Messages in this thread | | | Date | Tue, 26 Jun 2018 09:43:44 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping |
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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.
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