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SubjectRe: [PATCH v2] mm: show total hugetlb memory consumption in /proc/meminfo
On Wed, 15 Nov 2017 23:14:09 +0000 Roman Gushchin <guro@fb.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);
> }

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