linux-kernel - Re: [PATCH v2] mm: show total hugetlb memory consumption in /proc/meminfo

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Date:   Mon, 20 Nov 2017 16:51:10 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Roman Gushchin <guro@...com>
Cc:     <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        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>,
        David Rientjes <rientjes@...gle.com>, <kernel-team@...com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm: show total hugetlb memory consumption in
 /proc/meminfo

On Wed, 15 Nov 2017 23:14:09 +0000 Roman Gushchin <guro@...com> wrote:

> Currently we display some hugepage statistics (total, free, etc)
> in /proc/meminfo, but only for default hugepage size (e.g. 2Mb).
> 
> If hugepages of different sizes are used (like 2Mb and 1Gb on x86-64),
> /proc/meminfo output can be confusing, as non-default sized hugepages
> are not reflected at all, and there are no signs that they are
> existing and consuming system memory.
> 
> To solve this problem, let's display the total amount of memory,
> consumed by hugetlb pages of all sized (both free and used).
> Let's call it "Hugetlb", and display size in kB to match generic
> /proc/meminfo style.
> 
> For example, (1024 2Mb pages and 2 1Gb pages are pre-allocated):
>   $ cat /proc/meminfo
>   MemTotal:        8168984 kB
>   MemFree:         3789276 kB
>   <...>
>   CmaFree:               0 kB
>   HugePages_Total:    1024
>   HugePages_Free:     1024
>   HugePages_Rsvd:        0
>   HugePages_Surp:        0
>   Hugepagesize:       2048 kB
>   Hugetlb:         4194304 kB
>   DirectMap4k:       32632 kB
>   DirectMap2M:     4161536 kB
>   DirectMap1G:     6291456 kB
> 
> Also, this patch updates corresponding docs to reflect
> Hugetlb entry meaning and difference between Hugetlb and
> HugePages_Total * Hugepagesize.
> 
> ...
>
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2973,20 +2973,32 @@ 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 count = h->nr_huge_pages;
> +
> +		total += (PAGE_SIZE << huge_page_order(h)) * count;
> +
> +		if (h == &default_hstate)

I'm not understanding this test.  Are we assuming that default_hstate
always refers to the highest-index hstate?  If so why, and is that
valid?

> +			seq_printf(m,
> +				   "HugePages_Total:   %5lu\n"
> +				   "HugePages_Free:    %5lu\n"
> +				   "HugePages_Rsvd:    %5lu\n"
> +				   "HugePages_Surp:    %5lu\n"
> +				   "Hugepagesize:   %8lu kB\n",
> +				   count,
> +				   h->free_huge_pages,
> +				   h->resv_huge_pages,
> +				   h->surplus_huge_pages,
> +				   (PAGE_SIZE << huge_page_order(h)) / 1024);
> +	}
> +
> +	seq_printf(m, "Hugetlb:        %8lu kB\n", total / 1024);
>  }