Messages in this thread | | | Date | Tue, 1 Aug 2023 11:53:45 +0800 | Subject | Re: [PATCH 1/8] mm/compaction: avoid missing last page block in section after skip offline sections | From | Baolin Wang <> |
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On 8/1/2023 10:36 AM, Kemeng Shi wrote: > > > on 8/1/2023 10:18 AM, Kemeng Shi wrote: >> >> >> on 7/31/2023 8:01 PM, Baolin Wang wrote: >>> >>> >>> On 7/29/2023 1:10 AM, 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 >>>> @@ -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); >>> >>> This is incorrect, you returned the start pfn of this section. >>> >>>> } >>>> 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); >>> >>> 'block_start_pfn' should be pageblock aligned. If the 'next_pfn' is not pageblock-aligned (though this is not the common case), we should skip it. >>> >>> But if the 'next_pfn' is pageblock-aligned, yes, the commit f63224525309 still ignores the last pageblock, which is not right. So I think it should be: >>> block_start_pfn = pageblock_aligned(next_pfn) ? : pageblock_start_pfn(next_pfn); >>> block_start_pfn = max(block_start_pfn, low_pfn); >>> >> Hi Baolin, thanks for reply! As skip_offline_sections_reverse is based >> on skip_offline_sections. I make the assumption that section is pageblock >> aligned based on that we use section start from skip_offline_sections as >> block_start_fpn without align check. >> If section size is not pageblock aligned in real world, the pageblock aligned >> check should be added to skip_offline_sections and skip_offline_sections_reverse. >> If no one is against this, I will fix this in next version. THanks! >> > More information of aligment of section. For powerpc arch, we have SECTION_SIZE_BITS > with 24 while PAGE_SHIFT could be configured to 18. > Pageblock order is (18 + MAX_ORDER) which coule be 28 and is > SECTION_SZIE_BITS 24,
The maximum pageblock order is MAX_ORDER. But after thinking more, I think return the start pfn or end pfn of a section is okay, and it should be aligned to a pageblock order IIUC.
So I think your change is good: + block_start_pfn = max(next_pfn, low_pfn);
But in skip_offline_sections_reverse(), we should still return the last pfn of the online section.
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