[PATCH v1 1/4] mm/mempolicy: skip nodemask intersect check for 'interleave' when oom

[Feng Tang]

mempolicy_nodemask_intersects() is used in oom case to check if a
task may have memory allocated on some memory nodes.

Currently, the nodes_intersects() is run for both 'bind' and 'interleave'
policies. But they are different regarding memory allocation, the nodemask
is a forced requirement for 'bind', while just a hint for 'interleave'.
Like in alloc_pages_vma():

	nmask = policy_nodemask(gfp, pol);
        preferred_nid = policy_node(gfp, pol, node);
        page = __alloc_pages(gfp, order, preferred_nid, nmask);

in plicy_nodemask(), only 'bind' policy may return its desired nodemask,
while others return NULL.  And this 'NULL' enables the 'interleave' policy
can get memory from other nodes than its nodemask.

So skip the nodemask intersect check for 'interleave' policy.

Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
---
 mm/mempolicy.c | 24 ++++--------------------
 1 file changed, 4 insertions(+), 20 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d79fa29..1964cca 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2098,7 +2098,7 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
  *
  * 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 'preferred' or 'local'
+ * nodemask for 'bind' policy.  For 'interleave', 'preferred' or 'local'
  * policy, always return true since it may allocate elsewhere on fallback.
  *
  * Takes task_lock(tsk) to prevent freeing of its mempolicy.
@@ -2111,29 +2111,13 @@ bool mempolicy_nodemask_intersects(struct task_struct *tsk,
 
 	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:
+	if (mempolicy && mempolicy->mode == MPOL_BIND)
 		ret = nodes_intersects(mempolicy->v.nodes, *mask);
-		break;
-	default:
-		BUG();
-	}
-out:
 	task_unlock(tsk);
+
 	return ret;
 }
 
-- 
2.7.4