Re: [PATCH v3 1/8] mm/compaction: avoid missing last page block in section after skip offline sections

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 8/4/2023 7:04 PM, 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")

Again, the Fixes tag is not stable. Please consider squashing it into 
the original commit or hold this patch until the original patch is 
merged into mm-stable branch.

Andrew,
What do you prefer? Thanks.

> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> 
> ---
>   mm/compaction.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 006fc35bffa1..a21b834c5898 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -250,6 +250,11 @@ static unsigned long skip_offline_sections(unsigned long start_pfn)
>   	return 0;
>   }
>   
> +/*
> + * If the PFN falls into an offline section, return the end PFN of the
> + * next online section in reverse. If the PFN falls into an online section
> + * or if there is no next online section in reverse, return 0.
> + */
>   static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
>   {
>   	unsigned long start_nr = pfn_to_section_nr(start_pfn);
> @@ -259,7 +264,7 @@ 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) + PAGES_PER_SECTION;
>   	}
>   
>   	return 0;
> @@ -1690,8 +1695,7 @@ 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);
>   
>   			continue;
>   		}