MB-40531: Make replica eviction ignore age threshold
MB-40531: Make replica eviction ignore age threshold

Normally items above a configured MFU value
item_eviction_freq_counter_age_threshold
and below a configured age item_eviction_age_percentage are not
evicted.

This avoids evicting "young" items; their MFU counter might not
reflect how hot they are yet as they were only recently stored.

However, when evicting from replica vbuckets, this may not be as
beneficial. As active resident ratio has a direct impact on cache miss
rate and average latency, it may be better to evict even young replica
items to reclaim memory where possible, before considering active vbs.

Change-Id: I3aaaa13e6a682000eb520e8971ad1451dbec7f48
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/134805
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine