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A comment on Chris Lattner on garbage collection vs. Automatic Reference Counting (2017). Parent comment

Re:Chris Lattner on garbage collection vs. Automatic Referen... by cmrdporcupine on Saturday April 23, 2022 @11:09PM (#31140958)
There are RC systems where the counts are held external to the objects, which can be a bit more cache friendly.
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Re:Chris Lattner on garbage collection vs. Automatic Referen... by Kranar on Sunday April 24, 2022 @01:45AM (#31141581)
You want the opposite behavior in order to be cache friendly, an RC system where the counts are stored next to the object.
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Re:Chris Lattner on garbage collection vs. Automatic Referen... by cmrdporcupine on Sunday April 24, 2022 @08:56AM (#31143502)
Not necessarily. The issue is that releasing a reference at the top of a tree of objects has the potential to walk a large graph of objects (doing downcounts at each) that are not in cache, causing some thrash.

In an ideal world and in a program running with a not-huge # of objects you could keep the entire basket of reference counts in L1 cache, separate from the objects. Then decrements would be potentially cheap. A bit utopian though.

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