![Alexander Duyck](/assets/img/avatar_default.png)
Add documentation for free page reporting. Currently the only consumer is virtio-balloon, however it is possible that other drivers might make use of this so it is best to add a bit of documetation explaining at a high level how to use the API. Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Luiz Capitulino <lcapitulino@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Nitesh Narayan Lal <nitesh@redhat.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Pankaj Gupta <pagupta@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Wei Wang <wei.w.wang@intel.com> Cc: Yang Zhang <yang.zhang.wz@gmail.com> Cc: wei qi <weiqi4@huawei.com> Link: http://lkml.kernel.org/r/20200211224730.29318.43815.stgit@localhost.localdomain Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
41 lines
2 KiB
ReStructuredText
41 lines
2 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
|