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

[Adam Farley8]

> Adding in core-libs-dev as there's nothing related to hotspot directly 
here.
>
> David

Thought it was best to pass this through hotspot lists first, as full 
completion
of the native side of things will probably require hotspot changes.

You're quite right though, I should have cc'd hotspot *and* core libs.

- Adam

>
> 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
>> 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