[GHC] #15348: Enable two-step allocator on FreeBSD

[GHC]

#15348: Enable two-step allocator on FreeBSD
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  FreeBSD           |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4939
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"8736715857d08cc1f88d766c257b39c05df20639/ghc"
 87367158/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8736715857d08cc1f88d766c257b39c05df20639"
 rts: Enable two-step allocator on FreeBSD

 Previously we would prevent any operating system not providing the
 MEM_NORESERVE flag
 from using the two-step allocator. Afterall, Linux will reserve
 swap-space for
 a mapping unless this flag is given, which is most certainly not what
 we want.

 However, it seems that FreeBSD provides the reservation-only mapping
 behavior
 that we expect despite not providing the MEM_NORESERVE macro. In fact,
 it
 provided the macro until 2014, when it was removed on account of not
 being
 implemented in the kernel. However, empirical evidence suggests that
 just plain
 mmap does what we want.

 Reviewers: erikd, simonmar

 Subscribers: rwbarton, thomie, erikd, carter

 GHC Trac Issues: #15348

 Differential Revision: https://phabricator.haskell.org/D4939
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15348#comment:6>
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