Re: [Ext2-devel] Re: [PATCH] 2.6.11-mm3 patch for ext3 writeback"nobh" option

From: Badari Pulavarty
Date: Tue Mar 15 2005 - 11:43:51 EST

On Tue, 2005-03-15 at 08:26, Arjan van de Ven wrote:
> On Tue, 2005-03-15 at 08:09 -0800, Badari Pulavarty wrote:
> > On Mon, 2005-03-14 at 18:09, Andrew Morton wrote:
> > > Badari Pulavarty <pbadari@xxxxxxxxxx> wrote:
> > > >
> > > > Here is the 2.6.11-mm3 version of patch for adding "nobh"
> > > > support for ext3 writeback mode.
> > >
> > > Care to update Documentation/filesystems/ext3.txt?
> >
> > Yes. I will do that. I am planning to add "nobh" support to
> > ext3 ordered mode also, since its the default one. We need
> > to modify generic interfaces like mpage_writepage(s) to
> > keep track of bio count and make journal code wait for them etc. -
> > at that point the "generic" code will no longer be generic.
> > I am thinking of a way to do it *less* intrusively.
> >
> > At that point, we can make "nobh" default option. (which
> > needs less documentation).
> I still don't get why you want a mount option. Sure during development
> it can be nice.. but do you still want it in the production trees??

Once I get "nobh" working for both ordered and writeback mode -
I will take out the option. Only reason why, you may
want "bh"s are for faster lookups. "bh" stores the get_block()
information, getting rid of it means - we need to do few more
get_block() calls when we need the disk mapping.

We have seen small amount of "reads" when we are doing write-only
tests with "nobh" option. I am not at a point, where I can quantify
the performance hit due to not caching the disk mapping info.


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