[GHC] #10470: Allocating StablePtrs leads to GC slowdown even after they're freed

[GHC]

#10470: Allocating StablePtrs leads to GC slowdown even after they're freed
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        Reporter:  bitonic           |                   Owner:  simonmar
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Runtime System    |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Description changed by bitonic:

Old description:

> If we allocate and then free a lot of StablePtrs the GC performance will
> be degrated for the rest of the execution.
>
> I have attached a program that performs a GC-heavy task (foldr'ing a long
> list of Ints) before and after allocating and then freeing a million
> StablePtrs.  After the StablePtrs are freed the task takes more than
> twice as long.
>
> The reason for this is that {{stable_ptr_table}} in {{Stable.c}} is never
> resized, and is looped over for every GC pause.

New description:

 If we allocate and then free a lot of StablePtrs the GC performance will
 be degrated for the rest of the execution.

 I have attached a program that performs a GC-heavy task (foldr'ing a long
 list of Ints) before and after allocating and then freeing a million
 StablePtrs.  After the StablePtrs are freed the task takes more than twice
 as long.

 The reason for this is that `stable_ptr_table` in `Stable.c` is never
 resized, and is looped over for every GC pause.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10470#comment:1>
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