From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Sender: Tejun Heo Date: Wed, 13 Sep 2017 14:42:27 -0700 From: Tejun Heo To: Shaohua Li Cc: linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, lizefan@huawei.com, tglx@linutronix.de, kernel-team@fb.com, axboe@kernel.dk, Shaohua Li Subject: Re: [PATCH V2 4/4] block/loop: make loop cgroup aware Message-ID: <20170913214226.GD378890@devbig577.frc2.facebook.com> References: <2f16f7a5176195bc70a2c10dd7fa11ea85b9145f.1505335620.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <2f16f7a5176195bc70a2c10dd7fa11ea85b9145f.1505335620.git.shli@fb.com> List-ID: On Wed, Sep 13, 2017 at 02:01:29PM -0700, Shaohua Li wrote: > From: Shaohua Li > > 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 Acked-by: Tejun Heo Thanks. -- tejun