On Fri, Jan 15, 2016 at 11:41:50AM -0800, Darrick J. Wong wrote:

On Fri, Jan 08, 2016 at 02:49:44PM -0500, Matthew Wilcox wrote:

quoted

From: Matthew Wilcox <redacted>

Andrew, I think this is ready for a spin in -mm.

v3: Rebased against current mmtom
v2: Reduced churn in filesystems by switching to ->huge_fault interface
    Addressed concerns from Kirill

We have customer demand to use 1GB pages to map DAX files.  Unlike the 2MB
page support, the Linux MM does not currently support PUD pages, so I have
attempted to add support for the necessary pieces for DAX huge PUD pages.

Filesystems still need work to allocate 1GB pages.  With ext4, I can
only get 16MB of contiguous space, although it is aligned.  With XFS,
I can get 80MB less than 1GB, and it's not aligned.  The XFS problem
may be due to the small amount of RAM in my test machine.

"It's not aligned"... I don't know the details of what you're trying to do, but
are you trying to create a file where each GB of logical address space maps to
a contiguous GB of physical space, and both logical and physical offsets align
to a 1GB boundary?

If the XFS is formatted with stripe unit/width of 1G, an extent size hint of 1G
is put on the file, and the whole file is allocated in 1G chunks, I think
you're supposed to be able to make the above happen:

If you really, really want to guarantee 1GB aligned extents for file
data on XFS, use the realtime device with a 1GB extent size.....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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