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SubjectRe: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
On Fri 08-02-19 10:06:04, Oscar Salvador wrote:
> isolate_huge_page() expects we pass the head of hugetlb page to it:
>
> bool isolate_huge_page(...)
> {
> ...
> VM_BUG_ON_PAGE(!PageHead(page), page);
> ...
> }
>
> While I really cannot think of any situation where we end up with a
> non-head page between hands in do_migrate_range(), let us make sure
> the code is as sane as possible by explicitly passing the Head.
> Since we already got the pointer, it does not take us extra effort.
>
> Signed-off-by: Oscar Salvador <osalvador@suse.de>

Acked-by: Michal Hocko <mhocko@suse.com>

Btw.

> ---
> mm/memory_hotplug.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 656ff386ac15..d5f7afda67db 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1378,12 +1378,12 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>
> if (PageHuge(page)) {
> struct page *head = compound_head(page);
> - pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> if (compound_order(head) > PFN_SECTION_SHIFT) {
> ret = -EBUSY;
> break;
> }

Why are we doing this, btw?

> - isolate_huge_page(page, &source);
> + pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> + isolate_huge_page(head, &source);
> continue;
> } else if (PageTransHuge(page))
> pfn = page_to_pfn(compound_head(page))
> --
> 2.13.7

--
Michal Hocko
SUSE Labs

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