Messages in this thread | | | Subject | Re: [PATCH v2] mm: show total hugetlb memory consumption in /proc/meminfo | From | Mike Kravetz <> | Date | Tue, 21 Nov 2017 16:27:38 -0800 |
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On 11/21/2017 11:59 AM, Roman Gushchin wrote: > On Tue, Nov 21, 2017 at 11:19:07AM -0800, Andrew Morton wrote: >> >> Why not >> >> 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) >> total += (PAGE_SIZE << huge_page_order(h)) * h->nr_huge_pages; >> seq_printf(m, "Hugetlb: %8lu kB\n", total / 1024); >> >> ? > > The idea was that the local variable guarantees the consistency > between Hugetlb and HugePages_Total numbers. Otherwise we have > to take hugetlb_lock.
Most important it prevents HugePages_Total from being larger than Hugetlb.
> What we can do, is to rename "count" into "nr_huge_pages", like: > > for_each_hstate(h) { > unsigned long nr_huge_pages = h->nr_huge_pages; > > total += (PAGE_SIZE << huge_page_order(h)) * nr_huge_pages; > > 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, > (PAGE_SIZE << huge_page_order(h)) / 1024); > } > > seq_printf(m, "Hugetlb: %8lu kB\n", total / 1024); > > But maybe taking a lock is not a bad idea, because it will also > guarantee consistency between other numbers (like HugePages_Free) as well, > which is not true right now.
You are correct in that there is no consistency guarantee for the numbers with the default huge page size today. However, I am not really a fan of taking the lock for that guarantee. IMO, the above code is fine.
This discussion reminds me that ideally there should be a per-hstate lock. My guess is that the global lock is a carry over from the days when only a single huge page size was supported. In practice, I don't think this is much of an issue as people typically only use a single huge page size. But, if anyone thinks is/may be an issue I am happy to make the changes.
-- Mike Kravetz
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