On Thu, 7 Nov 2019, Maged Mokhtar wrote: > > > On 07/11/2019 21:09, Mike Snitzer wrote: > > On Thu, Nov 07 2019 at 1:55pm -0500, > > Maged Mokhtar <mmokhtar@xxxxxxxxxxx> wrote: > > > > > > > > > > > On 06/11/2019 17:08, Mike Snitzer wrote: > > > > On Tue, Nov 05 2019 at 4:19pm -0500, > > > > Maged Mokhtar <mmokhtar@xxxxxxxxxxx> wrote: > > > > > > > > > Gentle ping please. > > > > > > > > > > It could add flexibility in changing cache parameters after device > > > > > creation. > > > > > > > > I'm inclined to _not_ take this type of change. > > > > > > > > Why isn't changing the config parameters via table reload viable for > > > > you? > > > > > > > > > > > > > Hi Mike, > > > > > > Thank you for your response. The main issue is to enable setting > > > some config parameters while the device is mounted and running and > > > avoid calling target ctr() by sending parameter changes via > > > messages. A similar setup was used in dm-cache. > > > > > > The reason is that tuning the write cache may require run time > > > changes. If un-tuned we can observes periods of spikes and/or step > > > like disk utilization on the slow device during writeback using > > > iostat, and these spikes correspond to periods of increased client > > > io latency. Utilization can be tuned by varying the number of active > > > writeback jobs + the gap between high and low marks to achieve a > > > smooth high utilization. Such tuning is difficult to do when > > > creating the cache device as it depends on the hardware and io > > > workload. We are hoping to use some userspace monitoring and tuning > > > tool to periodically adjust these values while the device is > > > running. > > > > I think you're missing that any actively used DM device can be > > suspended, table reloaded, resumed. So the tuning at runtime is still > > possible, it just requires more steps. > > > > And I'm saying that unless/until there is a better reason other than > > "dm-cache allowed tuning via messages" I'm not interested in having > > multiple methods for tuning dm-writecache. > > > > Mike > > > just for my understanding, does not table reload call _ctr() and > re-initializes things like threads/read metadada ..? Yes it does. But you don't have to unmount the filesystem when you reload the table. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
