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Date: Fri, 03 Jan 2020 13:17:10 -0800 From: Alexander Duyck <alexander.duyck@...il.com> To: kvm@...r.kernel.org, mst@...hat.com, linux-kernel@...r.kernel.org, willy@...radead.org, mhocko@...nel.org, linux-mm@...ck.org, akpm@...ux-foundation.org, mgorman@...hsingularity.net, vbabka@...e.cz Cc: yang.zhang.wz@...il.com, nitesh@...hat.com, konrad.wilk@...cle.com, david@...hat.com, pagupta@...hat.com, riel@...riel.com, lcapitulino@...hat.com, dave.hansen@...el.com, wei.w.wang@...el.com, aarcange@...hat.com, pbonzini@...hat.com, dan.j.williams@...el.com, alexander.h.duyck@...ux.intel.com, osalvador@...e.de Subject: [PATCH v16 9/9] mm: Add free page reporting documentation From: Alexander Duyck <alexander.h.duyck@...ux.intel.com> 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@...ux.intel.com> --- Documentation/vm/free_page_reporting.rst | 41 ++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) create mode 100644 Documentation/vm/free_page_reporting.rst diff --git a/Documentation/vm/free_page_reporting.rst b/Documentation/vm/free_page_reporting.rst new file mode 100644 index 000000000000..33f54a450a4a --- /dev/null +++ b/Documentation/vm/free_page_reporting.rst @@ -0,0 +1,41 @@ +.. _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 +
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