ports/rp2: Raise GC stack size for PSRAM.

GC stack was overflowing and causing the GC to scan through the
entire memory pool, which is a particularly pathological case
with 8MB PSRAM. This caused noticable slowdowns during GC.

This change takes the stack from 256 to 4096 bytes to avoid
overflow.

Co-authored-by: Kirk Benell <[email protected]>
Signed-off-by: Phil Howard <[email protected]>

Author: Gadgetoid

ports/rp2/mpconfigport.h

@@ -78,6 +78,7 @@
 // Memory allocation policies
 #if MICROPY_HW_ENABLE_PSRAM
 #define MICROPY_GC_STACK_ENTRY_TYPE             uint32_t
+#define MICROPY_ALLOC_GC_STACK_SIZE             (1024) // Avoid slowdown when GC stack overflow causes a full sweep of PSRAM-backed heap
 #else
 #define MICROPY_GC_STACK_ENTRY_TYPE             uint16_t
 #endif