Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?

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Mark Lord wrote:
Mark Lord wrote:
Andrew Morton wrote:
On Thu, 13 Dec 2007 17:15:06 -0500
James Bottomley <[email protected]> wrote:

On Thu, 2007-12-13 at 14:02 -0800, Andrew Morton wrote:
On Thu, 13 Dec 2007 21:09:59 +0100
Jens Axboe <[email protected]> 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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