41 строка
2.0 KiB
ReStructuredText
41 строка
2.0 KiB
ReStructuredText
|
.. _free_page_reporting:
|
||
|
|
|
||
|
|
=====================
|
||
|
|
Free Page Reporting
|
||
|
|
=====================
|
||
|
|
|
||
|
|
Free page reporting is an API by which a device can register to receive
|
||
|
|
lists of pages that are currently unused by the system. This is useful in
|
||
|
|
the case of virtualization where a guest is then able to use this data to
|
||
|
|
notify the hypervisor that it is no longer using certain pages in memory.
|
||
|
|
|
||
|
|
For the driver, typically a balloon driver, to use of this functionality
|
||
|
|
it will allocate and initialize a page_reporting_dev_info structure. The
|
||
|
|
field within the structure it will populate is the "report" function
|
||
|
|
pointer used to process the scatterlist. It must also guarantee that it can
|
||
|
|
handle at least PAGE_REPORTING_CAPACITY worth of scatterlist entries per
|
||
|
|
call to the function. A call to page_reporting_register will register the
|
||
|
|
page reporting interface with the reporting framework assuming no other
|
||
|
|
page reporting devices are already registered.
|
||
|
|
|
||
|
|
Once registered the page reporting API will begin reporting batches of
|
||
|
|
pages to the driver. The API will start reporting pages 2 seconds after
|
||
|
|
the interface is registered and will continue to do so 2 seconds after any
|
||
|
|
page of a sufficiently high order is freed.
|
||
|
|
|
||
|
|
Pages reported will be stored in the scatterlist passed to the reporting
|
||
|
|
function with the final entry having the end bit set in entry nent - 1.
|
||
|
|
While pages are being processed by the report function they will not be
|
||
|
|
accessible to the allocator. Once the report function has been completed
|
||
|
|
the pages will be returned to the free area from which they were obtained.
|
||
|
|
|
||
|
|
Prior to removing a driver that is making use of free page reporting it
|
||
|
|
is necessary to call page_reporting_unregister to have the
|
||
|
|
page_reporting_dev_info structure that is currently in use by free page
|
||
|
|
reporting removed. Doing this will prevent further reports from being
|
||
|
|
issued via the interface. If another driver or the same driver is
|
||
|
|
registered it is possible for it to resume where the previous driver had
|
||
|
|
left off in terms of reporting free pages.
|
||
|
|
|
||
|
|
Alexander Duyck, Dec 04, 2019
|