On 12/05/2010 01:44 AM, Wu Fengguang wrote:
I noticed that my NFSROOT test system goes slow responding when there is heavy dd to a local disk. Traces show that the NFSROOT's bdi_limit is near 0 and many tasks in the system are repeatedly stuck in balance_dirty_pages(). There are two related problems: - light dirtiers at one device (more often than not the rootfs) get heavily impacted by heavy dirtiers on another independent device - the light dirtied device does heavy throttling because bdi_limit=0, and the heavy throttling may in turn withhold its bdi_limit in 0 as it cannot dirty fast enough to grow up the bdi's proportional weight. Fix it by introducing some "low pass" gate, which is a small (<=8MB) value reserved by others and can be safely "stole" from the current global dirty margin. It does not need to be big to help the bdi gain its initial weight.
Makes a lot of sense to me. Acked-by: Rik van Riel <riel@xxxxxxxxxx> -- All rights reversed -- 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
