Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?

[Mark Lord <liml@rtr.ca>]

Jens Axboe wrote:
> On Thu, Dec 13 2007, Mark Lord wrote:
> > Matthew Wilcox wrote:
> > > On Thu, Dec 13, 2007 at 01:48:18PM -0500, Mark Lord wrote:
> > > > Problem confirmed.  2.6.23.8 regularly generates segments up to 64KB for 
> > > > libata,
> > > > but 2.6.24 uses only 4KB segments and a *few* 8KB segments.
> > > Just a suspicion ... could this be slab vs slub?  ie check your configs
> > > are the same / similar between the two kernels.
> > ..
> >
> > Mmmm.. a good thought, that one.
> > But I just rechecked, and both have CONFIG_SLAB=y
> >
> > My guess is that something got changed around when Jens
> > reworked the block layer for 2.6.24.
> > I'm going to dig around in there now.
>
> I didn't rework the block layer for 2.6.24 :-). The core block layer
> changes since 2.6.23 are:
>
> - Support for empty barriers. Not a likely candidate.
> - Shared tag queue fixes. Totally unlikely.
> - sg chaining support. Not likely.
> - The bio changes from Neil. Of the bunch, the most likely suspects in
>   this area, since it changes some of the code involved with merges and
>   blk_rq_map_sg().
> - Lots of simple stuff, again very unlikely.
>
> Anyway, it sounds odd for this to be a block layer problem if you do see
> occasional segments being merged. So it sounds more like the input data
> having changed.
>
> Why not just bisect it?
..

Because the early 2.6.24 series failed to boot on this machine
due to bugs in the block layer -- so the code that caused this regression
is probably in the stuff from before the kernels became usable here.

Cheers

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