oom: move oom_adj value from task_struct to mm_struct
The per-task oom_adj value is a characteristic of its mm more than the
task itself since it's not possible to oom kill any thread that shares the
mm. If a task were to be killed while attached to an mm that could not be
freed because another thread were set to OOM_DISABLE, it would have
needlessly been terminated since there is no potential for future memory
freeing.
This patch moves oomkilladj (now more appropriately named oom_adj) from
struct task_struct to struct mm_struct. This requires task_lock() on a
task to check its oom_adj value to protect against exec, but it's already
necessary to take the lock when dereferencing the mm to find the total VM
size for the badness heuristic.
This fixes a livelock if the oom killer chooses a task and another thread
sharing the same memory has an oom_adj value of OOM_DISABLE. This occurs
because oom_kill_task() repeatedly returns 1 and refuses to kill the
chosen task while select_bad_process() will repeatedly choose the same
task during the next retry.
Taking task_lock() in select_bad_process() to check for OOM_DISABLE and in
oom_kill_task() to check for threads sharing the same memory will be
removed in the next patch in this series where it will no longer be
necessary.
Writing to /proc/pid/oom_adj for a kthread will now return -EINVAL since
these threads are immune from oom killing already. They simply report an
oom_adj value of OOM_DISABLE.
Cc: Nick Piggin <npiggin@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a7b2460..b609135 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -58,6 +58,7 @@
unsigned long points, cpu_time, run_time;
struct mm_struct *mm;
struct task_struct *child;
+ int oom_adj;
task_lock(p);
mm = p->mm;
@@ -65,6 +66,7 @@
task_unlock(p);
return 0;
}
+ oom_adj = mm->oom_adj;
/*
* The memory size of the process is the basis for the badness.
@@ -148,15 +150,15 @@
points /= 8;
/*
- * Adjust the score by oomkilladj.
+ * Adjust the score by oom_adj.
*/
- if (p->oomkilladj) {
- if (p->oomkilladj > 0) {
+ if (oom_adj) {
+ if (oom_adj > 0) {
if (!points)
points = 1;
- points <<= p->oomkilladj;
+ points <<= oom_adj;
} else
- points >>= -(p->oomkilladj);
+ points >>= -(oom_adj);
}
#ifdef DEBUG
@@ -251,8 +253,12 @@
*ppoints = ULONG_MAX;
}
- if (p->oomkilladj == OOM_DISABLE)
+ task_lock(p);
+ if (p->mm && p->mm->oom_adj == OOM_DISABLE) {
+ task_unlock(p);
continue;
+ }
+ task_unlock(p);
points = badness(p, uptime.tv_sec);
if (points > *ppoints || !chosen) {
@@ -304,8 +310,7 @@
}
printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d %3d %s\n",
p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
- get_mm_rss(mm), (int)task_cpu(p), p->oomkilladj,
- p->comm);
+ get_mm_rss(mm), (int)task_cpu(p), mm->oom_adj, p->comm);
task_unlock(p);
} while_each_thread(g, p);
}
@@ -367,8 +372,12 @@
* Don't kill the process if any threads are set to OOM_DISABLE
*/
do_each_thread(g, q) {
- if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
+ task_lock(q);
+ if (q->mm == mm && q->mm && q->mm->oom_adj == OOM_DISABLE) {
+ task_unlock(q);
return 1;
+ }
+ task_unlock(q);
} while_each_thread(g, q);
__oom_kill_task(p, 1);
@@ -393,10 +402,11 @@
struct task_struct *c;
if (printk_ratelimit()) {
- printk(KERN_WARNING "%s invoked oom-killer: "
- "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
- current->comm, gfp_mask, order, current->oomkilladj);
task_lock(current);
+ printk(KERN_WARNING "%s invoked oom-killer: "
+ "gfp_mask=0x%x, order=%d, oom_adj=%d\n",
+ current->comm, gfp_mask, order,
+ current->mm ? current->mm->oom_adj : OOM_DISABLE);
cpuset_print_task_mems_allowed(current);
task_unlock(current);
dump_stack();