On Wed, Sep 13, 2017 at 02:01:29PM -0700, Shaohua Li wrote: > From: Shaohua Li <shli@xxxxxx> > > loop block device handles IO in a separate thread. The actual IO > dispatched isn't cloned from the IO loop device received, so the > dispatched IO loses the cgroup context. > > I'm ignoring buffer IO case now, which is quite complicated. Making the > loop thread aware cgroup context doesn't really help. The loop device > only writes to a single file. In current writeback cgroup > implementation, the file can only belong to one cgroup. > > For direct IO case, we could workaround the issue in theory. For > example, say we assign cgroup1 5M/s BW for loop device and cgroup2 > 10M/s. We can create a special cgroup for loop thread and assign at > least 15M/s for the underlayer disk. In this way, we correctly throttle > the two cgroups. But this is tricky to setup. > > This patch tries to address the issue. We record bio's css in loop > command. When loop thread is handling the command, we then use the API > provided in patch 1 to set the css for current task. The bio layer will > use the css for new IO (from patch 3). > > Signed-off-by: Shaohua Li <shli@xxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Thanks. -- tejun
