odraese commented on a change in pull request #626: [HIVE-21686] ensure that
memory allocator does not evict using brute …
URL: https://github.com/apache/hive/pull/626#discussion_r283427024
##########
File path:
llap-server/src/java/org/apache/hadoop/hive/llap/cache/BuddyAllocator.java
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@@ -48,6 +48,24 @@
import org.apache.hadoop.hive.llap.metrics.LlapDaemonCacheMetrics;
import org.apache.hadoop.hive.ql.io.orc.encoded.StoppableAllocator;
+/**
+ *
+ * High level description, functionality and the memory layout.
+ * Allocation can be of general size but it will be rounded to the next power
of 2.
+ * Allocation smaller than size {@link ConfVars#LLAP_ALLOCATOR_MIN_ALLOC} will
be rounded to min allocation size.
+ * Allocation bigger than size {@link ConfVars#LLAP_ALLOCATOR_MAX_ALLOC} will
throw exceptions.
+ * Allocator slices memory slab called {@code arenas} to carve out byte
buffers using slice and position.
+ *
+ * Each {@code arena} has array of {@code freeList} used for concurrency
management and to index free buffers by size.
+ * |
+ * Each {@code arena} has a max Size {@link BuddyAllocator#MAX_ARENA_SIZE} 1GB.
+ * \_
+ * Each arena is divided into chunks of max allocation size {@link
ConfVars#LLAP_ALLOCATOR_MAX_ALLOC} default 16MB
+ * \_
+ * Each chunk of {@code maxAllocationSize} is sliced using the classical
Buddy Allocator algorithm.
+ * \_
+ * Each Buddy Allocator tree can be split up to chunk of size {@link
ConfVars#LLAP_ALLOCATOR_MIN_ALLOC} 4KB
Review comment:
chunk -> chunks
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