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From: Andrew Morton <akpm@linux-foundation.org>
To: Nick Piggin <npiggin@suse.de>
Cc: Linux Filesystems <linux-fsdevel@vger.kernel.org>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [rfc][patch 0/3] a faster buffered write deadlock fix?
Date: Fri, 9 Feb 2007 03:46:44 -0800	[thread overview]
Message-ID: <20070209034644.cc5fe40a.akpm@linux-foundation.org> (raw)
In-Reply-To: <20070209113116.GB11287@wotan.suse.de>

On Fri, 9 Feb 2007 12:31:16 +0100 Nick Piggin <npiggin@suse.de> wrote:

> > > > > 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??
> > > 
> > > That's the legacy path that uses prepare/commit (ie. supposing that all
> > > major filesystems did get converted to perform_write).
> > 
> > We'll never, ever, ever update and test all filesytems.  What you're
> > calling "legacy" code will be there for all time.
> 
> I didn't say all; I still prefer correct than fast;

For gawd's sake.  You can make the kernel less buggy by removing SMP
support.

Guess what?  Tradeoffs exist.

> you are still free
> to keep the fast-and-buggy code in the legacy path.

You make it sound like this is a choice.  It isn't.  Nobody is going to go
in and convert all those filesystems.

> > 
> > I haven't had time to look at the perform_write stuff yet.
> > 
> > > Of course I would still want my correct-but-slow version in that case,
> > > but I just wouldn't care to argue if you still wanted to keep it fast.
> > 
> > This is write().  We just cannot go and double-copy all the memory or take
> > mmap_sem and do a full pagetable walk in there.  It just means that we
> > haven't found a suitable solution yet.
> 
> You prefer speed over correctness even for little used filessytems, which
> is fine because I'm sick of arguing about it. The main thing for me is that
> important filesystems can be correct and fast.

I wouldn't characterise it as "arguing".  It's development.  Going and
sticking enormous slowdowns into write() to fix some bug which nobody is
hitting is insane.

We need to find a better fix, that's all.

  reply	other threads:[~2007-02-09 11:46 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-08 13:07 Nick Piggin
2007-02-08 13:07 ` [patch 1/3] fs: add an iovec iterator Nick Piggin
2007-02-08 19:49   ` Christoph Hellwig
2007-02-09  1:46     ` Nick Piggin
2007-02-09  2:03       ` Nate Diller
2007-02-09  3:31         ` Nick Piggin
2007-02-09 17:28           ` Zach Brown
2007-03-09 10:40         ` Christoph Hellwig
2007-02-08 23:04   ` Mark Fasheh
2007-02-08 13:07 ` [patch 2/3] fs: introduce perform_write aop Nick Piggin
2007-03-09 10:39   ` Christoph Hellwig
2007-03-09 12:52     ` Nick Piggin
2007-03-09 22:01       ` Anton Altaparmakov
2007-03-09 23:33     ` Mark Fasheh
2007-03-10  9:25       ` Christoph Hellwig
2007-03-12  2:13         ` Mark Fasheh
2007-03-14 13:30         ` Nick Piggin
2007-03-14 15:17           ` Christoph Hellwig
2007-02-08 13:07 ` [patch 3/3] ext2: use " Nick Piggin
2007-02-08 14:47   ` Dmitriy Monakhov
2007-02-09 19:14   ` Andrew Morton
2007-02-09 19:45     ` Andrew Morton
2007-02-10  1:34       ` Nick Piggin
2007-02-10  1:50         ` Andrew Morton
2007-02-09  0:38 ` [rfc][patch 0/3] a faster buffered write deadlock fix? Mark Fasheh
2007-02-09  2:04   ` Nick Piggin
2007-02-09  8:41 ` Andrew Morton
2007-02-09  9:54   ` Nick Piggin
2007-02-09 10:09     ` Andrew Morton
2007-02-09 10:32       ` Nick Piggin
2007-02-09 10:52         ` Andrew Morton
2007-02-09 11:31           ` Nick Piggin
2007-02-09 11:46             ` Andrew Morton [this message]
2007-02-09 12:11               ` Nick Piggin

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