Re: [patch] mm: bug in set_page_dirty_buffers

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2006-10-10 at 07:22 +0200, Nick Piggin wrote:
> On Mon, Oct 09, 2006 at 10:01:27PM -0700, Andrew Morton wrote:
> > On Tue, 10 Oct 2006 06:47:45 +0200
> > Nick Piggin <npiggin@suse.de> wrote:
> > > > There we can trylock all the pages and bale if any fail.
> > > 
> > > Hmm, try_to_unmap is OK because the page is already locked. page_remove_rmap
> > > isn't allowed to fail.
> > 
> > I was talking about try_to_unmap_cluster().
> 
> But page_remove_rmap's many callers are still screwed. Take do_wp_page,
> for example.

> > It can probably be made to work.  But a sane interface is "when dinking
> > with page internals, lock the page".
> 
> I disagree because it will lead to horrible hacks because many callers
> can't sleep. If anything I would much prefer an innermost-spinlock in
> page->flags that specifically excludes truncate. Actually tree_lock can
> do that now, provided we pin mapping in all callers to set_page_dirty
> (which we should do).

Yeah, but we're hard working to eradicate tree lock; I have ran into
this problem before; that is, zap_pte_range and co. not being able to
lock the page. I'd really like to see that fixed.

In my current concurrent pagecache patches I've abused your PG_nonewrefs
and made it this page internal (bit)spinlock, but it just doesn't look
nice to have both this lock and PG_locked.


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