On Mon, 2008-08-04 at 22:44 +0200, Andrea Righi wrote: > 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. Fine in theory, hard in practice. :) I think the best we can hope for is to keep parity with what happens in the rest of the kernel. We already have a problem today with people mmap()'ing lots of memory and dirtying it all at once. Adding a i/o bandwidth controller or a memory controller isn't really going to fix that. I think it is outside the scope of the i/o (and memory) controllers until we solve it generically, first. -- Dave -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
