[GHC] #15980: unpin a mutable byte array
#15980: unpin a mutable byte array -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Sometimes, it necessary to allocate a mutable byte array as pinned. This commonly happens when the mutable byte array will immidiately be handed over to a `safe` FFI routine to be initialized. However, after it has been initialized, it might not be useful for it to be pinned anymore. If it's a little byte array, it may contribute to a fragmented heap. Even if it's large, the fact that the user explicitly asked pin it prohibits it from ever being added to a compact region (pinned bytearrays that were pinned simply because they are over 3KB can be added to compact regions). A workaround for either of these problems is to copy the pinned bytearray into an unpinned byte array afterwards. But that's kind of wasteful. Is it possible to have a primop {{{ unpinMutableByteArray :: MutableByteArray s -> State# s -> State# s }}} After this, the mutable byte array could be moved in memory. This would require `isMutableByteArrayPinned#` to undergo a similar transition as `sizeofMutableByteArray#` (which was superceeded by `getSizeofMutableByteArray#`) underwent. Is this possible? Or are pinned things allocated in a special place that makes unpinning impossible? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15980 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15980: unpin a mutable byte array -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by carter): Hrrrmm. Do you have any examples where you can create excessive fragmentation? That’d be worth a ticket. One issue I see with adding such a primop is that it won’t be possible to respect alignment constraints that may have been expressed at bytearray allocation time. For unaligned bytearrays, you could just copy the buffer over to an unpinned array then copy it into the compact region -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15980#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15980: unpin a mutable byte array -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by carter): Pinned byte arrays also live in a different world than normal heap objects. So unpinning would be he same as a copy afaict. Which you can easily do in user space already -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15980#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15980: unpin a mutable byte array -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by andrewthad): Yeah, the fact that they live in a separate part of the heap seems pretty damning. I think I'll just have to accept that this cannot be done. At least, not without large changes to GHC's runtime. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15980#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15980: unpin a mutable byte array -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: task | Status: closed Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 Resolution: wontfix | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by andrewthad): * status: new => closed * resolution: => wontfix -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15980#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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