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From:   Abel Wu <wuyun.abel@bytedance.com>
To:     akpm@linux-foundation.org, lizefan.x@bytedance.com, tj@kernel.org,
        hannes@cmpxchg.org, corbet@lwn.net
Cc:     cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Abel Wu <wuyun.abel@bytedance.com>
Subject: [PATCH 1/3] mm/mempolicy: apply cpuset limits to tasks using default policy
Date:   Mon, 26 Apr 2021 14:59:44 +0800
Message-Id: <20210426065946.40491-2-wuyun.abel@bytedance.com>
In-Reply-To: <20210426065946.40491-1-wuyun.abel@bytedance.com>
References: <20210426065946.40491-1-wuyun.abel@bytedance.com>
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The nodemasks of non-default policies (pol->v) are calculated within
the restriction of task->mems_allowed, while default policies are not.
This may lead to improper results of mpol_misplaced(), since it can
return a target node outside of current->mems_allowed for tasks using
default policies. Although this is not a bug because migrating pages
to that out-of-cpuset node will fail eventually due to sanity checks
in page allocation, it still would be better to avoid such useless
efforts.

This patch also changes the behavior of autoNUMA a bit by showing
a tendency to move pages inside mems_allowed for tasks using default
policies, which is good for memory isolation.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
---
 mm/mempolicy.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d79fa299b70c..e0ae6997bbfb 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2516,7 +2516,10 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long
 
 	/* Migrate the page towards the node whose CPU is referencing it */
 	if (pol->flags & MPOL_F_MORON) {
-		polnid = thisnid;
+		if (node_isset(thisnid, cpuset_current_mems_allowed))
+			polnid = thisnid;
+		else
+			polnid = node_random(&cpuset_current_mems_allowed);
 
 		if (!should_numa_migrate_memory(current, page, curnid, thiscpu))
 			goto out;
-- 
2.31.1