On 05/07/2022 13:47, Jan Beulich wrote:
Page tables are used for two purposes after allocation: They either
start out all empty, or they are filled to replace a superpage.
Subsequently, to replace all empty or fully contiguous page tables,
contiguous sub-regions will be recorded within individual page tables.
Install the initial set of markers immediately after allocation. Make
sure to retain these markers when further populating a page table in
preparation for it to replace a superpage.
The markers are simply 4-bit fields holding the order value of
contiguous entries. To demonstrate this, if a page table had just 16
entries, this would be the initial (fully contiguous) set of markers:
index 0 1 2 3 4 5 6 7 8 9 A B C D E F
marker 4 0 1 0 2 0 1 0 3 0 1 0 2 0 1 0
"Contiguous" here means not only present entries with successively
increasing MFNs, each one suitably aligned for its slot, and identical
attributes, but also a respective number of all non-present (zero except
for the markers) entries.
Signed-off-by: Jan Beulich <jbeul...@suse.com>
Reviewed-by: Kevin Tian <kevin.t...@intel.com>
Reviewed-by: Roger Pau Monné <roger....@citrix.com>
Reviewed-by: Paul Durrant <p...@xen.org>
