[PATCH 18/32] docs/vm: page_migration: convert to ReST format
Mike Rapoport
rppt at linux.vnet.ibm.com
Thu Mar 22 06:22:34 AEDT 2018
Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
---
Documentation/vm/page_migration | 149 +++++++++++++++++++++-------------------
1 file changed, 77 insertions(+), 72 deletions(-)
diff --git a/Documentation/vm/page_migration b/Documentation/vm/page_migration
index 0478ae2..07b67a8 100644
--- a/Documentation/vm/page_migration
+++ b/Documentation/vm/page_migration
@@ -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.
@@ -164,89 +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.
--
2.7.4
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