Think of it as an NMT upgrade.
Here's an example of what the output should look like:
https://developer.ibm.com/answers/questions/288697/why-
does-nativememinfo-in-javacore-show-incorrect.html?sort=oldest
- Adam
I think NMT walks the stack, so we should get allocation points grouped by
call stacks. Provided we have symbols loaded for the native library using
Unsafe.allocateMemory(), this should give us too a fine granularity. But I
have not yet tested this in practice. Maybe Zhengyu knows more.
Quick test shows this call site:
[0x00007f8558b26243] Unsafe_AllocateMemory0+0x93
[0x00007f8537b085cb]
(malloc=2KB type=Internal #1)
I will take a look why there is a frame not decoded.
Thanks,
-Zhengyu
..Thomas
David
On 14/02/2018 9:32 PM, Adam Farley8 wrote:
Hi All,
Currently, diagnostic core files generated from OpenJDK seem to lump
all
of the
native memory usages together, making it near-impossible for someone
to
figure
out *what* is using all that memory in the event of a memory leak.
The OpenJ9 VM has a feature which allows it to track the allocation of
native
memory for Direct Byte Buffers (DBBs), and to supply that information
into
the
cores when they are generated. This makes it a *lot* easier to find
out
what is using
all that native memory, making memory leak resolution less like some
dark
art, and
more like logical debugging.
To use this feature, there is a native method referenced in
Unsafe.java.
To open
up this feature so that any VM can make use of it, the java code below
sets the
stage for it. This change starts letting people call DBB-specific
methods
when
allocating native memory, and getting into the habit of using it.
Thoughts?
Best Regards
Adam Farley
P.S. Code:
diff --git
a/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template
b/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template
---
a/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template
+++
b/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template
@@ -85,7 +85,7 @@
// Paranoia
return;
}
- UNSAFE.freeMemory(address);
+ UNSAFE.freeDBBMemory(address);
address = 0;
Bits.unreserveMemory(size, capacity);
}
@@ -118,7 +118,7 @@
long base = 0;
try {
- base = UNSAFE.allocateMemory(size);
+ base = UNSAFE.allocateDBBMemory(size);
} catch (OutOfMemoryError x) {
Bits.unreserveMemory(size, cap);
throw x;
diff --git a/src/java.base/share/classes/jdk/internal/misc/Unsafe.java
b/src/java.base/share/classes/jdk/internal/misc/Unsafe.java
--- a/src/java.base/share/classes/jdk/internal/misc/Unsafe.java
+++ b/src/java.base/share/classes/jdk/internal/misc/Unsafe.java
@@ -632,6 +632,26 @@
}
/**
+ * Allocates a new block of native memory for DirectByteBuffers,
of
the
+ * given size in bytes. The contents of the memory are
uninitialized;
+ * they will generally be garbage. The resulting native pointer
will
+ * never be zero, and will be aligned for all value types.
Dispose
of
+ * this memory by calling {@link #freeDBBMemory} or resize it
with
+ * {@link #reallocateDBBMemory}.
+ *
+ * @throws RuntimeException if the size is negative or too large
+ * for the native size_t type
+ *
+ * @throws OutOfMemoryError if the allocation is refused by the
system
+ *
+ * @see #getByte(long)
+ * @see #putByte(long, byte)
+ */
+ public long allocateDBBMemory(long bytes) {
+ return allocateMemory(bytes);
+ }
+
+ /**
* Resizes a new block of native memory, to the given size in
bytes.
The
* contents of the new block past the size of the old block are
* uninitialized; they will generally be garbage. The resulting
native
@@ -687,6 +707,27 @@
}
/**
+ * Resizes a new block of native memory for DirectByteBuffers, to
the
+ * given size in bytes. The contents of the new block past the
size
of
+ * the old block are uninitialized; they will generally be
garbage.
The
+ * resulting native pointer will be zero if and only if the
requested
size
+ * is zero. The resulting native pointer will be aligned for all
value
+ * types. Dispose of this memory by calling {@link
#freeDBBMemory},
or
+ * resize it with {@link #reallocateDBBMemory}. The address
passed
to
+ * this method may be null, in which case an allocation will be
performed.
+ *
+ * @throws RuntimeException if the size is negative or too large
+ * for the native size_t type
+ *
+ * @throws OutOfMemoryError if the allocation is refused by the
system
+ *
+ * @see #allocateDBBMemory
+ */
+ public long reallocateDBBMemory(long address, long bytes) {
+ return reallocateMemory(address, bytes);
+ }
+
+ /**
* Sets all bytes in a given block of memory to a fixed value
* (usually zero).
*
@@ -918,6 +959,17 @@
checkPointer(null, address);
}
+ /**
+ * Disposes of a block of native memory, as obtained from {@link
+ * #allocateDBBMemory} or {@link #reallocateDBBMemory}. The
address
passed
+ * to this method may be null, in which case no action is taken.
+ *
+ * @see #allocateDBBMemory
+ */
+ public void freeDBBMemory(long address) {
+ freeMemory(address);
+ }
+
/// random queries
/**
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IBM United Kingdom Limited - Registered in England and Wales with
number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
