Hi, > > >> 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. Yes, that's right. This should be solved. But there is a good thing when you use a memory controller. A problem occurred in a certain cgroup will be confined in its cgroup. I think this is a great point, don't you think? Thank you, Hirokazu Takahashi. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
