Making bigram features from a particular dataset
Bigram is better to be used with sentences. In your case, files contain a list of words, as I could understand. Therefore using bigrams in your project might not yield expecting results. However, if you are still willing to do that, this is how you calculate bigrams:

Take the list of words and count the frequencies of adjacent words. 
Ex:

(madvise, write) - 1

(write, write) -  3

(write, read) -  1

(read, read) -  1

(read, madvise) -  1

.

.

.

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(sendto, epoll_pwait) -  1