On Sun, 2011-09-04 at 09:53 +0800, Wu Fengguang wrote: > + * (o) bdi control lines > + * > + * The control lines for the global/bdi setpoints both stretch up to @limit. > + * The below figure illustrates the main bdi control line with an auxiliary > + * line extending it to @limit. > + * > + * o > + * o > + * o [o] main control line > + * o [*] auxiliary control line > + * o > + * o > + * o > + * o > + * o > + * o > + * o--------------------- balance point, rate scale = 1 > + * | o > + * | o > + * | o > + * | o > + * | o > + * | o > + * | o------- connect point, rate scale = 1/2 > + * | .* > + * | . * > + * | . * > + * | . * > + * | . * > + * | . * > + * | . * > + * [--------------------+-----------------------------.--------------------*] > + * 0 bdi_setpoint x_intercept limit > + * > + * The auxiliary control line allows smoothly throttling bdi_dirty down to > + * normal if it starts high in situations like > + * - start writing to a slow SD card and a fast disk at the same time. The SD > + * card's bdi_dirty may rush to many times higher than bdi_setpoint. > + * - the bdi dirty thresh drops quickly due to change of JBOD workload In light of the global control thing already having a hard stop at limit, what's the point of the auxiliary line? Why not simply run the bdi control between [0.5, 1.5] and leave it at that? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
