unused --remote: Reduced memory use to 1/4th what was used before.

Using a single strictness annotation, in just the right place.
Tried several others, none of which helped and some of which potentially
hurt. This is only the second time I've really had to deal with this in
a year of using haskell, which is, I suppose not that bad.

1 files changed, 4 insertions, 1 deletions

diff --git a/Command/Unused.hs b/Command/Unused.hs
index e7065b3c3..27f5af1b4 100644
--- a/Command/Unused.hs
+++ b/Command/Unused.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
+{-# LANGUAGE BangPatterns #-}
+
 module Command.Unused where
 
 import Control.Monad (filterM, unless, forM_)
@@ -80,7 +82,8 @@ checkRemoteUnused' r = do
 	where
 		isthere k = do
 			us <- keyLocations k
-			return $ uuid `elem` us
+			let !there = uuid `elem` us
+			return there
 		uuid = Remote.uuid r
 
 writeUnusedFile :: FilePath -> [(Int, Key)] -> Annex ()