linux-kernel - [PATCH 26/63] sched: Check current->mm before allocating NUMA faults

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Message-Id: <1380288468-5551-27-git-send-email-mgorman@suse.de>
Date:	Fri, 27 Sep 2013 14:27:11 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 26/63] sched: Check current->mm before allocating NUMA faults

task_numa_placement checks current->mm but after buffers for faults
have already been uselessly allocated. Move the check earlier.

[peterz@...radead.org: Identified the problem]
Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 kernel/sched/fair.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 96f6f08..7b7bc48 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -930,8 +930,6 @@ static void task_numa_placement(struct task_struct *p)
 	int seq, nid, max_nid = -1;
 	unsigned long max_faults = 0;
 
-	if (!p->mm)	/* for example, ksmd faulting in a user's mm */
-		return;
 	seq = ACCESS_ONCE(p->mm->numa_scan_seq);
 	if (p->numa_scan_seq == seq)
 		return;
@@ -998,6 +996,10 @@ void task_numa_fault(int last_nid, int node, int pages, bool migrated)
 	if (!numabalancing_enabled)
 		return;
 
+	/* for example, ksmd faulting in a user's mm */
+	if (!p->mm)
+		return;
+
 	/* For now, do not attempt to detect private/shared accesses */
 	priv = 1;
 
-- 
1.8.1.4

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