#3941: GC: excess of reserved space for bitmaps in case of mark/compact/sweep
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Reporter: gabrielrf | Owner:
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Runtime System | Version: 6.10.4
Resolution: invalid | Keywords:
Difficulty: | Os: Unknown/Multiple
Testcase: | Architecture: Unknown/Multiple
Failure: None/Unknown |
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Changes (by simonmar):
* status: new => closed
* resolution: => invalid
Comment:
I think you're incorrect. The bitmap requires 1 bit per word of heap,
which is
{{{
1 bit per word
== 1 bit per sizeof(W_) bytes
== 8 bits per 8*sizeof(W_) bytes
}}}
so to get the number of bytes in the bitmap, we divide the number of bytes
in the heap by `8*sizeof(W_)`, which is what the calculation does.
The later calculation you referred to is in terms of words, because the
variable `bitmap` has type `StgWord *`, and pointer arithmetic in C is in
units of the pointed-to type.
So I believe if you try to make the change you suggest, the result will be
a resounding segfault. Please try it!
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3941#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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