Hello, On Fri, Jan 05, 2018 at 01:16:26PM +0800, xuejiufei wrote: > From: Jiufei Xue <jiufei.xjf@xxxxxxxxxxxxxxx> > > Cgroup writeback is supported since v4.2. But there exists a problem > in the following case. > > A cgroup may send both buffer and direct/sync IOs. The foreground > thread will be stalled when periodic writeback IOs is flushed because > the service queue in block throttle layer already has a plenty of > writeback IOs, then foreground IOs should be enqueued with its FIFO > policy. The current policy is dispatching 6 reads and 2 writes during > each round, sync writes will be significantly delayed. > > This patch adds another queue in block throttle. Now there are 3 queues > in a service queue: read, sync write, async write, and we can dispatch > more sync writes than aync writes. We usually handle sync writes together with reads instead of introducing a separate queue for sync writes. Thanks. -- tejun
