docs/vm: page_migration: convert to ReST format

Signed-off-by: NMike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/vm/page_migration

+.. _page_migration:
+
+==============
 Page migration
---------------
+==============
 
 Page migration allows the moving of the physical location of pages between
 nodes in a numa system while the process is running. This means that the
@@ -20,7 +23,7 @@ Page migration functions are provided by the numactl package by Andi Kleen
 (a version later than 0.9.3 is required. Get it from
 ftp://oss.sgi.com/www/projects/libnuma/download/). numactl provides libnuma
 which provides an interface similar to other numa functionality for page
-migration.  cat /proc/<pid>/numa_maps allows an easy review of where the
+migration.  cat ``/proc/<pid>/numa_maps`` allows an easy review of where the
 pages of a process are located. See also the numa_maps documentation in the
 proc(5) man page.
 
@@ -56,8 +59,8 @@ description for those trying to use migrate_pages() from the kernel
 (for userspace usage see the Andi Kleen's numactl package mentioned above)
 and then a low level description of how the low level details work.
 
-A. In kernel use of migrate_pages()
------------------------------------
+In kernel use of migrate_pages()
+================================
 
 1. Remove pages from the LRU.
 
@@ -78,8 +81,8 @@ A. In kernel use of migrate_pages()
    the new page for each page that is considered for
    moving.
 
-B. How migrate_pages() works
-----------------------------
+How migrate_pages() works
+=========================
 
 migrate_pages() does several passes over its list of pages. A page is moved
 if all references to a page are removable at the time. The page has
@@ -142,8 +145,8 @@ Steps:
 20. The new page is moved to the LRU and can be scanned by the swapper
     etc again.
 
-C. Non-LRU page migration
--------------------------
+Non-LRU page migration
+======================
 
 Although original migration aimed for reducing the latency of memory access
 for NUMA, compaction who want to create high-order page is also main customer.
@@ -164,89 +167,91 @@ migration path.
 If a driver want to make own pages movable, it should define three functions
 which are function pointers of struct address_space_operations.
 
-1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);
+1. ``bool (*isolate_page) (struct page *page, isolate_mode_t mode);``
 
-What VM expects on isolate_page function of driver is to return *true*
-if driver isolates page successfully. On returing true, VM marks the page
-as PG_isolated so concurrent isolation in several CPUs skip the page
-for isolation. If a driver cannot isolate the page, it should return *false*.
+   What VM expects on isolate_page function of driver is to return *true*
+   if driver isolates page successfully. On returing true, VM marks the page
+   as PG_isolated so concurrent isolation in several CPUs skip the page
+   for isolation. If a driver cannot isolate the page, it should return *false*.
 
-Once page is successfully isolated, VM uses page.lru fields so driver
-shouldn't expect to preserve values in that fields.
+   Once page is successfully isolated, VM uses page.lru fields so driver
+   shouldn't expect to preserve values in that fields.
 
-2. int (*migratepage) (struct address_space *mapping,
-		struct page *newpage, struct page *oldpage, enum migrate_mode);
+2. ``int (*migratepage) (struct address_space *mapping,``
+|	``struct page *newpage, struct page *oldpage, enum migrate_mode);``
 
-After isolation, VM calls migratepage of driver with isolated page.
-The function of migratepage is to move content of the old page to new page
-and set up fields of struct page newpage. Keep in mind that you should
-indicate to the VM the oldpage is no longer movable via __ClearPageMovable()
-under page_lock if you migrated the oldpage successfully and returns
-MIGRATEPAGE_SUCCESS. If driver cannot migrate the page at the moment, driver
-can return -EAGAIN. On -EAGAIN, VM will retry page migration in a short time
-because VM interprets -EAGAIN as "temporal migration failure". On returning
-any error except -EAGAIN, VM will give up the page migration without retrying
-in this time.
+   After isolation, VM calls migratepage of driver with isolated page.
+   The function of migratepage is to move content of the old page to new page
+   and set up fields of struct page newpage. Keep in mind that you should
+   indicate to the VM the oldpage is no longer movable via __ClearPageMovable()
+   under page_lock if you migrated the oldpage successfully and returns
+   MIGRATEPAGE_SUCCESS. If driver cannot migrate the page at the moment, driver
+   can return -EAGAIN. On -EAGAIN, VM will retry page migration in a short time
+   because VM interprets -EAGAIN as "temporal migration failure". On returning
+   any error except -EAGAIN, VM will give up the page migration without retrying
+   in this time.
 
