Re: 2.6.4-rc1-mm1: queue-congestion-dm-implementation patch

[Miquel van Smoorenburg]

On Tue, 02 Mar 2004 23:21:34, Andrew Morton wrote:
> Kevin Corry <kevcorry@xxxxxxxxxx> wrote:
> >
> > > Changing down_read() in dm_any_congested to down_read_trylock() would
> > > probably fix it for bdi_*_congested(). If you can tell me how to
> > > reproduce it I can try a few things..
> > 
> > Switching to down_read_trylock() would certainly eliminate this problem, as 
> > long as you don't *need* to check the congestion of the underlying devices 
> > each time dm_any_congested() is called.
> 
> It's clear from the trace: we're doing down_read() inside
> sync_sb_inodes()'s inode_lock.
> 
> Yes, a trylock would fix it up, but it's a bit sleazy.
>
> So for two reasons now, it's looking like that semaphore which protects the
> devicemapper tables needs to become a spinlock.  One which has interesting
> ranking properties.

Is that 2.6 material? If so, good. If not, the "passing up" congestion
method doesn't seem so bad after all, I think. At least it keeps the
backing_dev_info struct completely static ..

(I haven't tried 2.6.4-rc1-mm1 yet - the e1000 driver doesn't work for me
 in that kernel, so I can't reach the damn boxes).

Mike.
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