Messages in this thread | | | Date | Mon, 11 Oct 1999 17:37:40 -0400 (EDT) | From | Alexander Viro <> | Subject | Re: locking question: do_mmap(), do_munmap() |
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On Mon, 11 Oct 1999, Manfred Spraul wrote:
> Alexander Viro wrote: > > > > On Mon, 11 Oct 1999, Stephen C. Tweedie wrote: > > > > > Hi, > > > > > > On Sun, 10 Oct 1999 15:03:45 -0400 (EDT), Alexander Viro > > > <viro@math.psu.edu> said: > > > > > > > Hold on. In swap_out_mm() you have to protect find_vma() (OK, it doesn't > > > > block, but we'll have to take care of mm->mmap_cache) _and_ you'll have to > > > > protect vma from destruction all way down to try_to_swap_out(). And to > > > > vma->swapout(). Which can sleep, so spinlocks are out of question > > > > here. > > > > > > No, spinlocks would be ideal. The vma swapout codes _have_ to be > > > prepared for the vma to be destroyed as soon as we sleep. In fact, the > > > entire mm may disappear if the process happens to exit. Once we know > > > which page to write where, the swapout operation becomes a per-page > > > operation, not per-vma. > > > > Aha, so you propose to drop it in ->swapout(), right? (after get_file() in > > filemap_write_page()... Ouch. Probably we'ld better lambda-expand the call > > in filemap_swapout() - the thing is called from other places too)... > > What about something like a rw-semaphore which protects the vma list: > vma-list modifiers [ie merge_segments(), insert_vm_struct() and > do_munmap()] grab it exclusive, swapper grabs it "shared, starve > exclusive". > All other vma-list readers are protected by mm->mmap_sem. > > This should not dead-lock, and no changes are required in > vm_ops->swapout().
What does it buy you over the simple semaphore here? Do you really see a contention scenario?
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