Hi, Andrea, I'm working with Ryo on dm-ioband and other stuff. > > On Mon, 2008-08-04 at 20:22 +0200, Andrea Righi wrote: > >> But I'm not yet convinced that limiting the IO writes at the device > >> mapper layer is the best solution. IMHO it would be better to throttle > >> applications' writes when they're dirtying pages in the page cache (the > >> io-throttle way), because when the IO requests arrive to the device > >> mapper it's too late (we would only have a lot of dirty pages that are > >> waiting to be flushed to the limited block devices, and maybe this could > >> lead to OOM conditions). IOW dm-ioband is doing this at the wrong level > >> (at least for my requirements). Ryo, correct me if I'm wrong or if I've > >> not understood the dm-ioband approach. > > > > The avoid-lots-of-page-dirtying problem sounds like a hard one. But, if > > you look at this in combination with the memory controller, they would > > make a great team. > > > > The memory controller keeps you from dirtying more than your limit of > > pages (and pinning too much memory) even if the dm layer is doing the > > throttling and itself can't throttle the memory usage. > > mmh... but in this way we would just move the OOM inside the cgroup, > that is a nice improvement, but the main problem is not resolved... The concept of dm-ioband includes it should be used with cgroup memory controller as well as the bio cgroup. The memory controller is supposed to control memory allocation and dirty-page ratio inside each cgroup. Some guys of cgroup memory controller team just started to implement the latter mechanism. They try to make each cgroup have a threshold to limit the number of dirty pages in the group. I feel this is good approach since each functions can work independently. > A safer approach IMHO is to force the tasks to wait synchronously on > each operation that directly or indirectly generates i/o. > > In particular the solution used by the io-throttle controller to limit > the dirty-ratio in memory is to impose a sleep via > schedule_timeout_killable() in balance_dirty_pages() when a generic > process exceeds the limits defined for the belonging cgroup. I guess it would make the memory controller team guys happier if you can help them design their dirty-page ratio controlling functionality much cooler and more generic. I think their goal is almost the same as yours. > Limiting read operations is a lot more easy, because they're always > synchronized with i/o requests. > > -Andrea Thank you, Hirokazu Takahashi. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
