Re: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for _PAGE_NUMA v2

["H. Peter Anvin" <hpa@zytor.com>]

On 04/08/2014 06:09 AM, Mel Gorman wrote:
> Using unused physical bits is something that will break eventually.
> 
> Changelog since V1
> o Reuse software-bits
> o Use paravirt ops when modifying PTEs in the NUMA helpers
> 
> Aliasing _PAGE_NUMA and _PAGE_PROTNONE had some convenient properties but
> it ultimately gave Xen a headache and pisses almost everybody off that
> looks closely at it. Two discussions on "why this makes sense" is one
> discussion too many so rather than having a third so here is this series.
> This series reuses the PTE bits that are available to the programmer.
> This adds some contraints on how and when automatic NUMA balancing can be
> enabled but it should go away again when Xen stops using _PAGE_IOMAP.
> 
> The series also converts the NUMA helpers to use paravirt-friendly operations
> but it needs a Tested-by from the Xen and powerpc people.
> 

It is proably simpler to just base this patchset on top of David
Vrabel's which actually *does* remove _PAGE_IOMAP.

David, is your patchset going to be pushed in this merge window as expected?

That being said, these bits are precious, and if this ends up being a
case where "only Xen needs another bit" once again then Xen should
expect to get kicked to the curb at a moment's notice.

	-hpa


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