#7831: Bad fragmentation when allocating many large objects -------------------------------------+------------------------------------ Reporter: ezyang | Owner: ezyang Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Runtime System | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Changes (by simonmar): * cc: simonmar (added) Comment: josef: O'Caml is a bit different, the situation there is fragmentation in the heap itself because the old-generation collector doesn't move objects. We don't have that issue in GHC, at least for small objects, but there's a related issue in the layer beneath the GC (the block allocator) that Edward's program nicely illustrates here. I doubt this is ever an issue in practice. The fragmentation that arises this way is bounded: at worst the fragmentation will be equal to the amount of memory used for large objects. And in most cases (a) it will be less than this because the sizes of large objects are never exactly 0.5MB, and (b) the fragmented space will be used to store small objects, so it won't be wasted. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7831#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler