## Summary In `LoaderState`, we record the already linked `Linkable`s to later record the `Usage` ```haskell -- compiler/GHC/Linker/Types.hs data LoaderState = LoaderState { bco_loader_state :: !BytecodeLoaderState -- ^ Information about bytecode objects we have loaded into the -- interpreter. , bcos_loaded :: !LinkableSet -- ^ The currently loaded interpreted modules (home package) , objs_loaded :: !LinkableSet -- ^ And the currently-loaded compiled modules (home package) , pkgs_loaded :: !PkgsLoaded -- ^ The currently-loaded packages; -- haskell libraries, system libraries, transitive dependencies , temp_sos :: ![(FilePath, String)] -- ^ We need to remember the name of previous temporary DLL/.so -- libraries so we can link them (see #10322) } ``` ```haskell -- -- | Find object files corresponding to the transitive closure of given home -- modules and direct object files for pkg dependencies mkObjectUsage :: PackageIfaceTable -> Plugins -> FinderCache -> HomeUnitGraph-> [Linkable] -> PkgsLoaded -> IO [Usage] mkObjectUsage pit plugins fc hug th_links_needed th_pkgs_needed = do ... ``` where we essentially use it to generate the appropriate `Usage` objects. Only specific fields of the `Linkable` are actually used to record the `Usage`, but a `Linkable` might hold on to a lot of memory. Thus, we propose to introduce a new `LinkableUsage` and `LinkablePartUsage` which only retains the details necessary to create the `Usage` object in `mkObjectUsage`. ```haskell type LinkableUsage = LinkableWith (NonEmpty LinkablePartUsage) -- | Record usage of a 'LinkablePart'. data LinkablePartUsage = FileLinkablePartUsage { flu_file :: !FilePath , flu_module :: !Module , flu_linkable_objs :: !(FlatBag OsPath) } | ByteCodeLinkablePartUsage { bclu_module :: !Module , bclu_hash :: !Fingerprint , bclu_linkable_objs :: !(FlatBag OsPath) } ``` This allows us to free `Linkable`s after they have been linked already. This should reduce memory usage of long-running GHC processes, for example when it is used as a build server. ## Environment * GHC version used: HEAD (4c58a3aecf8071bfcda6d0787652b89dec4a442f) * GHC 9.14.1