[PATCH] RFR Bug-pending: Enable Hotspot to Track Native Memory Usage for Direct Byte Buffers

[David Holmes]

On 14/02/2018 10:43 PM, David Holmes wrote:
> Adding in core-libs-dev as there's nothing related to hotspot directly 
> here.

Correction, this is of course leading to a proposed change in hotspot to 
implement the new Unsafe methods and perform the native memory tracking. 
Of course we already have NMT so the obvious question is how this will 
fit in with NMT?

David

> 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
>>       /**
>>
>> Unless stated otherwise above:
>> IBM United Kingdom Limited - Registered in England and Wales with number
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>>