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SubjectRe: [PATCH] mm/hugetlb: allow gigantic page allocation to migrate away smaller huge page
On Mon, Jun 24, 2019 at 12:21:08PM +0800, Pingfan Liu wrote:
> The current pfn_range_valid_gigantic() rejects the pud huge page allocation
> if there is a pmd huge page inside the candidate range.
>
> But pud huge resource is more rare, which should align on 1GB on x86. It is
> worth to allow migrating away pmd huge page to make room for a pud huge
> page.
>
> The same logic is applied to pgd and pud huge pages.

I'm sorry but I don't quite understand why we should do this. Is this a bug or
an optimization? It sounds like an optimization.

>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-kernel@vger.kernel.org
> ---
> mm/hugetlb.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ac843d3..02d1978 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1081,7 +1081,11 @@ static bool pfn_range_valid_gigantic(struct zone *z,
> unsigned long start_pfn, unsigned long nr_pages)
> {
> unsigned long i, end_pfn = start_pfn + nr_pages;
> - struct page *page;
> + struct page *page = pfn_to_page(start_pfn);
> +
> + if (PageHuge(page))
> + if (compound_order(compound_head(page)) >= nr_pages)

I don't think you want compound_order() here.

Ira

> + return false;
>
> for (i = start_pfn; i < end_pfn; i++) {
> if (!pfn_valid(i))
> @@ -1098,8 +1102,6 @@ static bool pfn_range_valid_gigantic(struct zone *z,
> if (page_count(page) > 0)
> return false;
>
> - if (PageHuge(page))
> - return false;
> }
>
> return true;
> --
> 2.7.5
>

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