On Fri, Jan 20 2017 at 10:19am -0500, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote: > Hou Tao <houtao1@xxxxxxxxxx> writes: > > > Hi all, > > > > We need to throttle the O_DIRECT IO on data and metadata device > > of a dm-thin pool and encounter some problems. If we set the > > limitation on the root blkcg, the throttle works. If we set the > > limitation on a child blkcg, the throttle doesn't work well. > > > > The reason why the throttle doesn't work is that dm-thin defers > > the process of bio when the physical block of bio has not been > > allocated. The bio will be submitted by the pool worker, and the > > blkcg of the bio will be the blkcg of the pool worker, namely, > > the root blkcg instead of the blkcg of the original IO thread. > > We only set a limitation on the blkcg of the original IO thread, > > so the blk-throttle doesn't work well. > > > > In order to handle the situation, we add a "keep_bio_blkcg" feature > > to dm-thin. If the feature is enabled, the original blkcg of bio > > will be saved at thin_map() and will be used during blk-throttle. > > Why is this even an option? I would think that you would always want > this behavior. Right, shouldn't be an optional feature. Also, this implementation is very dm-thin specific. I still have this line of work on my TODO because there should be a more generic way to wire up these associations in either block core or DM core. Now that there is both dm-crypt and dm-thin specific RFC patches to fix this I'll see about finding a solution that works for both but that is more generic. Not sure how quickly I'll get to this but I'll do my best. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
