fb64 commented on code in PR #1334: URL: https://github.com/apache/arrow-java/pull/1334#discussion_r4194088988
########## memory/memory-ffm/src/main/java/org/apache/arrow/memory/ffm/FfmAllocationManager.java: ########## @@ -0,0 +1,72 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +package org.apache.arrow.memory.ffm; + +import java.lang.foreign.Arena; +import java.lang.foreign.MemorySegment; +import org.apache.arrow.memory.AllocationManager; +import org.apache.arrow.memory.ArrowBuf; +import org.apache.arrow.memory.BufferAllocator; +import org.apache.arrow.memory.ReferenceManager; + +/** Allocation manager based on the Foreign Function & Memory API. */ +public final class FfmAllocationManager extends AllocationManager { + + private static final Arena EMPTY_ARENA = Arena.ofShared(); + private static final ArrowBuf EMPTY = + new ArrowBuf(ReferenceManager.NO_OP, null, 0, EMPTY_ARENA.allocate(0).address()); + + public static final AllocationManager.Factory FACTORY = + new Factory() { + @Override + public AllocationManager create(BufferAllocator accountingAllocator, long size) { + return new FfmAllocationManager(accountingAllocator, size); + } + + @Override + public ArrowBuf empty() { + return EMPTY; + } + }; + + private final Arena arena; + private final long allocatedSize; + private final long allocatedAddress; + + FfmAllocationManager(BufferAllocator accountingAllocator, long requestedSize) { + super(accountingAllocator); + this.arena = Arena.ofShared(); Review Comment: Thanks, nice catch @jbonofre, you were right! Benchmark and results: https://gist.github.com/fb64/334d2eeb14e1e4c5adbff6e38e9f3b7e Using one shared Arena per buffer makes allocation about 100x slower than Unsafe, and it gets worse with more JVM threads (4 KiB: Unsafe 89 ns vs FFM 8.8 µs, and 58.8 µs with 256 idle threads). I also prototyped a version that allocates with malloc/free downcalls and keeps the same FFM accessor: it matches Unsafe on every workload, including vector growth and batch building. So memory access isn't the issue, only the per-buffer arena. This doesn't weaken safety: the FFM accessor already accesses memory through new global segments built from the buffer's raw address, not through the arena's segment, so closing the arena never protected against use-after-free. Arrow's protection comes from ArrowBuf's reference count checks, which don't change. Unlike `Arena.allocate`, malloc also doesn't zero the memory, which matches the Unsafe and Netty managers. I propose to update this PR with a malloc/free implementation based on the [foreign linker](https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/foreign/Linker.html) instead of one shared Arena per buffer. Does that sound good? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
