Messages in this thread | | | Date | Tue, 15 Aug 2023 18:07:58 +0800 | Subject | Re: [PATCH 4/9] mm/compaction: simplify pfn iteration in isolate_freepages_range | From | Baolin Wang <> |
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On 8/15/2023 5:32 PM, Kemeng Shi wrote: > > > on 8/15/2023 4:38 PM, Baolin Wang wrote: >> >> >> On 8/5/2023 7:07 PM, Kemeng Shi wrote: >>> We call isolate_freepages_block in strict mode, continuous pages in >>> pageblock will be isolated if isolate_freepages_block successed. >>> Then pfn + isolated will point to start of next pageblock to scan >>> no matter how many pageblocks are isolated in isolate_freepages_block. >>> Use pfn + isolated as start of next pageblock to scan to simplify the >>> iteration. >> >> IIUC, the isolate_freepages_block() can isolate high-order free pages, which means the pfn + isolated can be larger than the block_end_pfn. So in your patch, the 'block_start_pfn' and 'block_end_pfn' can be in different pageblocks, that will break pageblock_pfn_to_page(). >> > In for update statement, we always update block_start_pfn to pfn and
I mean, you changed to: 1) pfn += isolated; 2) block_start_pfn = pfn; 3) block_end_pfn = pfn + pageblock_nr_pages;
But in 1) pfn + isolated can go outside of the currnet pageblock if isolating a high-order page, for example, located in the middle of the next pageblock. So that the block_start_pfn can point to the middle of the next pageblock, not the start position. Meanwhile after 3), the block_end_pfn can point another pageblock. Or I missed something else?
> update block_end_pfn to pfn + pageblock_nr_pages. So they should point > to the same pageblock. I guess you missed the change to update of > block_end_pfn. :) >>> >>> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com> >>> --- >>> mm/compaction.c | 14 ++------------ >>> 1 file changed, 2 insertions(+), 12 deletions(-) >>> >>> diff --git a/mm/compaction.c b/mm/compaction.c >>> index 684f6e6cd8bc..8d7d38073d30 100644 >>> --- a/mm/compaction.c >>> +++ b/mm/compaction.c >>> @@ -733,21 +733,11 @@ isolate_freepages_range(struct compact_control *cc, >>> block_end_pfn = pageblock_end_pfn(pfn); >>> for (; pfn < end_pfn; pfn += isolated, >>> - block_start_pfn = block_end_pfn, >>> - block_end_pfn += pageblock_nr_pages) { >>> + block_start_pfn = pfn, >>> + block_end_pfn = pfn + pageblock_nr_pages) { >>> /* Protect pfn from changing by isolate_freepages_block */ >>> unsigned long isolate_start_pfn = pfn; >>> - /* >>> - * pfn could pass the block_end_pfn if isolated freepage >>> - * is more than pageblock order. In this case, we adjust >>> - * scanning range to right one. >>> - */ >>> - if (pfn >= block_end_pfn) { >>> - block_start_pfn = pageblock_start_pfn(pfn); >>> - block_end_pfn = pageblock_end_pfn(pfn); >>> - } >>> - >>> block_end_pfn = min(block_end_pfn, end_pfn); >>> if (!pageblock_pfn_to_page(block_start_pfn, >>
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