Re: [PATCH resend^2] mm: increase RECLAIM_DISTANCE to 30

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 11 Apr 2011 19:27:21 -0700
Dave Hansen <dave@linux.vnet.ibm.com> wrote:

> On Tue, 2011-04-12 at 10:01 +0900, KOSAKI Motohiro wrote:
> > > On Mon, 2011-04-11 at 17:19 +0900, KOSAKI Motohiro wrote:
> > > > This patch raise zone_reclaim_mode threshold to 30. 30 don't have
> > > > specific meaning. but 20 mean one-hop QPI/Hypertransport and such
> > > > relatively cheap 2-4 socket machine are often used for tradiotional
> > > > server as above. The intention is, their machine don't use
> > > > zone_reclaim_mode.
> > > 
> > > I know specifically of pieces of x86 hardware that set the information
> > > in the BIOS to '21' *specifically* so they'll get the zone_reclaim_mode
> > > behavior which that implies.
> > 
> > Which hardware?
> 
> I'd have to go digging for the model numbers.  I just remember having
> discussions with folks about it a couple of years ago.  My memory isn't
> what it used to be. :)
> 
> > The reason why now we decided to change default is the original bug reporter was using
> > mere commodity whitebox hardware and very common workload. 
> > If it is enough commotidy, we have to concern it. but if it is special, we don't care it.
> > Hardware vendor should fix a firmware.
> 
> Yeah, it's certainly a "simple" fix.  The distance tables can certainly
> be adjusted easily, and worked around pretty trivially with boot
> options.  If we decide to change the generic case, let's also make sure
> that we put something else in place simultaneously that is nice for the
> folks that don't want it changed.  Maybe something DMI-based that digs
> for model numbers?
> 
> I'll go try and dig for some more specifics on the hardware so we at
> least have something to test on.
> 

How's that digging coming along?

I'm pretty wobbly about this patch.  Perhaps we should set
RECLAIM_DISTANCE to pi/2 or something, to force people to correctly set
the dang thing in initscripts.