linux-kernel - Re: [PATCH] mm: mempolicy: fix policy_nodemask() for MPOL_PREFERRED

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Date:   Wed, 3 Aug 2022 13:28:59 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "bwidawsk@...nel.org" <bwidawsk@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH] mm: mempolicy: fix policy_nodemask() for
 MPOL_PREFERRED_MANY case

On Thu 04-08-22 01:14:32, Feng Tang wrote:
[...]
> Ok, I change it as below:

Wouldn't it be better to make this allowed_mems_nr specific to be
explicit about the intention?

Not that I feel strongly about that.

> ---
>  mm/hugetlb.c | 28 +++++++++++++++++++++++-----
>  1 file changed, 23 insertions(+), 5 deletions(-)

Not even compile tested
 include/linux/mempolicy.h | 12 ------------
 mm/hugetlb.c              | 24 ++++++++++++++++++++----
 2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 668389b4b53d..e38b0ef20b8b 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -151,13 +151,6 @@ extern bool mempolicy_in_oom_domain(struct task_struct *tsk,
 				const nodemask_t *mask);
 extern nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *policy);
 
-static inline nodemask_t *policy_nodemask_current(gfp_t gfp)
-{
-	struct mempolicy *mpol = get_task_policy(current);
-
-	return policy_nodemask(gfp, mpol);
-}
-
 extern unsigned int mempolicy_slab_node(void);
 
 extern enum zone_type policy_zone;
@@ -294,11 +287,6 @@ static inline void mpol_put_task_policy(struct task_struct *task)
 {
 }
 
-static inline nodemask_t *policy_nodemask_current(gfp_t gfp)
-{
-	return NULL;
-}
-
 static inline bool mpol_is_preferred_many(struct mempolicy *pol)
 {
 	return  false;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a18c071c294e..6cacbc9b15a1 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4330,18 +4330,34 @@ static int __init default_hugepagesz_setup(char *s)
 }
 __setup("default_hugepagesz=", default_hugepagesz_setup);
 
+struct mempolicy *policy_mbind_nodemask(gfp_t gfp)
+{
+#ifdef CONFIG_MEMPOLICY
+	struct mempolicy *mpol = get_task_policy(current);
+
+	/*
+	 * only enforce MBIND which overlaps with cpuset policy (from policy_nodemask)
+	 * specifically for hugetlb case
+	 */
+	if (mpol->mode == MPOL_BIND &&
+		(apply_policy_zone(mpol, gfp_zone(gfp)) &&
+		 cpuset_nodemask_valid_mems_allowed(&policy->nodes))
+		return &mpol->nodes;
+#endif
+	return NULL;
+}
+
 static unsigned int allowed_mems_nr(struct hstate *h)
 {
 	int node;
 	unsigned int nr = 0;
-	nodemask_t *mpol_allowed;
+	nodemask_t *mbind_nodemask;
 	unsigned int *array = h->free_huge_pages_node;
 	gfp_t gfp_mask = htlb_alloc_mask(h);
 
-	mpol_allowed = policy_nodemask_current(gfp_mask);
-
+	mbind_nodemask = policy_mbind_nodemask(gfp_mask);
 	for_each_node_mask(node, cpuset_current_mems_allowed) {
-		if (!mpol_allowed || node_isset(node, *mpol_allowed))
+		if (!mbind_nodemask || node_isset(node, *mbind_nodemask))
 			nr += array[node];
 	}
 
-- 
Michal Hocko
SUSE Labs