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SubjectRe: [PATCH 09/14] mm: __first_valid_page skip over offline pages
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On 05/15/2017 10:58 AM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> __first_valid_page skips over invalid pfns in the range but it might
> still stumble over offline pages. At least start_isolate_page_range
> will mark those set_migratetype_isolate. This doesn't represent
> any immediate AFAICS because alloc_contig_range will fail to isolate
> those pages but it relies on not fully initialized page which will
> become a problem later when we stop associating offline pages to zones.
> Use pfn_to_online_page to handle this.
>
> This is more a preparatory patch than a fix.
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>

Iterating over single pages when the whole section is offline seems
rather wasteful, but it should be really rare, so whatever.

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> mm/page_isolation.c | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 5092e4ef00c8..3606104893e0 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -138,12 +138,18 @@ static inline struct page *
> __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> {
> int i;
> - for (i = 0; i < nr_pages; i++)
> - if (pfn_valid_within(pfn + i))
> - break;
> - if (unlikely(i == nr_pages))
> - return NULL;
> - return pfn_to_page(pfn + i);
> +
> + for (i = 0; i < nr_pages; i++) {
> + struct page *page;
> +
> + if (!pfn_valid_within(pfn + i))
> + continue;
> + page = pfn_to_online_page(pfn + i);
> + if (!page)
> + continue;
> + return page;
> + }
> + return NULL;
> }
>
> /*
> @@ -184,8 +190,12 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> undo:
> for (pfn = start_pfn;
> pfn < undo_pfn;
> - pfn += pageblock_nr_pages)
> - unset_migratetype_isolate(pfn_to_page(pfn), migratetype);
> + pfn += pageblock_nr_pages) {
> + struct page *page = pfn_to_online_page(pfn);
> + if (!page)
> + continue;
> + unset_migratetype_isolate(page, migratetype);
> + }
>
> return -EBUSY;
> }
>

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