Repro for GHC making crazy amounts of slop with +RTS -N2, see https://gitlab.haskell.org/ghc/ghc/-/issues/18849

SlopProblem.hs

-- Run with:
--     ghc --make -O -threaded -fforce-recomp SlopProblem.hs && command time ./SlopProblem +RTS -N1 -s
--
-- My output with ghc 8.6.5 on a 4-core machine:
--    ...
--    336,707,456 bytes maximum residency (14 sample(s))
--    611,774,592 bytes maximum slop
--    ...
--    ... 1716344maxresident)k
-- The slop reduces to 1 MB when `-N1` is used, and the resident memory usage
-- measured by `time` reduces from 1.7 GB to 0.6 GB.

import qualified Data.Vector as V


data WordTuple = WordTuple {-# UNPACK #-} !Int {-# UNPACK #-} !Int


main :: IO ()
main = do
  putStrLn "Measuring 1M WordTuples"
  V.fromList
    [ WordTuple (fromIntegral (i+1)) (fromIntegral (i+2))
    | i <- [1..10000000::Int]
    ]
    `seq`
    return ()