Re: per BDI dirty limit (was Re: -mm merge plans for 2.6.24)

[Peter Zijlstra <peterz@infradead.org>]

On Tue, 2007-10-02 at 01:31 -0700, Andrew Morton wrote:
> On Tue, 02 Oct 2007 10:17:05 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Mon, 2007-10-01 at 14:22 -0700, Andrew Morton wrote:
> > 
> > > nfs-remove-congestion_end.patch
> > > lib-percpu_counter_add.patch
> > > lib-percpu_counter_sub.patch
> > > lib-percpu_counter-variable-batch.patch
> > > lib-make-percpu_counter_add-take-s64.patch
> > > lib-percpu_counter_set.patch
> > > lib-percpu_counter_sum_positive.patch
> > > lib-percpu_count_sum.patch
> > > lib-percpu_counter_init-error-handling.patch
> > > lib-percpu_counter_init_irq.patch
> > > mm-bdi-init-hooks.patch
> > > mm-scalable-bdi-statistics-counters.patch
> > > mm-count-reclaimable-pages-per-bdi.patch
> > > mm-count-writeback-pages-per-bdi.patch
> > 
> > This one:
> > > mm-expose-bdi-statistics-in-sysfs.patch
> > 
> > > lib-floating-proportions.patch
> > > mm-per-device-dirty-threshold.patch
> > > mm-per-device-dirty-threshold-warning-fix.patch
> > > mm-per-device-dirty-threshold-fix.patch
> > > mm-dirty-balancing-for-tasks.patch
> > > mm-dirty-balancing-for-tasks-warning-fix.patch
> > 
> > And, this one:
> > > debug-sysfs-files-for-the-current-ratio-size-total.patch
> > 
> > 
> > I'm not sure polluting /sys/block/<foo>/queue/ like that is The Right
> > Thing.
> 
> hm, I suppose not.  It leaves nowhere for nfs, for a start.
> 
> > These patches sure were handy when debugging this, but not sure
> > they want to move to maineline.
> > 
> > Maybe we want /sys/bdi/<foo>/ or maybe /debug/bdi/<foo>/
> > 
> 
> If you think we'll need this stuff for support/debug during 2.6.24-rcX then
> sure - we can always take it out prior to 2.6.24-final.
> 
> otoh, if we're going to take that approach we might as well leave things in
> /sys/block/<foo>/queue.

People seem to have tested the code in various demanding scenarios (both
-mm and the back-port to .22), so I'm fairly confident that this part
works well (famous last words,.. I know I'll regret having said this).

Also the NFS issue bothers me to no end.

I'll try and come up with a /sys/bdi/<foo> thing. SLUB should have some
sysfs code I can copy from - last time I looked at doing sysfs I just
gave up. God awful mess that is.