Dave Hansen wrote: > 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... 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. Limiting read operations is a lot more easy, because they're always synchronized with i/o requests. -Andrea -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
