[PATCH] blkparse: drastically reduce memory foot print

[PATCH] blkparse: drastically reduce memory foot print

File reads needed enough memory to hold all events from all CPUs.
This quickly grew to hundreds of megabytes. Bring down this number
by interleaving reads from the files and relying on the same
mechanism as the piped reads to syncronize them. This makes file reads
use the same path as pipes and actually removes more code than it adds.
For a 900,000 entry file, memory consumption here is down from ~110MiB
from about 1MiB to process it.