だけはTo do all that one can, As much or many ~ as one could

だけは is another one of the many grammar patterns in Japanese that includes the particle だけ, meaning 'just' or 'only'. In this particular structure, だけ pairs with は, and presents a specific verb as the topic to indicate that it is being done 'as much as one can'. The same verb will be repeated both before and after だけは, with the one coming second usually appearing in its past-tense or ている form.

Imagining that the target verb was 食(た)べる 'to eat', the literal translation of something like 食(た)べるだけは食(た)べた would be 'I ate just what I could eat'. Because this pattern frequently discusses possibilities, it is also very common for the first verb to be in the potential れる or られる form.