Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?

[Mark Lord <liml@rtr.ca>]

Mark Lord wrote:
> Mark Lord wrote:
> > Andrew Morton wrote:
> > > On Thu, 13 Dec 2007 17:15:06 -0500
> > > James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> > >
> > > > On Thu, 2007-12-13 at 14:02 -0800, Andrew Morton wrote:
> > > > > On Thu, 13 Dec 2007 21:09:59 +0100
> > > > > Jens Axboe <jens.axboe@oracle.com> wrote:
> > > > >
> > > > > > OK, it's a vm issue,
> > > > > cc linux-mm and probable culprit.
> > > > >
> > > > > >  I have tens of thousand "backward" pages after a
> > > > > > boot - IOW, bvec->bv_page is the page before bvprv->bv_page, not
> > > > > > reverse. So it looks like that bug got reintroduced.
> > > > > Bill Irwin fixed this a couple of years back: changed the page 
> > > > > allocator so
> > > > > that it mostly hands out pages in ascending physical-address order.
> > > > >
> > > > > I guess we broke that, quite possibly in Mel's page allocator rework.
> > > > >
> > > > > It would help if you could provide us with a simple recipe for
> > > > > demonstrating this problem, please.
> > > > The simple way seems to be to malloc a large area, touch every page and
> > > > then look at the physical pages assigned ... they now mostly seem to be
> > > > descending in physical address.
> > >
> > > OIC.  -mm's /proc/pid/pagemap can be used to get the pfn's...
> > ..
> >
> > I'm actually running the treadmill right now (have been for many 
> > hours, actually,
> > to bisect it to a specific commit.
> >
> > Thought I was almost done, and then noticed that git-bisect doesn't keep
> > the Makefile VERSION lines the same, so I was actually running the wrong
> > kernel after the first few times.. duh.
> >
> > Wrote a script to fix it now.
> ..
>
> Well, that was a waste of three hours.
..

Ahh.. it seems to be sensitive to one/both of these:

CONFIG_HIGHMEM64G=y with 4GB RAM:  not so bad, frequently does 20KB - 48KB segments.
CONFIG_HIGHMEM4G=y  with 2GB RAM:  very severe, rarely does more than 8KB segments.
CONFIG_HIGHMEM4G=y  with 3GB RAM:  very severe, rarely does more than 8KB segments.

So if you want to reproduce this on a large memory machine, use "mem=2GB" for starters.

Still testing..



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