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-rw-r--r--Documentation/vm/page_migration29
1 files changed, 13 insertions, 16 deletions
diff --git a/Documentation/vm/page_migration b/Documentation/vm/page_migration
index 0a5d5fb18854..99f89aa10169 100644
--- a/Documentation/vm/page_migration
+++ b/Documentation/vm/page_migration
@@ -26,8 +26,13 @@ a process are located. See also the numa_maps manpage in the numactl package.
26Manual migration is useful if for example the scheduler has relocated 26Manual migration is useful if for example the scheduler has relocated
27a process to a processor on a distant node. A batch scheduler or an 27a process to a processor on a distant node. A batch scheduler or an
28administrator may detect the situation and move the pages of the process 28administrator may detect the situation and move the pages of the process
29nearer to the new processor. At some point in the future we may have 29nearer to the new processor. The kernel itself does only provide
30some mechanism in the scheduler that will automatically move the pages. 30manual page migration support. Automatic page migration may be implemented
31through user space processes that move pages. A special function call
32"move_pages" allows the moving of individual pages within a process.
33A NUMA profiler may f.e. obtain a log showing frequent off node
34accesses and may use the result to move pages to more advantageous
35locations.
31 36
32Larger installations usually partition the system using cpusets into 37Larger installations usually partition the system using cpusets into
33sections of nodes. Paul Jackson has equipped cpusets with the ability to 38sections of nodes. Paul Jackson has equipped cpusets with the ability to
@@ -62,22 +67,14 @@ A. In kernel use of migrate_pages()
62 It also prevents the swapper or other scans to encounter 67 It also prevents the swapper or other scans to encounter
63 the page. 68 the page.
64 69
652. Generate a list of newly allocates pages. These pages will contain the 702. We need to have a function of type new_page_t that can be
66 contents of the pages from the first list after page migration is 71 passed to migrate_pages(). This function should figure out
67 complete. 72 how to allocate the correct new page given the old page.
68 73
693. The migrate_pages() function is called which attempts 743. The migrate_pages() function is called which attempts
70 to do the migration. It returns the moved pages in the 75 to do the migration. It will call the function to allocate
71 list specified as the third parameter and the failed 76 the new page for each page that is considered for
72 migrations in the fourth parameter. When the function 77 moving.
73 returns the first list will contain the pages that could still be retried.
74
754. The leftover pages of various types are returned
76 to the LRU using putback_to_lru_pages() or otherwise
77 disposed of. The pages will still have the refcount as
78 increased by isolate_lru_pages() if putback_to_lru_pages() is not
79 used! The kernel may want to handle the various cases of failures in
80 different ways.
81 78
82B. How migrate_pages() works 79B. How migrate_pages() works
83---------------------------- 80----------------------------