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

David Rientjes
2017-11-14T22:28:18Z

On Tue, 14 Nov 2017, Michal Hocko 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
> >
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Mike Kravetz <mike.kravetz@oracle.com>
> > Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> > Cc: Andrea Arcangeli <aarcange@redhat.com>
> > Cc: Dave Hansen <dave.hansen@intel.com>
> > Cc: kernel-team@fb.com
> > Cc: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org

Acked-by: David Rientjes <rientjes@google.com>

> /proc/meminfo is paved with mistakes throughout the history. It pretends
> to give a good picture of the memory usage, yet we have many pointless
> entries while large consumers are not reflected at all in many case.
>
> Hugetlb data with that great details shouldn't have been exported in the
> first place when they reflect only one specific hugepage size. I would
> argue that if somebody went down to configure non-default hugetlb page
> sizes then checking for the sysfs stats would be an immediate place to
> look at. Anyway I can see that the cumulative information might be
> helpful for those who do not own the machine but merely debug an issue
> which is the primary usacase for the file.
>

I agree in principle, but I think it's inevitable on projects that span
decades and accumulate features that evolve over time.

> > ---
> > mm/hugetlb.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 4b3bbd2980bb..1a65f8482282 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -2974,6 +2974,8 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write,
> > void hugetlb_report_meminfo(struct seq_file *m)
> > {
> > struct hstate *h = &default_hstate;
> > + unsigned long total = 0;
> > +
> > 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.

> > +
> > + seq_printf(m, "Hugetlb: %8lu kB\n", total / 1024);
> > }
> >
> > int hugetlb_report_node_meminfo(int nid, char *buf)