[patch -mm 5/6] oom: sacrifice child with highest badness score for parent fix

[David Rientjes <rientjes@google.com>]

Elaborate on the comment in oom_kill_process() so it's clear why a
killable child with a different mm is sacrificied for its parent.

At the same time, rename auto variable `c' to "child" and move "cpoints"
inside the list_for_each_entry() loop with a more descriptive name as
akpm suggests.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   25 +++++++++++++++----------
 1 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -440,7 +440,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 			    const char *message)
 {
 	struct task_struct *victim = p;
-	struct task_struct *c;
+	struct task_struct *child;
 	struct task_struct *t = p;
 	unsigned long victim_points = 0;
 	struct timespec uptime;
@@ -462,22 +462,27 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 		message, task_pid_nr(p), p->comm, points);
 	task_unlock(p);
 
-	/* Try to sacrifice the worst child first */
+	/*
+	 * If any of p's children has a different mm and is eligible for kill,
+	 * the one with the highest badness() score is sacrificed for its
+	 * parent.  This attempts to lose the minimal amount of work done while
+	 * still freeing memory.
+	 */
 	do_posix_clock_monotonic_gettime(&uptime);
 	do {
-		unsigned long cpoints;
+		list_for_each_entry(child, &t->children, sibling) {
+			unsigned long child_points;
 
-		list_for_each_entry(c, &t->children, sibling) {
-			if (c->mm == p->mm)
+			if (child->mm == p->mm)
 				continue;
-			if (mem && !task_in_mem_cgroup(c, mem))
+			if (mem && !task_in_mem_cgroup(child, mem))
 				continue;
 
 			/* badness() returns 0 if the thread is unkillable */
-			cpoints = badness(c, uptime.tv_sec);
-			if (cpoints > victim_points) {
-				victim = c;
-				victim_points = cpoints;
+			child_points = badness(child, uptime.tv_sec);
+			if (child_points > victim_points) {
+				victim = child;
+				victim_points = child_points;
 			}
 		}
 	} while_each_thread(p, t);

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