docs/vm: page_migration: convert to ReST format

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mike Rapoport 2018-03-21 21:22:34 +02:00 committed by Jonathan Corbet
parent 25c3bf8aaf
commit 1b7599b5de
1 changed files with 72 additions and 67 deletions

View File

@ -1,5 +1,8 @@
.. _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.
@ -164,7 +167,7 @@ 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
@ -174,8 +177,8 @@ 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.
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
@ -190,7 +193,7 @@ in this time.
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.
@ -203,14 +206,16 @@ There are two page flags for supporting non-lru movable page.
* 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;