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SubjectRe: [PATCH 1/8] mm/compaction: avoid missing last page block in section after skip offline sections
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On 28.07.23 19:10, Kemeng Shi wrote:
> skip_offline_sections_reverse will return the last pfn in found online
> section. Then we set block_start_pfn to start of page block which
> contains the last pfn in section. Then we continue, move one page
> block forward and ignore the last page block in the online section.
> Make block_start_pfn point to first page block after online section to fix
> this:
> 1. make skip_offline_sections_reverse return end pfn of online section,
> i.e. pfn of page block after online section.
> 2. assign block_start_pfn with next_pfn.
>
> Fixes: f63224525309 ("mm: compaction: skip the memory hole rapidly when isolating free pages")
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> ---
> mm/compaction.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 9b7a0a69e19f..ce7841363b12 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c

Can we add a short comment which kind of PFN we return (first pfn of
first offline section after an online section)?

> @@ -259,7 +259,7 @@ static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
>
> while (start_nr-- > 0) {
> if (online_section_nr(start_nr))
> - return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION - 1;
> + return section_nr_to_pfn(start_nr + 1);
> }
>
> return 0;
> @@ -1670,8 +1670,7 @@ static void isolate_freepages(struct compact_control *cc)
>
> next_pfn = skip_offline_sections_reverse(block_start_pfn);
> if (next_pfn)
> - block_start_pfn = max(pageblock_start_pfn(next_pfn),
> - low_pfn);
> + block_start_pfn = max(next_pfn, low_pfn);


So block_start_pfn() will now point at the first PFN of the offline section.

Confusing stuff, but I get the idea and I think it makes sense to me :)

--
Cheers,

David / dhildenb

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