On Tue, Apr 14, 2009 at 02:08:21PM -0400, Oren Laadan wrote: > > > Alexey Dobriyan wrote: > > On Tue, Apr 14, 2009 at 12:26:50AM -0400, Oren Laadan wrote: > >> Alexey Dobriyan wrote: > >>> On Thu, Apr 09, 2009 at 10:07:11PM -0700, Dave Hansen wrote: > >>>> I'm curious how you see these fitting in with the work that we've been > >>>> doing with Oren. Do you mean to just start a discussion or are you > >>>> really proposing these as an alternative to what Oren has been posting? > >>> Yes, this is posted as alternative. > >>> > >>> Some design decisions are seen as incorrect from here like: > >> A definition of "design" would help; I find most of your comments > >> below either vague, cryptic, or technical nits... > >> > >>> * not rejecting checkpoint with possible "leaks" from container > >> ...like this, for example. > > > > Like checkpointing one process out of many living together. > > See the thread on creating tasks in userspace vs. kernel space: > the argument here is that is an interesting enough use case for > a checkpoint of not-an-entire-container. > > Of course it will require more logic to it, so the user can choose > what she cares or does not care about, and the kernel could alert > the user about it. > > The point is, that it is, IMHO, a desirable capability. > > > > > If you allow this you consequently drop checks (e.g. refcount checks) > > for "somebody else is using structure to be checkpointed". > > > > From this point below, I totally agree with you that for the purpose > of a whole-container-checkpoint this is certainly desirable. My point > was that it can be easily added the existing patchset (not yours). > Why not add it there ? > > > If you drop these checks, you can't decipher legal sutiations like > > "process genuinely doesn't care about routing table of netns it lives in" > > from "illegal" situations like "process created shm segment but currently > > doesn't use it so not checkpointing ipcns will result in breakagenlater". > > > > You'll have to move responsibility to user, so user exactly knows what > > app relies on and on what. And probably add flags like CKPT_SHM, > > CKPT_NETNS_ROUTE ad infinitum. > > > > And user will screw it badly and complain: "after restart my app > > segfaulted". And user himself is screwed now: old running process is > > already killed (it was checkpointed on purpose) and new process in image > > segfaults every time it's restarted. > > > > All of this in out opinion results in doing C/R unreliably and badly. > > > > We are going to do it well and dig from the other side. > > > > If "leak" (any "leak") is detected, C/R is aborted because kernel > > doesn't know what app relies on and what app doesn't care about. > > > > This protected from situations and failure modes described above. > > > > This also protects to some extent from in-kernel changes where C/R code > > should have been updated but wasn't. Person doing incomplete change won't > > notice e.g refcount checks and won't try to "fix" them. But we'll notice it, > > e.g. when running testsuite (amen) and update C/R code accordingly. > > > > I'm talking about these checks so that everyone understands: > > > > for_each_cr_object(ctx, obj, CR_CTX_MM_STRUCT) { > > struct mm_struct *mm = obj->o_obj; > > unsigned int cnt = atomic_read(&mm->mm_users); > > > > if (obj->o_count != cnt) { > > printk("%s: mm_struct %p has external references %lu:%u\n", __func__, mm, obj->o_count, cnt); > > return -EINVAL; > > } > > } > > > > They are like moving detectors, small, invisible, something moved, you don't > > know what, but you don't care because you have to investigate anyway. > > > > In this scheme, if user wants to checkpoint just one process, he should > > start it alone in separate container. Right now, in posted patchset > > as cloned process with > > CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWNET > > So you suggest that to checkpoint a single process, say a cpu job that > would run a week, which runs in the topmost pid_ns, I will need to > checkpoint the entire topmost pid_ns (as a container, if at all possible > - surely there will non-checkpointable tasks there) and then in > user-space filter out the data and leave only one task, and then to > restart I'll use a container again ? No, you do little preparations and start CPU job in container from the very beginning. > Pffff ... why not just allow subtree checkpoint, not in a container, > with its well known limitations -- would work the same, for very little > additional implementation cost. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers