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Date:   Wed, 22 Jul 2020 16:49:13 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org
Subject: Re: [PATCH 5/5] mm/hugetl.c: warn out if expected count of huge
 pages adjustment is not achieved
Message-ID: <20200722084913.GO32539@MiWiFi-R3L-srv>
References: <20200720062623.13135-1-bhe@redhat.com>
 <20200720062623.13135-6-bhe@redhat.com>
 <c5eb3692-2d05-d6dc-437d-21e51705560e@oracle.com>
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Hi Mike,

On 07/20/20 at 05:38pm, Mike Kravetz wrote:
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 467894d8332a..1dfb5d9e4e06 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -2661,7 +2661,7 @@ static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
> >  static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
> >  			      nodemask_t *nodes_allowed)
> >  {
> > -	unsigned long min_count, ret;
> > +	unsigned long min_count, ret, old_max;
> >  	NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);
> >  
> >  	/*
> > @@ -2723,6 +2723,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
> >  	 * pool might be one hugepage larger than it needs to be, but
> >  	 * within all the constraints specified by the sysctls.
> >  	 */
> > +	old_max = persistent_huge_pages(h);
> >  	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
> >  		if (!adjust_pool_surplus(h, nodes_allowed, -1))
> >  			break;
> > @@ -2779,6 +2780,16 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
> >  	}
> >  out:
> >  	h->max_huge_pages = persistent_huge_pages(h);
> > +	if (count != h->max_huge_pages) {
> > +		char buf[32];
> > +
> > +		string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
> > +		pr_warn("HugeTLB: %s %lu of page size %s failed. Only %s %lu hugepages.\n",
> > +			count > old_max ? "increasing" : "decreasing",
> > +			abs(count - old_max), buf,
> > +			count > old_max ? "increased" : "decreased",
> > +			abs(old_max - h->max_huge_pages));
> > +	}
> >  	spin_unlock(&hugetlb_lock);
> 
> I would prefer if we drop the lock before logging the message.  That would
> involve grabbing the value of h->max_huge_pages before dropping the lock.

Do you think the below change is OK to you to move the message logging
after lock dropping? If yes, I will repost with updated patches.

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6a9b7556ce5b..b5aa32a13569 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2661,7 +2661,7 @@ static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
 static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 			      nodemask_t *nodes_allowed)
 {
-	unsigned long min_count, ret, old_max;
+	unsigned long min_count, ret, old_max, new_max;
 	NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);
 
 	/*
@@ -2780,7 +2780,10 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	}
 out:
 	h->max_huge_pages = persistent_huge_pages(h);
-	if (count != h->max_huge_pages) {
+	new_max = h->max_huge_pages;
+	spin_unlock(&hugetlb_lock);
+
+	if (count != new_max) {
 		char buf[32];
 
 		string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
@@ -2788,9 +2791,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 			count > old_max ? "increasing" : "decreasing",
 			abs(count - old_max), buf,
 			count > old_max ? "increased" : "decreased",
-			abs(old_max - h->max_huge_pages));
+			abs(old_max - new_max));
 	}
-	spin_unlock(&hugetlb_lock);
 
 	NODEMASK_FREE(node_alloc_noretry);