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## Taking Off the Gloves with Reference Counting ImmixTaking Off the Gloves with Reference Counting Immix, by Rifat Shahriyar, Stephen M. Blackburn, and Kathryn S. McKinley:
A new reference counting GC based on the Immix heap layout, which purports to close the remaining performance gap with tracing collectors. It builds on last year's work, Down for the count? Getting reference counting back in the ring, which describes various optimizations to raw reference counting that make it competitive with basic tracing. There's a remaining 10% performance gap with generational tracing that RCImmix closes by using the Immix heap layout with bump pointer allocation (as opposed to free lists typically used in RC). The improved cache locality of allocation makes RCImmix even faster than the generational tracing Immix collector. However, the bump pointer allocation reduces the incrementality of reference counting and would impact latency. One glaring omission of this paper is the absence of latency/pause time measurements, which is typical of reference counting papers since ref counting is inherently incremental. Since RCImmix trades off some incrementality for throughput by using bump pointer allocation and copy collection, I'm curious how this impacts the pause times. Reference counting has been discussed a few times here before, and some papers on past ref-counting GC's have been posted in comments, but this seems to be the first top-level post on competitive reference counting GC. |
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