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SubjectRe: [PATCH v2] mm: show total hugetlb memory consumption in /proc/meminfo
On Mon, Nov 20, 2017 at 04:51:10PM -0800, Andrew Morton wrote:
> 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?

As Mike and Michal pointed, default_hstate is defined as
#define default_hstate (hstates[default_hstate_idx]),
where default_hstate_idx can be altered by a boot argument.

We're iterating over all states to calculate total and also
print some additional info for the default size. Having a single
loop guarantees consistency of these numbers.

Thanks!

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