Consider:

    private void socketWrite(byte b[], int off, int len) throws IOException {
        if (!VMJFR.socketWriteToken.isEnabled()) {
            socketWrite(b, off, len);
            return;
        }
        SocketWriteEvent event = new SocketWriteEvent(VMJFR.socketWriteToken);
        int bytesWritten = -1;
        try {
            event.begin();
            socketWrite(b, off, len);
            bytesWritten = len;
        } finally {
            String hostString = impl.address.toString();
            int delimiterIndex = hostString.lastIndexOf('/');

            event.host = hostString.substring(0, delimiterIndex);
            event.address = hostString.substring(delimiterIndex + 1);
            event.port = impl.port;
            event.bytesWritten = bytesWritten;

            event.commit();
        }
    }

We can avoid the address.toString() and String manipulations if we check event.shouldWrite() before.