我在弄清楚如何在Statemonad 中运行的模拟中减少内存使用和 GC 时间时遇到了一些麻烦。目前我必须运行编译后的代码+RTS -K100M以避免堆栈空间溢出，并且 GC 统计数据非常可怕（见下文）。
以下是相关的代码片段。可以在http://hpaste.org/68527找到完整的、有效的 (GHC 7.4.1) 代码。
-- Lone algebraic data type holding the simulation configuration.
data SimConfig = SimConfig {
numDimensions :: !Int -- strict
, numWalkers :: !Int -- strict
, simArray :: IntMap [Double] -- strict spine
, logP :: Seq Double -- strict spine
, logL :: Seq Double -- strict spine
, pairStream :: [(Int, Int)] -- lazy (infinite) list of random vals
, doubleStream :: [Double] -- lazy (infinite) list of random vals
} deriving Show
-- The transition kernel for the simulation.
simKernel :: State SimConfig ()
simKernel = do
config <- get
let arr = simArray config
let n = numWalkers config
let d = numDimensions config
let rstm0 = pairStream config
let rstm1 = doubleStream config
let lp = logP config
let ll = logL config
let (a, b) = head rstm0 -- uses random stream
let z0 = head . map affineTransform $ take 1 rstm1 -- uses random stream
where affineTransform a = 0.5 * (a + 1) ^ 2
let proposal = zipWith (+) r1 r2
where r1 = map (*z0) $ fromJust (IntMap.lookup a arr)
r2 = map (*(1-z0)) $ fromJust (IntMap.lookup b arr)
let logA = if val > 0 then 0 else val
where val = logP_proposal + logL_proposal - (lp `index` (a - 1)) - (ll `index` (a - 1)) + ((fromIntegral n - 1) * log z0)
logP_proposal = logPrior proposal
logL_proposal = logLikelihood proposal
let cVal = (rstm1 !! 1) <= exp logA -- uses random stream
let newConfig = SimConfig { simArray = if cVal
then IntMap.update (\_ -> Just proposal) a arr
else arr
, numWalkers = n
, numDimensions = d
, pairStream = drop 1 rstm0
, doubleStream = drop 2 rstm1
, logP = if cVal
then Seq.update (a - 1) (logPrior proposal) lp
else lp
, logL = if cVal
then Seq.update (a - 1) (logLikelihood proposal) ll
else ll
}
put newConfig
main = do
-- (some stuff omitted)
let sim = logL $ (`execState` initConfig) . replicateM 100000 $ simKernel
print sim
就堆而言，配置文件似乎暗示System.Random除了 之外的函数(,)是内存的罪魁祸首。我不能直接包含图像，但您可以在此处查看堆配置文件：http: //i.imgur.com/5LKxX.png。
我不知道如何进一步减少这些东西的存在。随机变量是在Statemonad 外部生成的（以避免在每次迭代时拆分生成器），并且我相信在从模拟配置中包含的惰性列表 ( ) 中提取一对时会出现(,)内部的唯一实例。simKernelpairStream
包括GC在内的统计数据如下：
1,220,911,360 bytes allocated in the heap
787,192,920 bytes copied during GC
186,821,752 bytes maximum residency (10 sample(s))
1,030,400 bytes maximum slop
449 MB total memory in use (0 MB lost due to fragmentation)
Tot time (elapsed) Avg pause Max pause
Gen 0 2159 colls, 0 par 0.80s 0.81s 0.0004s 0.0283s
Gen 1 10 colls, 0 par 0.96s 1.09s 0.1094s 0.4354s
INIT time 0.00s ( 0.00s elapsed)
MUT time 0.95s ( 0.97s elapsed)
GC time 1.76s ( 1.91s elapsed)
EXIT time 0.00s ( 0.00s elapsed)
Total time 2.72s ( 2.88s elapsed)
%GC time 64.9% (66.2% elapsed)
Alloc rate 1,278,074,521 bytes per MUT second
Productivity 35.1% of total user, 33.1% of total elapsed
再一次，我必须提高最大堆栈大小才能运行模拟。我知道某处一定有一个大笨蛋……但我不知道在哪里？
在这样的问题中，如何改进堆/堆栈分配和 GC？我怎样才能确定一个 thunk 可能在哪里建立？这里使用Statemonad 是不是被误导了？
--
更新：
编译时我忽略了查看分析器的输出-fprof-auto。这是该输出的开头：
COST CENTRE MODULE no. entries %time %alloc %time %alloc
MAIN MAIN 58 0 0.0 0.0 100.0 100.0
main Main 117 0 0.0 0.0 100.0 100.0
main.randomList Main 147 1 62.0 55.5 62.0 55.5
main.arr Main 142 1 0.0 0.0 0.0 0.0
streamToAssocList Main 143 1 0.0 0.0 0.0 0.0
streamToAssocList.go Main 146 5 0.0 0.0 0.0 0.0
main.pairList Main 137 1 0.0 0.0 9.5 16.5
consPairStream Main 138 1 0.7 0.9 9.5 16.5
consPairStream.ys Main 140 1 4.3 7.8 4.3 7.8
consPairStream.xs Main 139 1 4.5 7.8 4.5 7.8
main.initConfig Main 122 1 0.0 0.0 0.0 0.0
logLikelihood Main 163 0 0.0 0.0 0.0 0.0
logPrior Main 161 5 0.0 0.0 0.0 0.0
main.sim Main 118 1 1.0 2.2 28.6 28.1
simKernel Main 120 0 4.8 5.1 27.6 25.8
我不确定如何准确解释这一点，但随机双打的懒惰流randomList让我畏缩。我不知道如何改进。