Multi-tier CacheLib part 2 #357
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This is the implementation logic for the background eviction (and promotion when multi-tier is enabled). The main parameters for the background workers are the number of threads, `backgroundMoverThreads` and the batch size used `backgroundEvictionBatch`, which configures the number of items to evict in batch (while holding the container lock), and `backgroundTargetFree` which sets target free percentage of each class. The background workers will work to keep that percentage of space free. The main result is that SET (allocate) latencies are significantly reduced - kvcache workload with 40GB DRAM, ampFactor set to 200 via the trace replayer. Throughput set at 1.2M ops/sec. | Percentile | % Improvement | |------------|---------------| | 0.50000 | 70.4 | | 0.90000 | 23.0 | | 0.99000 | 12.2 | | 0.99900 | 89.7 | | 0.99990 | 24.9 | | 0.99999 | 0.6 | The GET (find) latencies are unaffected by the background workers as long as the batch size remains reasonably small (10 in our tests).
This includes printing: - allocSize - allocated memory size - memory usage fraction
Part 1. ----------------------------------------- This includes the following: - Multi-tier allocator with TierId - allocateInternalTier - creating multi-tier allocator on shared memory - serialization - some basic tests - Add option to insert items to first free tier, this enables an interleaving approach. Ther is no data movement among the tiers. Use `insertToFirstFreeTier` option to control. In order to evict data from the second tier, you will need to have the background movers enabled.
Part 2. ---------------------------- This patch introduces tryEvictToNextMemoryTier (the actual data movement), multi-tier stats and some additional multi-tier tests. - Includes MM2Q support for promotion
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Multi-tier allocator patch part 2 introduces eviction and promotion among the tiers, the multi-tier stats and some additional multi-tier tests. With this setup tier 1 and tier 2 are exclusive L1 and L2 caches respectively.
We have introduced some optimizations to reduce the overhead of the data movement:
evictIfNotAccessedoption.