displayio memory loss

code.py

import board
import os
import gc
import time
import random
import displayio
from adafruit_display_shapes.rect import Rect

def overwrite_bitmap(xw, yh, gmin, gmax):
    x = random.randrange(0, xw)
    y = random.randrange(0, yh)
    c = random.randrange(0x000000, 0x1000000)
    w = random.randrange(1, 33)
    h = w
    rect = Rect(x, y, w, h, fill=c)
    splash[random.randrange(gmin, gmax)] = rect

starttime = time.monotonic()

with open('/VERSIONS.txt') as f:
    cp_lib_bundle = f.readline().strip()

SCREENWIDTH = 320
SCREENHEIGHT = 240
SPLASHMAX = 250
splash = displayio.Group(max_size=SPLASHMAX)
print("splash len:", end=" ")
print(len(splash), end=" ")
for i in range(0, SPLASHMAX):
    splash.append(displayio.TileGrid(displayio.Bitmap(1, 1, 1), 
                                     pixel_shader=displayio.Palette(1)))
print(len(splash))

board.DISPLAY.show(splash)

loop = 0
snap = time.monotonic()
while True:
    overwrite_bitmap(SCREENWIDTH, SCREENHEIGHT, 0, SPLASHMAX)
    elapsed = time.monotonic() - snap
    if (elapsed >= 60):  # every minute or so
        snap = time.monotonic()
        print(os.uname()[4].split()[1] + 
              os.uname()[4].split()[2].replace('with', ''), end=" ")  # machine
        print(os.uname()[3], end=" ")  # CircuitPython version
        print("CPLIB=%s" % cp_lib_bundle, end=" ")
        print("Loop=%0i" % loop, end=" ")
        print("Up=%0.3fs" % time.monotonic(), end=" ")
        print("Run=%0.3fs" % (time.monotonic() - starttime), end=" ")
        print("Mem=%0ib" % gc.mem_free(), end=" ")
        print("%s" % gc.collect(), end=" ")
        print("Mem=%0ib" % gc.mem_free(), end=" ")
        print()
    loop += 1

Actually, updating to latest (03f9048 on 2019-04-19) from 4.0.0-beta7 seems to have slowed or stabilized the loss.

The initial drops in free memory could easily be attributable to the simple initial TileGrids getting replaced with the more complex main loop TileGrids. In 4.0.0-beta7, the loss would continue at a similar rate for hours until a MemoryException occurred, but the latest circuitpython 03f9048, with gc fixes included, seems to have stopped the memory loss.