Re: [rfc][patch 0/3] a faster buffered write deadlock fix?

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 9 Feb 2007 10:54:05 +0100 Nick Piggin <npiggin@suse.de> wrote:

> On Fri, Feb 09, 2007 at 12:41:01AM -0800, Andrew Morton wrote:
> > On Thu,  8 Feb 2007 14:07:15 +0100 (CET) Nick Piggin <npiggin@suse.de> wrote:
> > 
> > > So I have finally finished a first slightly-working draft of my new aops
> > > op (perform_write) proposal. I would be interested to hear comments about
> > > it.  Most of my issues and concerns are in the patch headers themselves,
> > > so reply to them.
> > > 
> > > The patches are against my latest buffered-write-fix patchset.
> > 
> > What happened with Linus's proposal to instantiate the page as pinned,
> > non-uptodate, unlocked and in pagecache while we poke the user address?
> 
> That's still got a deadlock,

It does?

>  and also it doesn't work if we want to lock
> the page when performing a minor fault (which I want to fix fault vs
> invalidate),

It's hard to discuss this without a description of what you want to fix
there, and a description of how you plan to fix it.

> and also assumes nobody's ->nopage locks the page or
> requires any resources that are held by prepare_write (something not
> immediately clear to me with the cluster filesystems, at least).

The nopage handler is filemap_nopage().  Are there any exceptions to that?

> But that all becomes legacy path, so do we really care? Supposing fs
> maintainers like perform_write, then after the main ones have implementations
> we could switch over to the slow-but-correct prepare_write legacy path.
> Or we could leave it, or we could use Linus's slightly-less-buggy scheme...
> by that point I expect I'd be sick of arguing about it ;)

It's worth "arguing" about.  This is write().  What matters more??