Re: [PATCH 1/2] memcg, oom: provide more precise dump info while memcg oom happening

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On 11/08/2012 02:02 AM, David Rientjes wrote:
On Wed, 7 Nov 2012, Sha Zhengju wrote:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0eab7d5..2df5e72 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -118,6 +118,14 @@ static const char * const mem_cgroup_events_names[] = {
  	"pgmajfault",
  };

+static const char * const mem_cgroup_lru_names[] = {
+	"inactive_anon",
+	"active_anon",
+	"inactive_file",
+	"active_file",
+	"unevictable",
+};
+
  /*
   * Per memcg event counter is incremented at every pagein/pageout. With THP,
   * it will be incremated by the number of pages. This counter is used for
@@ -1501,8 +1509,59 @@ static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
  	spin_unlock_irqrestore(&memcg->move_lock, *flags);
  }

+#define K(x) ((x)<<  (PAGE_SHIFT-10))
+static void mem_cgroup_print_oom_stat(struct mem_cgroup *memcg)
+{
+	struct mem_cgroup *mi;
+	unsigned int i;
+
+	if (!memcg->use_hierarchy&&  memcg != root_mem_cgroup) {
+		for (i = 0; i<  MEM_CGROUP_STAT_NSTATS; i++) {
+			if (i == MEM_CGROUP_STAT_SWAP&&  !do_swap_account)
+				continue;
+			printk(KERN_CONT "%s:%ldKB ", mem_cgroup_stat_names[i],
This printk isn't continuing any previous printk, so using KERN_CONT here
will require a short header to be printed first ("Memcg: "?) with
KERN_INFO before the iterations.


Yep...I think I lost it while rebasing... sorry for the stupid mistake.

+				K(mem_cgroup_read_stat(memcg, i)));
+		}
+
+		for (i = 0; i<  MEM_CGROUP_EVENTS_NSTATS; i++)
+			printk(KERN_CONT "%s:%lu ", mem_cgroup_events_names[i],
+				mem_cgroup_read_events(memcg, i));
+
+		for (i = 0; i<  NR_LRU_LISTS; i++)
+			printk(KERN_CONT "%s:%luKB ", mem_cgroup_lru_names[i],
+				K(mem_cgroup_nr_lru_pages(memcg, BIT(i))));
+	} else {
+
Spurious newline.

Eek, is there really no way to avoid this if-conditional and just use
for_each_mem_cgroup_tree() for everything and use

	mem_cgroup_iter_break(memcg, iter);
	break;

for !memcg->use_hierarchy?


Now I'm shamed at my bad brain of yesterday by sending this chunk out...
Yes, the if-part code above is obviously unwanted, and the for_each_mem_cgroup_tree
can handle hierarchy already.


+		for (i = 0; i<  MEM_CGROUP_STAT_NSTATS; i++) {
+			long long val = 0;
+
+			if (i == MEM_CGROUP_STAT_SWAP&&  !do_swap_account)
+				continue;
+			for_each_mem_cgroup_tree(mi, memcg)
+				val += mem_cgroup_read_stat(mi, i);
+			printk(KERN_CONT "%s:%lldKB ", mem_cgroup_stat_names[i], K(val));
+		}
+
+		for (i = 0; i<  MEM_CGROUP_EVENTS_NSTATS; i++) {
+			unsigned long long val = 0;
+
+			for_each_mem_cgroup_tree(mi, memcg)
+				val += mem_cgroup_read_events(mi, i);
+			printk(KERN_CONT "%s:%llu ",
+				mem_cgroup_events_names[i], val);
+		}
+
+		for (i = 0; i<  NR_LRU_LISTS; i++) {
+			unsigned long long val = 0;
+
+			for_each_mem_cgroup_tree(mi, memcg)
+				val += mem_cgroup_nr_lru_pages(mi, BIT(i));
+			printk(KERN_CONT "%s:%lluKB ", mem_cgroup_lru_names[i], K(val));
+		}
+	}
+	printk(KERN_CONT "\n");
+}
  /**
- * mem_cgroup_print_oom_info: Called from OOM with tasklist_lock held in read mode.
   * @memcg: The memory cgroup that went over limit
   * @p: Task that is going to be killed
   *
@@ -1569,6 +1628,8 @@ done:
  		res_counter_read_u64(&memcg->kmem, RES_USAGE)>>  10,
  		res_counter_read_u64(&memcg->kmem, RES_LIMIT)>>  10,
  		res_counter_read_u64(&memcg->kmem, RES_FAILCNT));
+
+	mem_cgroup_print_oom_stat(memcg);
I think this should be folded into mem_cgroup_print_oom_info(), I don't
see a need for a new function.

  }

  /*
@@ -5195,14 +5256,6 @@ static int memcg_numa_stat_show(struct cgroup *cont, struct cftype *cft,
  }
  #endif /* CONFIG_NUMA */

-static const char * const mem_cgroup_lru_names[] = {
-	"inactive_anon",
-	"active_anon",
-	"inactive_file",
-	"active_file",
-	"unevictable",
-};
-
  static inline void mem_cgroup_lru_names_not_uptodate(void)
  {
  	BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_lru_names) != NR_LRU_LISTS);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 7e9e911..4b8a6dd 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -421,8 +421,10 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
  	cpuset_print_task_mems_allowed(current);
  	task_unlock(current);
  	dump_stack();
-	mem_cgroup_print_oom_info(memcg, p);
-	show_mem(SHOW_MEM_FILTER_NODES);
+	if (memcg)
+		mem_cgroup_print_oom_info(memcg, p);
mem_cgroup_print_oom_info() already returns immediately for !memcg, so I'm
not sure why this change is made.


Here the if-else checking is aiming at printing distinct messages for memcg & non-memcg. IMHO, global state has little actual use for memcg-oom and why not we wipe off it? Though mem_cgroup_print_oom_info already checking for !memcg, the if-statement can avoid one function call and save the deep-enough oom call stack a little.

+	else
+		show_mem(SHOW_MEM_FILTER_NODES);
Well that's disappointing if memcg == root_mem_cgroup, we'd probably like
to know the global memory state to determine what the problem is.


I really wondering if there is any case that can pass root_mem_cgroup down here. It's called by global or memcg oom killer and the global oom will set memcg=NULL directly instead of root_mem_cgroup. Besides, root memcg will not go through charging and there is no chance to call mem_cgroup_out_of_memory for root cgroup tasks.



Thanks,
Sha


  	if (sysctl_oom_dump_tasks)
  		dump_tasks(memcg, nodemask);
  }
.


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