linux-kernel - [RFC Patch v2 1/4] mm/mempolicy: skip nodemask intersect check for 'interleave' when oom

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Date:   Thu, 20 May 2021 16:30:01 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>, ying.huang@...el.com,
        Feng Tang <feng.tang@...el.com>
Subject: [RFC Patch v2 1/4] mm/mempolicy: skip nodemask intersect check for 'interleave' when oom

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

MPOL_INTERLEAVE has set a nodemask, which is not a forced requirement,
but just a hint for chosing a node to allocate memory from, and the
task may have memory allocated on other nodes than this nodemask. So
skip the check.

Suggested-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Feng Tang <feng.tang@...el.com>
---
 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