sdhci_pci0: <Generic SD HCI> ... slot(s) allocated
mmc0: <MMC/SD bus> on sdhci_pci0
mmcsd0: 256MB <SD Memory Card> at mmc0 26MHz/4bit
$ sysctl hw.mmcrace.action=13
mmcrace: SUSPEND on mmcsd0 (kills task, suspend=1: strategy keeps queueing)
mmcrace: suspend -> 0
$ for i in $(seq 96); do (dd if=/dev/mmcsd0 of=/dev/null bs=4m count=4 &); done
$ vmstat | head -3
 r   b w   fre   flt   re   pi   po   fr ...
 1  96 0 3.20G  247K    0 552K  12K 596M ...   # 96 blocked, ~400MB+ pinned, paging
$ sysctl hw.mmcrace.action=14
mmcrace: RESUME on mmcsd0 (restarts task)
mmcrace: resume -> 0
# every bio was queued consumerless (no bound, no ENXIO); DF-4783 witnessed the
# endgame under heavier pressure: 'panic: malloc limit exceeded'