Revert "memcg: support priority for oom"

This reverts commit 8200f0ca.

include/linux/memcontrol.h

@@ -296,12 +296,6 @@ struct mem_cgroup {
 	bool			tcpmem_active;
 	int			tcpmem_pressure;
 
-#ifdef CONFIG_MEMCG_QOS
-	/* Currently support 0 and -1.
-	 * in the future it can expand to other value.
-	 */
-	int	memcg_priority;
-#endif
 #ifdef CONFIG_MEMCG_KMEM
         /* Index in the kmem_cache->memcg_params.memcg_caches array */
 	int kmemcg_id;
@@ -333,12 +327,6 @@ struct mem_cgroup {
 	/* WARNING: nodeinfo must be the last member here */
 };
 
-#ifdef CONFIG_MEMCG_QOS
-bool memcg_low_priority_scan_tasks(int (*)(struct task_struct *, void *),
-				   void *);
-void memcg_print_bad_task(void *arg, int ret);
-#endif
-
 /*
  * size of first charge trial. "32" comes from vmscan.c's magic value.
  * TODO: maybe necessary to use big numbers in big irons.

mm/Kconfig

@@ -516,18 +516,6 @@ config USERSWAP
 	  Support for User Swap. This is based on userfaultfd. We can implement
 	  our own swapout and swapin functions in usersapce.
 
-config MEMCG_QOS
-	bool "Enable Memory Cgroup Priority"
-	depends on MEMCG
-	depends on X86 || ARM64
-	default y
-	help
-	  MEMCG_QOS means that we first kill the process from the low priority
-	  memcg if OOM occurs. If the process is not found, then fallback to
-	  normal handle.
-
-	  If unsure, say "n".
-
 config CMA
 	bool "Contiguous Memory Allocator"
 	depends on HAVE_MEMBLOCK && MMU

mm/memcontrol.c

@@ -1235,9 +1235,6 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
 			break;
 		}
 	}
-#ifdef CONFIG_MEMCG_QOS
-	memcg_print_bad_task(arg, ret);
-#endif
 	return ret;
 }
 
@@ -3639,119 +3636,6 @@ static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
 }
 #endif
 
-#ifdef CONFIG_MEMCG_QOS
-static void memcg_qos_init(struct mem_cgroup *memcg)
-{
-	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
-
-	if (!parent)
-		return;
-
-	if (parent->memcg_priority && parent->use_hierarchy)
-		memcg->memcg_priority = parent->memcg_priority;
-}
-
-static s64 memcg_qos_read(struct cgroup_subsys_state *css,
-				      struct cftype *cft)
-{
-	return mem_cgroup_from_css(css)->memcg_priority;
-}
-
-static int memcg_qos_write(struct cgroup_subsys_state *css,
-				       struct cftype *cft, s64 val)
-{
-	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
-
-	if (val >= 0)
-		memcg->memcg_priority = 0;
-	else
-		memcg->memcg_priority = -1;
-
-	return 0;
-}
-
-static struct mem_cgroup *memcg_find_max_usage(struct mem_cgroup *last)
-{
-	struct mem_cgroup *iter, *max_memcg = NULL;
-	struct cgroup_subsys_state *css;
-	unsigned long usage, max_usage = 0;
-
-	rcu_read_lock();
-	css_for_each_descendant_pre(css, &root_mem_cgroup->css) {
-		iter = mem_cgroup_from_css(css);
-
-		if (!iter->memcg_priority || iter == root_mem_cgroup ||
-			iter == last)
-			continue;
-
-		usage = mem_cgroup_usage(iter, false);
-		if (usage > max_usage) {
-			max_usage = usage;
-			max_memcg = iter;
-		}
-	}
-	rcu_read_unlock();
-
-	return max_memcg;
-}
-
-bool memcg_low_priority_scan_tasks(int (*fn)(struct task_struct *, void *),
-				   void *arg)
-{
-	struct mem_cgroup *max, *last = NULL;
-	struct oom_control *oc = arg;
-	struct css_task_iter it;
-	struct task_struct *task;
-	int ret = 0;
-	bool retry = true;
-
-retry:
-	max = memcg_find_max_usage(last);
-	if (!max)
-		return false;
-
-	css_task_iter_start(&max->css, CSS_TASK_ITER_PROCS, &it);
-	while (!ret && (task = css_task_iter_next(&it))) {
-		if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
-			pr_info("task %s is dying.\n", task->comm);
-			continue;
-		}
-
-		ret = fn(task, arg);
-	}
-	css_task_iter_end(&it);
-
-	if (ret)
-		return false;
-
-	if (!oc->chosen && retry) {
-		last = max;
-		retry = false;
-		goto retry;
-	}
-
-	if (oc->chosen)
-		pr_info("The bad task [%d:%s] is from low-priority memcg.\n",
-				oc->chosen->pid, oc->chosen->comm);
-
-	return oc->chosen ? true : false;
-}
-
-void memcg_print_bad_task(void *arg, int ret)
-{
-	struct oom_control *oc = arg;
-
-	if (!ret && oc->chosen) {
-		struct mem_cgroup *memcg;
-
-		memcg = mem_cgroup_from_task(oc->chosen);
-		if (memcg->memcg_priority)
-			pr_info("The bad task [%d:%s] is from low-priority memcg.\n",
-				oc->chosen->pid, oc->chosen->comm);
-	}
-}
-#endif
-
 #ifdef CONFIG_NUMA
 
