linux-kernel - Re: [PATCH] mm: show total hugetlb memory consumption in /proc/meminfo

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Date:   Wed, 15 Nov 2017 14:46:00 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
cc:     Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>, kernel-team@...com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: show total hugetlb memory consumption in
 /proc/meminfo

On Wed, 15 Nov 2017, Michal Hocko wrote:

> > > >  	if (!hugepages_supported())
> > > >  		return;
> > > >  	seq_printf(m,
> > > > @@ -2987,6 +2989,11 @@ void hugetlb_report_meminfo(struct seq_file *m)
> > > >  			h->resv_huge_pages,
> > > >  			h->surplus_huge_pages,
> > > >  			1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
> > > > +
> > > > +	for_each_hstate(h)
> > > > +		total += (PAGE_SIZE << huge_page_order(h)) * h->nr_huge_pages;
> > > 
> > > Please keep the total calculation consistent with what we have there
> > > already.
> > > 
> > 
> > Yeah, and I'm not sure if your comment eludes to this being racy, but it 
> > would be better to store the default size for default_hstate during the 
> > iteration to total the size for all hstates.
> 
> I just meant to have the code consistent. I do not prefer one or other
> option.

It's always nice when HugePages_Total * Hugepagesize cannot become greater 
than Hugetlb.  Roman, could you factor something like this into your 
change accompanied with a documentation upodate as suggested by Dave?

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2975,20 +2975,33 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write,
 
 void hugetlb_report_meminfo(struct seq_file *m)
 {
-	struct hstate *h = &default_hstate;
+	struct hstate *h;
+	unsigned long total = 0;
+
 	if (!hugepages_supported())
 		return;
-	seq_printf(m,
-			"HugePages_Total:   %5lu\n"
-			"HugePages_Free:    %5lu\n"
-			"HugePages_Rsvd:    %5lu\n"
-			"HugePages_Surp:    %5lu\n"
-			"Hugepagesize:   %8lu kB\n",
-			h->nr_huge_pages,
-			h->free_huge_pages,
-			h->resv_huge_pages,
-			h->surplus_huge_pages,
-			1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
+
+	for_each_hstate(h) {
+		unsigned long nr_huge_pages = h->nr_huge_pages;
+
+		total += nr_huge_pages <<
+			 (huge_page_order(h) + PAGE_SHIFT - 10);
+
+		if (h == &default_hstate) {
+			seq_printf(m,
+				"HugePages_Total:   %5lu\n"
+				"HugePages_Free:    %5lu\n"
+				"HugePages_Rsvd:    %5lu\n"
+				"HugePages_Surp:    %5lu\n"
+				"Hugepagesize:   %8lu kB\n",
+				nr_huge_pages,
+				h->free_huge_pages,
+				h->resv_huge_pages,
+				h->surplus_huge_pages,
+				1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
+		}
+	}
+	seq_printf(m, "Hugetlb:            %5lu kB\n", total);
 }
 
 int hugetlb_report_node_meminfo(int nid, char *buf)