That's not so good. Could you please post your vm settings, in particular (mine are in brackets):

/proc/sys/vm/dirty_ratio (8)
/proc/sys/vm/dirty_background_ratio (4)
/proc/sys/vm/swappiness (0)
/proc/sys/vm/vfs_cache_pressure (1000)
/proc/sys/vm/overcommit_memory (2)
/proc/sys/vm/overcommit_ratio (100)
/proc/sys/vm/oom_kill_allocating_task (1)
/proc/sys/vm/min_free_kbytes (4096)

It's probably also worth checking the /sys/block/mmcblk0/queue settings, such as read_ahead_kb (512), nr_requests (32) and scheduler (cfq). I have tweaked the iosched folder settings underneath that to match the ones posted by freemangordon here (my page_cluster is the default of 5 however and I don't think nr_requests needs to be so high). Finally I have some schedtool settings too but I doubt they would help to fix your problems.