[PATCH] mm/oom_kill: set oc->constraint in constrained_alloc()

[Yafang Shao <laoar.shao@gmail.com>]

In dump_oom_summary() oc->constraint is used to show
oom_constraint_text, but it hasn't been set before.
So the value of it is always the default value 0.
We should set it in constrained_alloc().

Bellow is the output when memcg oom occurs,

before this patch:
[  133.078102] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),
cpuset=/,mems_allowed=0,oom_memcg=/foo,task_memcg=/foo,task=bash,pid=7997,uid=0

after this patch:
[  952.977946] oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),
cpuset=/,mems_allowed=0,oom_memcg=/foo,task_memcg=/foo,task=bash,pid=13681,uid=0

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 mm/oom_kill.c | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5a58778..075e5cf 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -261,29 +261,37 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 	struct zone *zone;
 	struct zoneref *z;
 	enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
+	enum oom_constraint constraint;
 	bool cpuset_limited = false;
 	int nid;
 
 	if (is_memcg_oom(oc)) {
 		oc->totalpages = mem_cgroup_get_max(oc->memcg) ?: 1;
-		return CONSTRAINT_MEMCG;
+		constraint = CONSTRAINT_MEMCG;
+		goto out;
 	}
 
 	/* Default to all available memory */
 	oc->totalpages = totalram_pages() + total_swap_pages;
 
-	if (!IS_ENABLED(CONFIG_NUMA))
-		return CONSTRAINT_NONE;
+	if (!IS_ENABLED(CONFIG_NUMA)) {
+		constraint = CONSTRAINT_NONE;
+		goto out;
+	}
 
-	if (!oc->zonelist)
-		return CONSTRAINT_NONE;
+	if (!oc->zonelist) {
+		constraint = CONSTRAINT_NONE;
+		goto out;
+	}
 	/*
 	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
 	 * to kill current.We have to random task kill in this case.
 	 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
 	 */
-	if (oc->gfp_mask & __GFP_THISNODE)
-		return CONSTRAINT_NONE;
+	if (oc->gfp_mask & __GFP_THISNODE) {
+		constraint = CONSTRAINT_NONE;
+		goto out;
+	}
 
 	/*
 	 * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
@@ -295,7 +303,8 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 		oc->totalpages = total_swap_pages;
 		for_each_node_mask(nid, *oc->nodemask)
 			oc->totalpages += node_spanned_pages(nid);
-		return CONSTRAINT_MEMORY_POLICY;
+		constraint = CONSTRAINT_MEMORY_POLICY;
+		goto out;
 	}
 
 	/* Check this allocation failure is caused by cpuset's wall function */
@@ -308,9 +317,15 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 		oc->totalpages = total_swap_pages;
 		for_each_node_mask(nid, cpuset_current_mems_allowed)
 			oc->totalpages += node_spanned_pages(nid);
-		return CONSTRAINT_CPUSET;
+		constraint = CONSTRAINT_CPUSET;
+		goto out;
 	}
-	return CONSTRAINT_NONE;
+
+	constraint = CONSTRAINT_NONE;
+
+out:
+	oc->constraint = constraint;
+	return constraint;
 }
 
 static int oom_evaluate_task(struct task_struct *task, void *arg)
-- 
1.8.3.1