Re: [patch] fs: improved handling of page and buffer IO errors

[Dave Chinner <david@fromorbit.com>]

On Thu, Oct 23, 2008 at 01:15:00PM +0200, Nick Piggin wrote:
> On Thu, Oct 23, 2008 at 10:44:16AM +0100, steve@chygwyn.com wrote:
> > Hi,
> > 
> > On Thu, Oct 23, 2008 at 09:07:11AM +0200, Nick Piggin wrote:
> > > On Thu, Oct 23, 2008 at 10:07:15AM +1100, Dave Chinner wrote:
> > [snip]
> > > 
> > > > You could do the same thing for metadata read operations. e.g. build
> > > > a large directory structure, then do read operations on it (readdir,
> > > > stat, etc) and inject errors into each of those. All filesystems
> > > > should return the (EIO) error to the application in this case.
> > > > 
> > > > Those two cases should be pretty generic and deterministic - they
> > > > both avoid the difficult problem of determining what the response
> > > > to an I/O error during metadata modifcation should be....
> > > 
> > > Good suggestion.
> > > 
> > > I'll see what I can do. I'm using the fault injection stuff, which I
> > > don't think can distinguish metadata, so I might just have to work
> > > out a bio flag or something we can send down to the block layer to
> > > distinguish.
> > > 
> > > Thanks,
> > > Nick
> > >
> > 
> > Don't we already have such a flag? I know that its not set in all
> > the correct places in GFS2 so far, but I've gradually been fixing
> > them to include BIO_RW_META where appropriate.
>  
> That should probably work. It seems to be very incomplete (GFS2
> being one of the few exceptions). Though adding more support in
> ext2 and buffer layer should be enough for me to start with,
> and shouldn't be too hard.

I've posted patches to tag XFS metadata with BIO_RW_META in the
past, but that patch set had performance implications for different I/O
schedulers so it never went further than just a patch. If I
leave all the BIO_RW_SYNC tagging for the metadata bios, then
a single line change to add BIO_RW_META should not have any
performance impact....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com