Cray experienced slowness clearing the lustre caches after job termination. This slowness is a result of clearing the caches for each namespace in series. Lustre should provide a high-level procfs interface which clears lustre caches across namespaces in parallel and returns when all caches are cleared.

The interface should be at /proc/fs/lustre/ldlm/drop_caches, and when written to, it must clear all lustre caches in parallel and return when finished.

It must have the same effect as the following, but in parallel:

for LRU in $(ls /proc/fs/lustre/ldlm/namespaces/*osc*/lru_size); do
    echo clear > $LRU
done

for LRU in $(ls /proc/fs/lustre/ldlm/namespaces/*mdc*/lru_size); do
    echo clear > $LRU
done