on 7/28/2023 6:41 PM, David Hildenbrand wrote:
> 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@xxxxxxxxxxxxxxx>
>> ---
>> 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)?
>
Hi David, thanks for the review. Sure, I will add comment to skip_offline_sections_reverse.
--
Best wishes
Kemeng Shi
>> @@ -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 :)
>
