On Wed, Mar 02, 2016 at 10:19:38PM +0200, Nikolay Borisov wrote: > On Wednesday, March 2, 2016, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > > On Wed, Mar 02, 2016 at 09:59:13PM +0200, Nikolay Borisov wrote: > > > On Wednesday, March 2, 2016, Vivek Goyal <vgoyal@xxxxxxxxxx > > <javascript:;>> wrote: > > > > > > > On Wed, Mar 02, 2016 at 08:03:10PM +0200, Nikolay Borisov wrote: > > > > > Thanks for the patch I will likely have time to test this sometime > > next > > > > week. > > > > > But just to be sure - the expected behavior would be that processes > > > > > writing to dm-based devices would experience the fair-shair > > > > > scheduling of CFQ (provided that the physical devices that back those > > > > > DM devices use CFQ), correct? > > > > > > > > Nikolay, > > > > > > > > I am not sure how well it will work with CFQ of underlying device. It > > will > > > > get cgroup information right for buffered writes. But cgroup > > information > > > > > > > > > Right, what's your definition of buffered writes? > > > > Writes which go through page cache. > > > > > My mental model is that > > > when a process submits a write request to a dm device , the bio is going > > to > > > be put on a devi e workqueue which would then be serviced by a > > background > > > worker thread and later the submitter notified. Do you refer to this > > whole > > > gamut of operations as buffered writes? > > > > No, once the bio is submitted to dm device it could be a buffered write or > > a direct write. > > > > > > > > for reads and direct writes will come from submitter's context and if dm > > > > layer gets in between, then many a times submitter might be a worker > > > > thread and IO will be attributed to that worker's cgroup (root cgroup). > > > > > > > > > Be that as it may, proivded that the worker thread is in the 'correct' > > > cgroup, then the appropriate babdwidth policies should apply, no? > > > > Worker thread will most likely be in root cgroup. So if a worker thread > > is submitting bio, it will be attributed to root cgroup. > > > > We had similar issue with IO priority and it did not work reliably with > > CFQ on underlying device when dm devices were sitting on top. > > > > If we really want to give it a try, I guess we will have to put cgroup > > info of submitter early in bio at the time of bio creation even for all > > kind of IO. Not sure if it is worth the effort. > > > > For the case of IO throttling, I think you should put throttling rules on > > the dm device itself. That means as long as filesystem supports the > > cgroups, you should be getting right cgroup information for all kind of > > IO and throttling should work just fine. > > > Throttling does work even now, but the use case I had in mind was > proportional > distribution of IO. Imagine 50 or so dm devices, hosting IO intensive > workloads. In > this situation, I'd be interested each of them getting proportional IO > based on the weights > set in the blkcg controller for each respective cgroup for every workload. > I see what you are trying to do. Carry the cgroup information from top to bottom of IO stack for all kind of IO. I guess we also need to call bio_associate_current() when dm accepts bio from the submitter. Thanks Vivek -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
