On Sun, Mar 08, 2015 at 11:35:59AM -0700, Linus Torvalds wrote:

On Sun, Mar 8, 2015 at 3:02 AM, Ingo Molnar [off-list ref] wrote:
But:

quoted

As a second hack (not to be applied), could we change:

 #define _PAGE_BIT_PROTNONE      _PAGE_BIT_GLOBAL

to:

 #define _PAGE_BIT_PROTNONE      (_PAGE_BIT_GLOBAL+1)

to double check that the position of the bit does not matter?

Agreed. We should definitely try that.

Dave?

As Mel has already mentioned, I'm in Boston for LSFMM and don't have
access to the test rig I've used to generate this.

Also, is there some sane way for me to actually see this behavior on a
regular machine with just a single socket? Dave is apparently running
in some fake-numa setup, I'm wondering if this is easy enough to
reproduce that I could see it myself.

Should be - I don't actually use 500TB of storage to generate this -
50GB on an SSD is all you need from the storage side. I just use a
sparse backing file to make it look like a 500TB device. :P

i.e. create an XFS filesystem on a 500TB sparse file with "mkfs.xfs
-d size=500t,file=1 /path/to/file.img", mount it on loopback or as a
virtio,cache=none device for the guest vm and then use fsmark to
generate several million files spread across many, many directories
such as:

$  fs_mark -D 10000 -S0 -n 100000 -s 1 -L 32 -d \
/mnt/scratch/0 -d /mnt/scratch/1 -d /mnt/scratch/2 -d \
/mnt/scratch/3 -d /mnt/scratch/4 -d /mnt/scratch/5 -d \
/mnt/scratch/6 -d /mnt/scratch/7

That should only take a few minutes to run - if you throw 8p at it
then it should run at >100k files/s being created.

Then unmount and run "xfs_repair -o bhash=101703 /path/to/file.img"
on the resultant image file.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com