oom: select task from tasklist for mempolicy ooms

The oom killer presently kills current whenever there is no more memory
free or reclaimable on its mempolicy's nodes.  There is no guarantee that
current is a memory-hogging task or that killing it will free any
substantial amount of memory, however.

In such situations, it is better to scan the tasklist for nodes that are
allowed to allocate on current's set of nodes and kill the task with the
highest badness() score.  This ensures that the most memory-hogging task,
or the one configured by the user with /proc/pid/oom_adj, is always
selected in such scenarios.

Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5bc0a96beb51..8a73708d59bb 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1712,6 +1712,50 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
 }
 #endif
 
+/*
+ * mempolicy_nodemask_intersects
+ *
+ * If tsk's mempolicy is "default" [NULL], return 'true' to indicate default
+ * policy.  Otherwise, check for intersection between mask and the policy
+ * nodemask for 'bind' or 'interleave' policy.  For 'perferred' or 'local'
+ * policy, always return true since it may allocate elsewhere on fallback.
+ *
+ * Takes task_lock(tsk) to prevent freeing of its mempolicy.
+ */
+bool mempolicy_nodemask_intersects(struct task_struct *tsk,
+                                        const nodemask_t *mask)
+{
+        struct mempolicy *mempolicy;
+        bool ret = true;
+
+        if (!mask)
+                return ret;
+        task_lock(tsk);
+        mempolicy = tsk->mempolicy;
+        if (!mempolicy)
+                goto out;
+
+        switch (mempolicy->mode) {
+        case MPOL_PREFERRED:
+                /*
+                 * MPOL_PREFERRED and MPOL_F_LOCAL are only preferred nodes to
+                 * allocate from, they may fallback to other nodes when oom.
+                 * Thus, it's possible for tsk to have allocated memory from
+                 * nodes in mask.
+                 */
+                break;
+        case MPOL_BIND:
+        case MPOL_INTERLEAVE:
+                ret = nodes_intersects(mempolicy->v.nodes, *mask);
+                break;
+        default:
+                BUG();
+        }
+out:
+        task_unlock(tsk);
+        return ret;
+}
+
 /* Allocate a page in interleaved policy.
    Own path because it needs to do special accounting. */
 static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,