In some scenarios Hyper-V needs to manage memory more tightly, so it needs as
much information as possible about unused guest pages. To that end Hyper-V
now allows free page reporting in chunks smaller than 2 Mbytes. Because of
the performance tradeoffs, we want to make the chunk size configurable. Since
there's already a free page reporting module parameter, let's use that rather
than creating yet another parameter.

Configurable order free page reporting is enabled in page_reporting
driver in mm tree. However, changes need to be made in drivers like
hyper-v's hv_balloon to make it aware of the page order.
These patches add support for the same.
In the page_reporting driver(patch 1) we export the page_reporting_order
module parameter. Besides this, in the page_reporting module a check is
added to ensure that whenever the page_reporting_order value is changed, it
is within the prescribed limits.

The hv_balloon side changes(patch 2) include consuming the exported
page_reporting_order. Making changes in reporting these variable order
free pages as cold discard hints to hyper-v and dropping and refining
checks that restrict the order to a minimum of 9(default).

---
Changes in v2
  * Add more details in the cover letter about the motivation
  * Fix the threading between dependent patches

Shradha Gupta (2):
  mm/page_reporting: Add checks for page_reporting_order param
  hv_balloon: Add support for configurable order free page reporting

 drivers/hv/hv_balloon.c | 94 ++++++++++++++++++++++++++++++++---------
 mm/page_reporting.c     | 50 +++++++++++++++++++---
 2 files changed, 118 insertions(+), 26 deletions(-)

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2.37.2