Copilot commented on code in PR #13893:
URL: https://github.com/apache/trafficserver/pull/13893#discussion_r4366103236
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src/iocore/cache/RamCacheCLFUS.cc:
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@@ -243,6 +247,38 @@ RamCacheCLFUS::init(int64_t abytes, StripeSM *astripe)
}
}
+// Advance one epoch for every full decay interval that has elapsed, so idle
+// periods age popularity as much as busy ones. Called from both get() and
+// put() so that hit-only traffic still ages entries.
+void
+RamCacheCLFUS::_decay_epochs()
+{
+ ink_hrtime now = ink_get_hrtime();
+ ink_hrtime elapsed = now - this->_last_decay_time;
+
+ if (elapsed < decay_interval) {
+ return;
+ }
+ // 32 or more epochs clears every hit count, so the advance can be capped
+ // without changing the result while keeping _epoch differences in range.
+ int epochs = static_cast<int>(std::min<ink_hrtime>(elapsed /
decay_interval, 32));
+ this->_epoch += epochs;
+ this->_average_value = std::ldexp(this->_average_value, -epochs);
Review Comment:
The 32-epoch cap clears `uint32_t` hit counts, but stops `_average_value`
from aging by all elapsed intervals. After 40 idle intervals, an average of 8
becomes approximately 1.86e-9 instead of 7.28e-12, leaving the threshold above
its intended value. Keep the capped advance for entry epochs, decay the average
by the full interval count, and assert the expected value in the long-idle test.
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