• Simon Marlow's avatar
    Run C finalizers incrementally during mutation · f7bbc343
    Simon Marlow authored
    With a large heap it's possible to build up a lot of finalizers
    between GCs.  We've observed GC spending up to 50% of its time running
    finalizers.  But there's no reason we have to run finalizers during
    GC, and especially no reason we have to block *all* the mutator
    threads while *one* GC thread runs finalizers one by one.
    
    I thought about a bunch of alternative ways to handle this, which are
    documented along with runSomeFinalizers() in Weak.c.  The approach I
    settled on is to have a capability run finalizers if it is idle.  So
    running finalizers is like a low-priority background thread. This
    requires some minor scheduler changes, but not much.  In the future we
    might be able to move more GC work into here (I have my eye on freeing
    large blocks, for example).
    
    Test Plan:
    * validate
    * tested on our system and saw reductions in GC pauses of 40-50%.
    
    Reviewers: bgamari, niteria, osa1, erikd
    
    Reviewed By: bgamari, osa1
    
    Subscribers: rwbarton, thomie, carter
    
    Differential Revision: https://phabricator.haskell.org/D4521
    f7bbc343
Weak.h 589 Bytes