Fix card marking issue #64748
Fix card marking issue #64748
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The problem is that when we reach the end of a region during card marking, we clear the cards between card and card_of (end). If card_of (end) is equal to card, we end up clearing nothing at all. A similar problem occurs when cards happen to be set between end and the end of the reserved memory of the region - these cards would never be cleared. Both issues don't affect correctness, but they do affect performance for regions with very few cross generation pointers.
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Tagging subscribers to this area: @dotnet/gc Issue DetailsFix issue where we didn't clear cards at the ends of regions. The problem is that when we reach the end of a region during card marking, we clear the cards between card and card_of (end). If card_of (end) is equal to card, we end up clearing nothing at all. A similar problem occurs when cards happen to be set between end and the end of the reserved memory of the region - these cards would never be cleared. Both issues don't affect correctness, but they do affect performance for regions with very few cross generation pointers. The fix is very simple - end_card already contains the first clear card after the current run of cards, so [card, end_card[ is exactly the correct range to pass to clear_cards.
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I found that I didn't get the segment case correct - there we may clear too many cards at the end of gen 2 if gen 1 follows in the same segment. Fix is to go back to the equivalent of the old code. |
ghost
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Fix issue where we didn't clear cards at the ends of regions.
The problem is that when we reach the end of a region during card marking, we clear the cards between card and card_of (end). If card_of (end) is equal to card, we end up clearing nothing at all.
A similar problem occurs when cards happen to be set between end and the end of the reserved memory of the region - these cards would never be cleared.
Both issues don't affect correctness, but they do affect performance for regions with very few cross generation pointers.
The fix is very simple - end_card already contains the first clear card after the current run of cards, so [card, end_card[ is exactly the correct range to pass to clear_cards.