base: make Foreign.Marshal.Pool use RTS internal arena for allocation

`Foreign.Marshal.Pool` used to call `malloc` once for each allocation
request. Each `Pool` maintained a list of allocated pointers, and
traverses the list to `free` each one of those pointers. The extra O(n)
overhead is apparently bad for a `Pool` that serves a lot of small
allocation requests.

This patch uses the RTS internal arena to implement `Pool`, with these
benefits:

- Gets rid of the extra O(n) overhead.
- The RTS arena is simply a bump allocator backed by the block
  allocator, each allocation request is likely faster than a libc
  `malloc` call.

Closes #14762 #18338.

1 files changed, 3 insertions, 3 deletions

diff --git a/rts/Arena.h b/rts/Arena.h
index 49298713ab..8a7b304a7a 100644
--- a/rts/Arena.h
+++ b/rts/Arena.h
@@ -10,13 +10,13 @@
 typedef struct _Arena Arena;
 
 // Start a new arena
-RTS_PRIVATE Arena * newArena   ( void );
+Arena * newArena   ( void );
 
 // Allocate memory in an arena
-RTS_PRIVATE void  * arenaAlloc ( Arena *, size_t );
+void  * arenaAlloc ( Arena *, size_t );
 
 // Free an entire arena
-RTS_PRIVATE void arenaFree  ( Arena * );
+void arenaFree  ( Arena * );
 
 // For internal use only:
 RTS_PRIVATE unsigned long arenaBlocks( void );