presto-main/src/main/java/io/prestosql/memory/QueryContext.java/QueryContext/updateRevocableMemory
class QueryContext:    private synchronized ListenableFuture<?> updateRevocableMemory(String allocationTag, long delta)
    {
        if (delta >= 0) {
            return memoryPool.reserveRevocable(queryId, delta);
        }
        memoryPool.freeRevocable(queryId, -delta);
        return NOT_BLOCKED;
    }