Re: [Haskell-cafe] Measuring memory usage

Hi Vlatko, I don't get the same numbers with ghc-datasize recursiveSize $! xs1 -- 240 (list of length 1) recursiveSize $! xs30 -- 6296 compiled on GHC 8.0.2 with optimizations (-O) whereas recursiveSizeNF gives me the size of the thunk (force xs1), which depends on whether xs1 is evaluated or not. The size of X is missing: - 1 word for the X constructor - 5 words for the fields (they are not unpacked, this must be explicitly required with the {-# UNPACK #-} pragma) - 8B for one of the text fields (which for some reason takes 64B instead of 56B) That's 56B extra, for a total of 224B. Add in 4W for a singleton list and that's 256B. Why are 16B missing in the above 240B figure? Note that in mkX, there are two fields equal to (Uid i), so they get shared (recursiveSize doesn't recount shared structures). (It's hardly an optimization: if we take out the newtypes, the code looks like X {a = i, b = i, ...}, so the compiler simply puts the same pointer in the two fields.) Notice also that nullary constructors (in particular Yes/No) will always be shared. The compiler may also float out the whole "Left Yes" and "Right No" to the toplevel, further reducing the size of longer lists. gsize counts constructors. In particular, each newtype constructor counts as one, and primitives like Int and Char also count as one (the value they box is not visible to Data), and Text has a dummy Data instance to make it seem like a newtype around [Char]. You can use this snippet to see a trace of the generic traversal: everywhereM (\x -> print (dataTypeOf x) >> return x) xs1 Finally, "weigh" counts allocations, which are generally a superset of the actual space taken by a data structure once it is fully computed. Li-yao On 07/04/2018 07:12 AM, Vlatko Basic wrote:

Hello again,

I'm still trying to find some method to predict memory usage and came upon this page: https://wiki.haskell.org/GHC/Memory_Footprint

I tried to manually calculate how much memory will the record below consume (64-bit, 1W = 8B):

newtype Id   = Id    Text deriving (Generic, Data, NFData) -- = 6W newtype Uid  = Uid   Int  deriving (Generic, Data, NFData) -- = 2W newtype XUid = XUid  Uid  deriving (Generic, Data, NFData) -- = 2W newtype YUid = YUid  Uid  deriving (Generic, Data, NFData) -- = 2W data    Dir  = Yes | No   deriving (Generic, Data)         -- = 2W

data X = X   { a :: XUid                -- =  2W       -- Int   , b :: YUid                -- =  2W       -- Int   , c :: Id                  -- =  6W + 8B  -- Text len 4   , d :: Either Dir Dir      -- =  1W + 2W  -- Either + Dir + No/Yes   , e :: Text                -- =  6W + 8B  -- Text len 4   } deriving (Generic, Data) -- = 19W + 16B = 152 + 16 = 168B

and calculated the assumed sizes of few lists with different number of elements:

Expected list sizes    ([v] = (1 + 3N) words + N * sizeof(v))   30: 1 + 3W *   30 + (19W *   30 + 16 *   30) =   5,761 B  600: 1 + 3W *  600 + (19W *  600 + 16 *  600) = 115,201 B 5000: 1 + 3W * 5000 + (19W * 5000 + 16 * 5000) = 960,001 B

I also compared these sizes with three libs (Data.Generics.Schemes.gsize, GHC.DataSize.recursiveSizeNF, Weigh) and the results were:

#items recursiveSizeNF gSize      Weigh    Expected  Diff/recursiveSizeNF    1:            1,416       18        696 168          -   30:            8,008      931     20,880 5,761        28%  600:          135,688   18,601    417,600 115,201        15% 5000:        1,121,288  155,001  3,480,000 960,001        14%

As you can see, the results are more than surprising (to me), with recursiveSizeNF coming closest. They all measure the same variable.

What am I missing?

For completeness, here are relevant parts of code for creating elements (with excessive forcing):

  let mkX i = force X{ a = XUid $ Uid i                      , b = YUid $ Uid i                      , c = Id $ tshow i                      , d = if even i then (Left Yes) else (Right No)                      , e = T.reverse (tshow i)                      }       xs30  = force . map mkX $ take   30 $ randomRs (1000,1030) (mkStdGen 0)       xs600 = force . map mkX $ take  600 $ randomRs (1000,1600) (mkStdGen 0)       xs5K  = force . map mkX $ take 5000 $ randomRs (1000,5000) (mkStdGen 0)

  dataSize <- recursiveSizeNF $!! {a}   let gSize = gsize $!! mkX 0

...

-------- Original Message -------- Subject: Measuring memory usage From: Vlatko Basic To: haskell-cafe Date: 29/06/18 14:31

Hello,

I've come to some strange results using Weigh package.

It shows that HashMap inside 'data' is using much, much more memory.

The strange thing is that I'm seeing too large mem usage in my app as well (several "MapData" like in records), and trying to figure out with 'weigh' what's keeping the mem.

Noticed that when I change the code to use HashMap directly (not inside 'data', that's the only change), the mem usage observed with top drops down for ~60M, from 850M to 790M.

These are the test results for 10K, 5K and 3.3K items for "data MapData k v = MapData (HashMap k v)" (at the end is the full runnable example.)

Case           Allocated  GCs HashMap          262,824    0 HashMap half      58,536    0 HashMap third     17,064    0 MapData        4,242,208    4

I tested by changing the order, disabling all but one etc., and the results were the same. Same 'weigh' behaviour with IntMap and Map.

So, if anyone knows and has some experience with such issues, my questions are:

1. Is 'weigh' package reliable/usable, at least to some extent? (the results do show diff between full, half and third)

2. How do you measure mem consumptions of your large data/records?

3. If the results are even approximately valid, what could cause such large discrepancies with 'data'?

4. Is there a way to see if some record has been freed from memory, GCed?

module Main where

import Prelude

import Control.DeepSeq     (NFData) import Data.HashMap.Strict (HashMap, fromList) import GHC.Generics        (Generic) import Weigh               (mainWith, value)

data MapData k v = MapData (HashMap k v) deriving Generic instance (NFData k, NFData v) => NFData (MapData k v)

full, half, third :: Int full  = 10000 half  =  5000 third =  3333

main :: IO () main = mainWith $ do   value "HashMap"       (          mkHMList full)   value "HashMap half"  (          mkHMList half)   value "HashMap third" (          mkHMList third)   value "MapData"       (MapData $ mkHMList full)

mkHMList :: Int -> HashMap Int String mkHMList n = fromList . zip [1..n] $ replicate n "some text"

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