[PATCH 4.4 61/66] bcache: correct cache_dirty_target in __update_writeback_rate()

4.4-stable review patch. If anyone has any objections, please let me know. -- From: Tang Junhui commit a8394090a9129b40f9d90dcb7f4a49d60c727ca6 upstream. __update_write_rate() uses a Proportion-Differentiation Controller algorithm to control writeback

[PATCH 4.4 61/66] bcache: correct cache_dirty_target in __update_writeback_rate()

4.4-stable review patch. If anyone has any objections, please let me know. -- From: Tang Junhui commit a8394090a9129b40f9d90dcb7f4a49d60c727ca6 upstream. __update_write_rate() uses a Proportion-Differentiation Controller algorithm to control writeback rate. A dirty target