-Driver shouldn't touch page.lru field VM using in the functions.
+   Driver shouldn't touch page.lru field VM using in the functions.
 
-3. void (*putback_page)(struct page *);
+3. ``void (*putback_page)(struct page *);``
 
-If migration fails on isolated page, VM should return the isolated page
-to the driver so VM calls driver's putback_page with migration failed page.
-In this function, driver should put the isolated page back to the own data
-structure.
+   If migration fails on isolated page, VM should return the isolated page
+   to the driver so VM calls driver's putback_page with migration failed page.
+   In this function, driver should put the isolated page back to the own data
+   structure.
 
 4. non-lru movable page flags
 
-There are two page flags for supporting non-lru movable page.
+   There are two page flags for supporting non-lru movable page.
 
-* PG_movable
+   * PG_movable
 
-Driver should use the below function to make page movable under page_lock.
+     Driver should use the below function to make page movable under page_lock::
 
 	void __SetPageMovable(struct page *page, struct address_space *mapping)
 
-It needs argument of address_space for registering migration family functions
-which will be called by VM. Exactly speaking, PG_movable is not a real flag of
-struct page. Rather than, VM reuses page->mapping's lower bits to represent it.
+     It needs argument of address_space for registering migration
+     family functions which will be called by VM. Exactly speaking,
+     PG_movable is not a real flag of struct page. Rather than, VM
+     reuses page->mapping's lower bits to represent it.
 
+::
 	#define PAGE_MAPPING_MOVABLE 0x2
 	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;
 
-so driver shouldn't access page->mapping directly. Instead, driver should
-use page_mapping which mask off the low two bits of page->mapping under
-page lock so it can get right struct address_space.
-
-For testing of non-lru movable page, VM supports __PageMovable function.
-However, it doesn't guarantee to identify non-lru movable page because
-page->mapping field is unified with other variables in struct page.
-As well, if driver releases the page after isolation by VM, page->mapping
-doesn't have stable value although it has PAGE_MAPPING_MOVABLE
-(Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
-page is LRU or non-lru movable once the page has been isolated. Because
-LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
-good for just peeking to test non-lru movable pages before more expensive
-checking with lock_page in pfn scanning to select victim.
-
-For guaranteeing non-lru movable page, VM provides PageMovable function.
-Unlike __PageMovable, PageMovable functions validates page->mapping and
-mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
-destroying of page->mapping.
-
-Driver using __SetPageMovable should clear the flag via __ClearMovablePage
-under page_lock before the releasing the page.
-
-* PG_isolated
-
-To prevent concurrent isolation among several CPUs, VM marks isolated page
-as PG_isolated under lock_page. So if a CPU encounters PG_isolated non-lru
-movable page, it can skip it. Driver doesn't need to manipulate the flag
-because VM will set/clear it automatically. Keep in mind that if driver
-sees PG_isolated page, it means the page have been isolated by VM so it
-shouldn't touch page.lru field.
-PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
-for own purpose.
+     so driver shouldn't access page->mapping directly. Instead, driver should
+     use page_mapping which mask off the low two bits of page->mapping under
+     page lock so it can get right struct address_space.
+
+     For testing of non-lru movable page, VM supports __PageMovable function.
+     However, it doesn't guarantee to identify non-lru movable page because
+     page->mapping field is unified with other variables in struct page.
+     As well, if driver releases the page after isolation by VM, page->mapping
+     doesn't have stable value although it has PAGE_MAPPING_MOVABLE
+     (Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
+     page is LRU or non-lru movable once the page has been isolated. Because
+     LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
+     good for just peeking to test non-lru movable pages before more expensive
+     checking with lock_page in pfn scanning to select victim.
+
+     For guaranteeing non-lru movable page, VM provides PageMovable function.
+     Unlike __PageMovable, PageMovable functions validates page->mapping and
+     mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
+     destroying of page->mapping.
+
+     Driver using __SetPageMovable should clear the flag via __ClearMovablePage
+     under page_lock before the releasing the page.
+
+   * PG_isolated
+
+     To prevent concurrent isolation among several CPUs, VM marks isolated page
+     as PG_isolated under lock_page. So if a CPU encounters PG_isolated non-lru
+     movable page, it can skip it. Driver doesn't need to manipulate the flag
+     because VM will set/clear it automatically. Keep in mind that if driver
+     sees PG_isolated page, it means the page have been isolated by VM so it
+     shouldn't touch page.lru field.
+     PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
+     for own purpose.
 
 Christoph Lameter, May 8, 2006.
 Minchan Kim, Mar 28, 2016.