On Mon 20-02-17 18:09:43, Laurent Dufour wrote: > On 20/02/2017 14:01, Michal Hocko wrote: > > On Wed 15-02-17 11:36:09, Laurent Dufour wrote: > >> The system may panic when initialisation is done when almost all the > >> memory is assigned to the huge pages using the kernel command line > >> parameter hugepage=xxxx. Panic may occur like this: > > > > I am pretty sure the system might blow up in many other ways when you > > misconfigure it and pull basically all the memory out. Anyway... > > > > [...] > > > >> This is a chicken and egg issue where the kernel try to get free > >> memory when allocating per node data in mem_cgroup_init(), but in that > >> path mem_cgroup_soft_limit_reclaim() is called which assumes that > >> these data are allocated. > >> > >> As mem_cgroup_soft_limit_reclaim() is best effort, it should return > >> when these data are not yet allocated. > > > > ... this makes some sense. Especially when there is no soft limit > > configured. So this is a good step. I would just like to ask you to go > > one step further. Can we make the whole soft reclaim thing uninitialized > > until the soft limit is actually set? Soft limit is not used in cgroup > > v2 at all and I would strongly discourage it in v1 as well. We will save > > few bytes as a bonus. > > Hi Michal, and thanks for the review. > > I'm not familiar with that part of the kernel, so to be sure we are on > the same line, are you suggesting to set soft_limit_tree at the first > time mem_cgroup_write() is called to set a soft_limit field ? yes > Obviously, all callers to soft_limit_tree_node() and > soft_limit_tree_from_page() will have to check for the return pointer to > be NULL. All callers that need to access the tree unconditionally, yes. Which is the case anyway, right? I haven't checked the check you have added is sufficient, but we shouldn't have that many of them because some code paths are called only when the soft limit is enabled. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
