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From: Nick Piggin <npiggin@suse.de>
To: Andrew Morton <akpm@linux-foundation.org>
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 13:11:18 +0100	[thread overview]
Message-ID: <20070209121118.GA510@wotan.suse.de> (raw)
In-Reply-To: <20070209034644.cc5fe40a.akpm@linux-foundation.org>

On Fri, Feb 09, 2007 at 03:46:44AM -0800, Andrew Morton wrote:
> On Fri, 9 Feb 2007 12:31:16 +0100 Nick Piggin <npiggin@suse.de> wrote:
> 
> > > 
> > > 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.

I'm talking about known bugs.

> Guess what?  Tradeoffs exist.

I agree that 60% is much too big of a hit for all filesystems. Which is
why I propose this new aop.

> > 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.

IMO, once all the maintained filesystems are converted then it would be
a good choice to make. You think otherwise and I won't argue.

> > > 
> > > 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.

Actually I'm doing this because I try to fix real data corruption problems
which people are hitting. You told me I can't get those fixes in until I
fix this problem.

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

I actually found perform_write to be a speedup. And if perform_write is
merged then I would be happy to not fix the prepare_write path, or wait for
someone to come up with a better fix.

      reply	other threads:[~2007-02-09 12:11 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
2007-02-09 12:11               ` Nick Piggin [this message]

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