string that denotes pressure level
- * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
- * "critical").
+ * @eventfd. The @args parameter is a comma-delimited string that denotes a
+ * pressure level threshold (one of vmpressure_str_levels, i.e. "low", "medium",
+ * or "critical") and an optional mode (one of vmpressure_str_modes, i.e.
+ * "hierarchy" or "local").
*
* To be used as memcg event method.
*/
{
struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
struct vmpressure_event *ev;
- int level;
+ enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH;
+ enum vmpressure_levels level = -1;
+ char *spec, *spec_orig;
+ char *token;
+ int ret = 0;
+
+ spec_orig = spec = kzalloc(MAX_VMPRESSURE_ARGS_LEN + 1, GFP_KERNEL);
+ if (!spec) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ strncpy(spec, args, MAX_VMPRESSURE_ARGS_LEN);
- for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
- if (!strcmp(vmpressure_str_levels[level], args))
- break;
+ /* Find required level */
+ token = strsep(&spec, ",");
+ level = str_to_level(token);
+ if (level == -1) {
+ ret = -EINVAL;
+ goto out;
}
- if (level >= VMPRESSURE_NUM_LEVELS)
- return -EINVAL;
+ /* Find optional mode */
+ token = strsep(&spec, ",");
+ if (token) {
+ mode = str_to_mode(token);
+ if (mode == -1) {
+ ret = -EINVAL;
+ goto out;
+ }
+ }
ev = kzalloc(sizeof(*ev), GFP_KERNEL);
- if (!ev)
- return -ENOMEM;
+ if (!ev) {
+ ret = -ENOMEM;
+ goto out;
+ }
ev->efd = eventfd;
ev->level = level;
+ ev->mode = mode;
mutex_lock(&vmpr->events_lock);
list_add(&ev->node, &vmpr->events);
mutex_unlock(&vmpr->events_lock);
-
- return 0;
+out:
+ kfree(spec_orig);
+ return ret;
}
/**
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