Re: [patch 0/3] j_state_lock, j_list_lock, remove-bitlocks

[Ingo Molnar]

* Andrew Morton <akpm@xxxxxxxx> wrote:

> >  > There's a little lock ranking diagram in jbd.h which tells us that
> >  > these locks nest inside j_list_lock and j_state_lock.  So I guess
> >  > you'll need to turn those into semaphores.
> > 
> >  indeed. I did this (see the three followup patches, against BK-curr),
> >  and it builds/boots/works just fine on an ext3 box. Do we want to try
> >  this in -mm?
> 
> ooh, I'd rather not.  I spent an intense three days removing all the
> sleeping locks from ext3 (and three months debugging the result). 
> Ended up gaining 1000% on 16-way.
> 
> Putting them back in will really hurt the SMP performance.

seems like turning the bitlocks into spinlocks is the best option then. 
We'd need one lock in buffer_head (j_state_lock, renamed to something
more sensible like b_private_lock), and one lock in journal_head
(j_list_lock) i guess. How much would the +4/+8 bytes size increase in
buffer_head [on SMP] be frowned upon? 

	Ingo
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