寻找JVM堆的分配

html5 • • 问答

我已经运行了straced JVM（OpendJDK 11）：

strace -e trace=mmap java -Xms8192m Main

输出是：

mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7effda5fa000
mmap(NULL, 2158880, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effda1c3000
mmap(0x7effda3d1000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xe000) = 0x7effda3d1000
mmap(NULL, 246024, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7effda5bd000
mmap(NULL, 4131552, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd9dd2000
mmap(0x7effda1b9000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1e7000) = 0x7effda1b9000
mmap(0x7effda1bf000, 15072, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7effda1bf000
mmap(NULL, 2212016, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd9bb5000
mmap(0x7effd9dd0000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b000) = 0x7effd9dd0000
mmap(NULL, 2109712, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd99b1000
mmap(0x7effd9bb3000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7effd9bb3000
mmap(NULL, 2221184, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd9792000
mmap(0x7effd99ab000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x19000) = 0x7effd99ab000
mmap(0x7effd99ad000, 13440, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7effd99ad000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7effda5bb000
mmap(NULL, 21206808, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd8358000
mmap(0x7effd963f000, 1032192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x10e7000) = 0x7effd963f000
mmap(0x7effd973b000, 354072, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7effd973b000
mmap(NULL, 246024, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7effda5bd000
mmap(NULL, 3702848, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd7fcf000
mmap(0x7effd8348000, 49152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x179000) = 0x7effd8348000
mmap(0x7effd8354000, 12352, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7effd8354000
mmap(NULL, 3789144, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd7c31000
mmap(0x7effd7fcd000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x19c000) = 0x7effd7fcd000
mmap(NULL, 2192432, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7effd7a19000
mmap(0x7effd7c2f000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x16000) = 0x7effd7c2f000
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7effda4ba000
+++ exited with 0 +++

我将堆的初始大小设置为 8192M，并尝试在 strace 的输出中找到堆的分配。我找不到。为什么？

回答

添加-f选项（跟踪子进程）。

在原始线程中运行 Java 代码会导致很多问题，详见JDK-6316197。

java 启动器在一个新线程中创建一个 JVM。

以上是寻找JVM堆的分配的全部内容。
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