ProgressTracker was only freeing memory for work items when they reach
the head of the work tracking queue. If the first work item takes
hours to complete, and thousands of items are processed every second,
this leads to millions of completed items tracked in memory at a time,
wasting gigabytes of system RAM.
Rewrite ProgressHolderState methods to keep only incomplete work items
in memory, regardless of the order in which they are added or removed.
Also fix the unit tests which were relying on the memory leak to work,
and add test cases for code coverage.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
The task queue can become very large with many subvols, requiring hours
for the queue to clear. 'beescrawl.dat' saves in the meantime will save
the work currently scheduled, not the work currently completed.
Fix by tracking progress with ProgressTracker. ProgressTracker::begin()
gives the last completed crawl position. ProgressTracker::end() gives
the last scheduled crawl position. begin() does not advance if there
is any item between begin() and end() is not yet completed. In between
are crawled extents that are on the task queue but not yet processed.
The file 'beescrawl.dat' saves the begin() position while the extent
scanning task queue is fed from the end() position.
Also remove an unused method crawl_state_get() and repurpose the
operator<(BeesCrawlState) that nobody was using.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
