On Tue 26-06-18 18:03:34, Yang Shi wrote: > > > On 6/26/18 12:43 AM, Peter Zijlstra wrote: > > On Mon, Jun 25, 2018 at 05:06:23PM -0700, Yang Shi wrote: > > > By looking this deeper, we may not be able to cover all the unmapping range > > > for VM_DEAD, for example, if the start addr is in the middle of a vma. We > > > can't set VM_DEAD to that vma since that would trigger SIGSEGV for still > > > mapped area. > > > > > > splitting can't be done with read mmap_sem held, so maybe just set VM_DEAD > > > to non-overlapped vmas. Access to overlapped vmas (first and last) will > > > still have undefined behavior. > > Acquire mmap_sem for writing, split, mark VM_DEAD, drop mmap_sem. Acquire > > mmap_sem for reading, madv_free drop mmap_sem. Acquire mmap_sem for > > writing, free everything left, drop mmap_sem. > > > > ? > > > > Sure, you acquire the lock 3 times, but both write instances should be > > 'short', and I suppose you can do a demote between 1 and 2 if you care. > > Thanks, Peter. Yes, by looking the code and trying two different approaches, > it looks this approach is the most straight-forward one. Yes, you just have to be careful about the max vma count limit. -- Michal Hocko SUSE Labs
