On 20/02/2017 18:42, Michal Hocko wrote: > 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. You're right there are not so much callers to fix. I'll send a new series containing the previous patch fixing the initial panic and another one delaying the data allocation. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
