Michal Hocko wrote: > > > Can we try a simpler way and get back to what I was suggesting before > > > [1] and simply not play tricks with > > > down_write(&mm->mmap_sem); > > > up_write(&mm->mmap_sem); > > > > > > and use the write lock in exit_mmap for oom_victims? > > > > You mean something like this? > > or simply hold the write lock until we unmap and free page tables. That increases possibility of __oom_reap_task_mm() giving up reclaim and setting MMF_OOM_SKIP when exit_mmap() is making forward progress, doesn't it? I think that it is better that __oom_reap_task_mm() does not give up when exit_mmap() can make progress. In that aspect, the section protected by mmap_sem held for write should be as short as possible. > It would make the locking rules much more straightforward. > What you are proposing is more focused on this particular fix and it > would work as well but the subtle locking would still stay in place. Yes, this change is focused on -stable patch. > I am not sure we want the trickiness. I don't like the trickiness too. I think we can even consider direct OOM reaping suggested at https://patchwork.kernel.org/patch/10095661/ . > > > Then, I'm tempted to call __oom_reap_task_mm() before holding mmap_sem for write. > > It would be OK to call __oom_reap_task_mm() at the beginning of __mmput()... > > I am not sure I understand. To reduce possibility of __oom_reap_task_mm() giving up reclaim and setting MMF_OOM_SKIP.
