HEAD GHC+Cabal uses too much memory

If you install GHC HEAD and bootstrap cabal "2.0.0.0" as submoduled in that, whenever installing any packages cabal will hang for minutes before dependency resolution and will eat about 10 gigabytes of memory.

I did a simple profile,

COST CENTRE                                 MODULE                         SRC                                                 %time %alloc
packageListFromCache.readPackageDescription Distribution.Client.IndexUtils Distribution/Client/IndexUtils.hs:(714,5)-(722,61)   95.7   99.4

Trac metadata

Trac field	Value
Version	8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries (other)
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