 #define LRU_ALL_FILE (BIT(LRU_INACTIVE_FILE) | BIT(LRU_ACTIVE_FILE))
@@ -4707,13 +4591,6 @@ static struct cftype mem_cgroup_legacy_files[] = {
 	{
 		.name = "pressure_level",
 	},
-#ifdef CONFIG_MEMCG_QOS
-	{
-		.name = "qos_level",
-		.read_s64 = memcg_qos_read,
-		.write_s64 = memcg_qos_write,
-	},
-#endif
 #ifdef CONFIG_NUMA
 	{
 		.name = "numa_stat",
@@ -5065,10 +4942,6 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 		return -ENOMEM;
 	}
 
-#ifdef CONFIG_MEMCG_QOS
-	memcg_qos_init(memcg);
-#endif
-
 	/* Online state pins memcg ID, memcg ID pins CSS */
 	atomic_set(&memcg->id.ref, 1);
 	css_get(css);

mm/oom_kill.c

@@ -318,49 +318,6 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 	return CONSTRAINT_NONE;
 }
 
-#ifdef CONFIG_MEMCG_QOS
-/**
- * We choose the task in low-priority memcg firstly. For the same state, we
- * choose the task with the highest number of 'points'.
- */
-static bool oom_next_task(struct task_struct *task, struct oom_control *oc,
-			unsigned long points)
-{
-	struct mem_cgroup *cur_memcg;
-	struct mem_cgroup *oc_memcg;
-
-
-	if (!points)
-		return true;
-
-	if (!oc->chosen)
-		return false;
-
-	oc_memcg = mem_cgroup_from_task(oc->chosen);
-	cur_memcg = mem_cgroup_from_task(task);
-
-	if (cur_memcg->memcg_priority == oc_memcg->memcg_priority) {
-		if (points < oc->chosen_points)
-			return true;
-		return false;
-	}
-	/* if oc is low-priority, so skip the task */
-	if (oc_memcg->memcg_priority)
-		return true;
-
-	return false;
-}
-#else
-static inline bool oom_next_task(struct task_struct *task,
-				struct oom_control *oc, unsigned long points)
-{
-	if (!points || points < oc->chosen_points)
-		return true;
-
-	return false;
-}
-#endif
-
 static int oom_evaluate_task(struct task_struct *task, void *arg)
 {
 	struct oom_control *oc = arg;
@@ -391,7 +348,7 @@ static int oom_evaluate_task(struct task_struct *task, void *arg)
 	}
 
 	points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
-	if (oom_next_task(task, oc, points))
+	if (!points || points < oc->chosen_points)
 		goto next;
 
 select:
@@ -420,10 +377,6 @@ static void select_bad_process(struct oom_control *oc)
 	else {
 		struct task_struct *p;
 
-#ifdef CONFIG_MEMCG_QOS
-		if (memcg_low_priority_scan_tasks(oom_evaluate_task, oc))
-			return;
-#endif
 		rcu_read_lock();
 		for_each_process(p)
 			if (oom_evaluate_task(p, oc))