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>hifive-unleashed-5.1
Mike Rapoport
Jonathan Corbet
parent
25c3bf8aaf
commit
1b7599b5de
|
|
@ -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.
|
||||
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 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.
|
||||
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.
|
||||
Driver using __SetPageMovable should clear the flag via __ClearMovablePage
|
||||
under page_lock before the releasing the page.
|
||||
|
||||
* PG_isolated
|
||||
* 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.
|
||||
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.
|
||||
|
|
|
|||
Loading…
Reference in New Issue