Re: locking question: do_mmap(), do_munmap()

Alexander Viro
1999-10-11T16:05:23Z

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)...