From: Wu Fengguang<fengguang.wu@xxxxxxxxx>
Fix "system goes unresponsive under memory pressure and lots of
dirty/writeback pages" bug.
In the above thread, Andreas Mohr described that
Invoking any command locked up for minutes (note that I'm
talking about attempted additional I/O to the _other_,
_unaffected_ main system HDD - such as loading some shell
binaries -, NOT the external SSD18M!!).
This happens when the two conditions are both meet:
- under memory pressure
- writing heavily to a slow device