Re: [PATCH v2 1/8] mm/compaction: avoid missing last page block in section after skip offline sections

[Baolin Wang]

On 8/2/2023 5:37 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")

The changes look good to me.
But the commit id is not stable, since it is not merged into mm-stable 
branch yet. Not sure how to handle this patch, squash it into the 
original patch? Andrew, what do you prefer?

> Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> ---
>   mm/compaction.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index cd23da4d2a5b..a8cea916df9d 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;
> @@ -1668,8 +1673,7 @@ 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;
>   		}