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>
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@ -1,5 +1,8 @@
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.. _page_migration:
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==============
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Page migration
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--------------
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==============
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Page migration allows the moving of the physical location of pages between
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nodes in a numa system while the process is running. This means that the
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@ -20,7 +23,7 @@ Page migration functions are provided by the numactl package by Andi Kleen
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(a version later than 0.9.3 is required. Get it from
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ftp://oss.sgi.com/www/projects/libnuma/download/). numactl provides libnuma
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which provides an interface similar to other numa functionality for page
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migration. cat /proc/<pid>/numa_maps allows an easy review of where the
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migration. cat ``/proc/<pid>/numa_maps`` allows an easy review of where the
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pages of a process are located. See also the numa_maps documentation in the
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proc(5) man page.
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@ -56,8 +59,8 @@ description for those trying to use migrate_pages() from the kernel
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(for userspace usage see the Andi Kleen's numactl package mentioned above)
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and then a low level description of how the low level details work.
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A. In kernel use of migrate_pages()
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-----------------------------------
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In kernel use of migrate_pages()
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================================
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1. Remove pages from the LRU.
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@ -78,8 +81,8 @@ A. In kernel use of migrate_pages()
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the new page for each page that is considered for
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moving.
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B. How migrate_pages() works
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----------------------------
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How migrate_pages() works
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=========================
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migrate_pages() does several passes over its list of pages. A page is moved
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if all references to a page are removable at the time. The page has
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@ -142,8 +145,8 @@ Steps:
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20. The new page is moved to the LRU and can be scanned by the swapper
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etc again.
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C. Non-LRU page migration
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-------------------------
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Non-LRU page migration
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======================
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Although original migration aimed for reducing the latency of memory access
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for NUMA, compaction who want to create high-order page is also main customer.
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@ -164,7 +167,7 @@ migration path.
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If a driver want to make own pages movable, it should define three functions
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which are function pointers of struct address_space_operations.
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1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);
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1. ``bool (*isolate_page) (struct page *page, isolate_mode_t mode);``
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What VM expects on isolate_page function of driver is to return *true*
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if driver isolates page successfully. On returing true, VM marks the page
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@ -174,8 +177,8 @@ for isolation. If a driver cannot isolate the page, it should return *false*.
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Once page is successfully isolated, VM uses page.lru fields so driver
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shouldn't expect to preserve values in that fields.
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2. int (*migratepage) (struct address_space *mapping,
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struct page *newpage, struct page *oldpage, enum migrate_mode);
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2. ``int (*migratepage) (struct address_space *mapping,``
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| ``struct page *newpage, struct page *oldpage, enum migrate_mode);``
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After isolation, VM calls migratepage of driver with isolated page.
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The function of migratepage is to move content of the old page to new page
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@ -190,7 +193,7 @@ in this time.
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Driver shouldn't touch page.lru field VM using in the functions.
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3. void (*putback_page)(struct page *);
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3. ``void (*putback_page)(struct page *);``
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If migration fails on isolated page, VM should return the isolated page
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to the driver so VM calls driver's putback_page with migration failed page.
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@ -203,14 +206,16 @@ There are two page flags for supporting non-lru movable page.
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* PG_movable
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Driver should use the below function to make page movable under page_lock.
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Driver should use the below function to make page movable under page_lock::
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void __SetPageMovable(struct page *page, struct address_space *mapping)
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It needs argument of address_space for registering migration family functions
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which will be called by VM. Exactly speaking, PG_movable is not a real flag of
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struct page. Rather than, VM reuses page->mapping's lower bits to represent it.
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It needs argument of address_space for registering migration
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family functions which will be called by VM. Exactly speaking,
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PG_movable is not a real flag of struct page. Rather than, VM
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reuses page->mapping's lower bits to represent it.
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::
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#define PAGE_MAPPING_MOVABLE 0x2
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page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;
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