diff options
Diffstat (limited to 'Documentation/vm')
| -rw-r--r-- | Documentation/vm/free_page_reporting.rst | 40 | ||||
| -rw-r--r-- | Documentation/vm/zswap.rst | 20 |
2 files changed, 52 insertions, 8 deletions
diff --git a/Documentation/vm/free_page_reporting.rst b/Documentation/vm/free_page_reporting.rst new file mode 100644 index 000000000000..8c05e62d8b2b --- /dev/null +++ b/Documentation/vm/free_page_reporting.rst @@ -0,0 +1,40 @@ +.. _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 diff --git a/Documentation/vm/zswap.rst b/Documentation/vm/zswap.rst index 61f6185188cd..f8c6a79d7c70 100644 --- a/Documentation/vm/zswap.rst +++ b/Documentation/vm/zswap.rst @@ -35,9 +35,11 @@ Zswap evicts pages from compressed cache on an LRU basis to the backing swap device when the compressed pool reaches its size limit. This requirement had been identified in prior community discussions. -Zswap is disabled by default but can be enabled at boot time by setting -the ``enabled`` attribute to 1 at boot time. ie: ``zswap.enabled=1``. Zswap -can also be enabled and disabled at runtime using the sysfs interface. +Whether Zswap is enabled at the boot time depends on whether +the ``CONFIG_ZSWAP_DEFAULT_ON`` Kconfig option is enabled or not. +This setting can then be overridden by providing the kernel command line +``zswap.enabled=`` option, for example ``zswap.enabled=0``. +Zswap can also be enabled and disabled at runtime using the sysfs interface. An example command to enable zswap at runtime, assuming sysfs is mounted at ``/sys``, is:: @@ -64,9 +66,10 @@ allocation in zpool is not directly accessible by address. Rather, a handle is returned by the allocation routine and that handle must be mapped before being accessed. The compressed memory pool grows on demand and shrinks as compressed pages are freed. The pool is not preallocated. By default, a zpool -of type zbud is created, but it can be selected at boot time by -setting the ``zpool`` attribute, e.g. ``zswap.zpool=zbud``. It can -also be changed at runtime using the sysfs ``zpool`` attribute, e.g.:: +of type selected in ``CONFIG_ZSWAP_ZPOOL_DEFAULT`` Kconfig option is created, +but it can be overridden at boot time by setting the ``zpool`` attribute, +e.g. ``zswap.zpool=zbud``. It can also be changed at runtime using the sysfs +``zpool`` attribute, e.g.:: echo zbud > /sys/module/zswap/parameters/zpool @@ -97,8 +100,9 @@ controlled policy: * max_pool_percent - The maximum percentage of memory that the compressed pool can occupy. -The default compressor is lzo, but it can be selected at boot time by -setting the ``compressor`` attribute, e.g. ``zswap.compressor=lzo``. +The default compressor is selected in ``CONFIG_ZSWAP_COMPRESSOR_DEFAULT`` +Kconfig option, but it can be overridden at boot time by setting the +``compressor`` attribute, e.g. ``zswap.compressor=lzo``. It can also be changed at runtime using the sysfs "compressor" attribute, e.g.:: |