What is the "shrinkd" in SQL Server logs?
This question was also asked in a comment on Paul Randal's blog Inside the Storage Engine: Ghost cleanup in depth

Paul replied:


  Looks like 
  
  a) you’ve got auto-shrink enabled for the database, or there’s an Agent job doing shrink
  b) you’ve had a lot of deletes, and the shrink ‘touched’ a lot of the pages with deleted records on so they got queued up for the ghost cleanup task to take care of.
  
  You need to fix a).


Feedback from the question author:


  When it happened again, I set dbcc traceon(661,-1) and the server resumed immediately. Why would there be so many ghostcleanup tasks suddenly without any shrink job? The answer: if the number of pages with ghosted rows is above the specified (hard-coded) limit, the task runs non-stop till the count comes down below the threshold value.