`GHC.Event.IntTable` uses a `ForeignPtr Int` to store the size of the table. This is bad because a lot of very small pinned bytestrings end up allocated which causes a significant amount of fragmentation. In my benchmark there were about 250 of these tables allocated which led to an additional 25 megablocks being retained. https://gitlab.haskell.org/ghc/ghc/-/blob/master/libraries/base/GHC/Event/IntTable.hs#L38 Locally I changed this to use an `IORef`, which significantly improved fragmentation in my benchmark because it no longer uses pinned memory. Is that the right fix?