On Thu, Sep 19, 2019 at 10:33:10AM +0800, Lin Feng wrote: > On 9/18/19 20:33, Michal Hocko wrote: > > I absolutely agree here. From you changelog it is also not clear what is > > the underlying problem. Both congestion_wait and wait_iff_congested > > should wake up early if the congestion is handled. Is this not the case? > > For now I don't know why, codes seem should work as you said, maybe I need to > trace more of the internals. > But weird thing is that once I set the people-disliked-tunable iowait > drop down instantly, this is contradictory to the code design. Yes, this is quite strange. If setting a smaller timeout makes a difference, that indicates we're not waking up soon enough. I see two possibilities; one is that a wakeup is missing somewhere -- ie the conditions under which we call clear_wb_congested() are wrong. Or we need to wake up sooner. Umm. We have clear_wb_congested() called from exactly one spot -- clear_bdi_congested(). That is only called from: drivers/block/pktcdvd.c fs/ceph/addr.c fs/fuse/control.c fs/fuse/dev.c fs/nfs/write.c Jens, is something supposed to be calling clear_bdi_congested() in the block layer? blk_clear_congested() used to exist until October 29th last year. Or is something else supposed to be waking up tasks that are sleeping on congestion?
