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

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Date:	Fri, 9 Feb 2007 10:54:05 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linux Filesystems <linux-fsdevel@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [rfc][patch 0/3] a faster buffered write deadlock fix?

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@...e.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, 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), 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).

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 ;)

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