linux-kernel - Re: [PATCH 0/8][RFC] IO latency/throughput fixes

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Date:	Tue, 7 Apr 2009 12:36:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ray Lee <ray-lk@...rabbit.org>, Hua Zhong <hzhong@...il.com>,
	Theodore Tso <tytso@....edu>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/8][RFC] IO latency/throughput fixes


* Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> On Tue, Apr 7, 2009 at 01:10, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> > On Mon, 6 Apr 2009, Linus Torvalds wrote:
> >> thing that we think people would be happiest with.
> >>
> >> I think "ordered" was a reasonable default, but that was at least partly
> >> because _both_ ordered and writeback sucked (partly in different ways).
> >>
> >> I do think we could make it a config option.
> >
> > A patch _something_ like this.
> >
> > A few notes:
> >
> >  - This is UNTESTED (of course)
> >
> >  - If I did this right, this _only_ overrides the data mode if it's not
> >   explicitly specified on disk in the superblock mount options.
> >
> > IOW, if you have done a
> >
> >        tune2fs -o journal_data_ordered
> >
> > then this will _not_ override that. Only in the absense of any explicit
> > flags should this trigger and then make the choice be 'writeback'.
> >
> > And just to be _extra_ backwards compatible, if you really want the old
> > behavior, and don't want to set the ordering flag explicitly, just answer
> > 'y' to the EXT3_DEFAULTS_TO_ORDERED Kconfig question.
> >
> > What do people think? Anybody want to test?
> >
> >                Linus
> >
> > ---
> >  fs/ext3/Kconfig |   19 +++++++++++++++++++
> >  fs/ext3/super.c |    8 +++++++-
> >  2 files changed, 26 insertions(+), 1 deletions(-)
> >
> > diff --git a/fs/ext3/Kconfig b/fs/ext3/Kconfig
> > index 8e0cfe4..fb3c1a2 100644
> > --- a/fs/ext3/Kconfig
> > +++ b/fs/ext3/Kconfig
> > @@ -28,6 +28,25 @@ config EXT3_FS
> >          To compile this file system support as a module, choose M here: the
> >          module will be called ext3.
> >
> > +config EXT3_DEFAULTS_TO_ORDERED
> > +       bool "Default to 'data=ordered' in ext3 (legacy option)"
> > +       depends on EXT3_FS
> > +       help
> > +         If a filesystem does not explicitly specify a data ordering
> > +         mode, and the journal capability allowed it, ext3 used to
> > +         historically default to 'data=ordered'.
> > +
> > +         That was a rather unfortunate choice, because it leads to all
> > +         kinds of latency problems, and the 'data=writeback' mode is more
> > +         appropriate these days.
> > +
> > +         You should probably always answer 'n' here, and if you really
>             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > +         want to use 'data=ordered' mode, set it in the filesystem itself
> > +         with 'tune2fs -o journal_data_ordered'.
> > +
> > +         But if you really want to enable the legacy default, you can do
> > +         so by answering 'y' to this question.
> > +
> 
> So `allmodconfig' will enable it? Is that the right thing to do, 
> or should it be inverted?
> 
> Gr{oetje,eeting}s,

allmod/allyes will enable all sorts of legacy options.

Since besides myself i'm not aware of any other person on this 
planet actually _booting_ allyes/allmod Linux kernels, i guess this 
is not a big issue anyway :-)

One small detail only: i'd suggest to name it 
CONFIG_COMPAT_EXT3_DEFAULTS_TO_ORDERED, to move it more in line with 
all the CONFIG_COMPAT_* legacy options.

	Ingo
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