On Mon, 9 Jul 2018, Michal Hocko wrote: > > Blockable mmu notifiers and mlocked memory is not the extent of the > > problem, if a process has a lot of virtual memory we must wait until > > free_pgtables() completes in exit_mmap() to prevent unnecessary oom > > killing. For implementations such as tcmalloc, which does not release > > virtual memory, this is important because, well, it releases this only at > > exit_mmap(). Of course we cannot do that with only the protection of > > mm->mmap_sem for read. > > And how exactly a timeout helps to prevent from "unnecessary killing" in > that case? As my patch does, it becomes mandatory to move MMF_OOM_SKIP to after free_pgtables() in exit_mmap() and then repurpose MMF_UNSTABLE to indicate that the oom reaper should not operate on a given mm. In the event we cannot reach MMF_OOM_SKIP, we need to ensure forward progress and that is possible with a timeout period in the very rare instance where additional memory freeing is needed, and without unnecessary oom killing when it is not needed.
