Re: [patch 3/6] mm: fix fault vs invalidate race for linear mappings

Andrew Morton
2007-03-07T07:08:52Z

On Wed, 7 Mar 2007 07:57:27 +0100 Nick Piggin <npiggin@suse.de> wrote:

> >
> > Why was truncate_inode_pages_range() altered to unmap the page if it got
> > mapped again?
> >
> > Oh. Because the unmap_mapping_range() call got removed from vmtruncate().
> > Why? (Please send suitable updates to the changelog).
>
> We have to ensure it is unmapped, and be prepared to unmap it while under
> the page lock.

But vmtruncate() dropped i_size, so nobody will map this page into
pagetables from then on.

> > I guess truncate of a mmapped area isn't sufficiently common to worry about
> > the inefficiency of this change.
>
> Yeah, and it should be more efficient for files that aren't mmapped,
> because we don't have to take i_mmap_lock for them.
>
> > Lots of memory barriers got removed in memory.c, unchangeloggedly.
>
> Yeah they were all for the lockless truncate_count checks. Now that
> we use the page lock, we don't need barriers.
>
> > Gratuitous renaming of locals in do_no_page() makes the change hard to
> > review. Should have been a separate patch.
> >
> > In fact, the patch would have been heaps clearer if that renaming had been
> > a separate patch.
>
> Shall I?

If you don't have anything better to do, yes please ;)