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authorChristoph Lameter <clameter@sgi.com>2006-06-23 05:03:55 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-23 10:42:53 -0400
commit742755a1d8ce2b548428f7aacf1758b4bba50080 (patch)
tree53426657e14dc19a694d418274c9a6f4dcb8a997 /Documentation
parent95a402c3847cc16f4ba03013cd01404fa0f14c2e (diff)
[PATCH] page migration: sys_move_pages(): support moving of individual pages
move_pages() is used to move individual pages of a process. The function can be used to determine the location of pages and to move them onto the desired node. move_pages() returns status information for each page. long move_pages(pid, number_of_pages_to_move, addresses_of_pages[], nodes[] or NULL, status[], flags); The addresses of pages is an array of void * pointing to the pages to be moved. The nodes array contains the node numbers that the pages should be moved to. If a NULL is passed instead of an array then no pages are moved but the status array is updated. The status request may be used to determine the page state before issuing another move_pages() to move pages. The status array will contain the state of all individual page migration attempts when the function terminates. The status array is only valid if move_pages() completed successfullly. Possible page states in status[]: 0..MAX_NUMNODES The page is now on the indicated node. -ENOENT Page is not present -EACCES Page is mapped by multiple processes and can only be moved if MPOL_MF_MOVE_ALL is specified. -EPERM The page has been mlocked by a process/driver and cannot be moved. -EBUSY Page is busy and cannot be moved. Try again later. -EFAULT Invalid address (no VMA or zero page). -ENOMEM Unable to allocate memory on target node. -EIO Unable to write back page. The page must be written back in order to move it since the page is dirty and the filesystem does not provide a migration function that would allow the moving of dirty pages. -EINVAL A dirty page cannot be moved. The filesystem does not provide a migration function and has no ability to write back pages. The flags parameter indicates what types of pages to move: MPOL_MF_MOVE Move pages that are only mapped by the process. MPOL_MF_MOVE_ALL Also move pages that are mapped by multiple processes. Requires sufficient capabilities. Possible return codes from move_pages() -ENOENT No pages found that would require moving. All pages are either already on the target node, not present, had an invalid address or could not be moved because they were mapped by multiple processes. -EINVAL Flags other than MPOL_MF_MOVE(_ALL) specified or an attempt to migrate pages in a kernel thread. -EPERM MPOL_MF_MOVE_ALL specified without sufficient priviledges. or an attempt to move a process belonging to another user. -EACCES One of the target nodes is not allowed by the current cpuset. -ENODEV One of the target nodes is not online. -ESRCH Process does not exist. -E2BIG Too many pages to move. -ENOMEM Not enough memory to allocate control array. -EFAULT Parameters could not be accessed. A test program for move_pages() may be found with the patches on ftp.kernel.org:/pub/linux/kernel/people/christoph/pmig/patches-2.6.17-rc4-mm3 From: Christoph Lameter <clameter@sgi.com> Detailed results for sys_move_pages() Pass a pointer to an integer to get_new_page() that may be used to indicate where the completion status of a migration operation should be placed. This allows sys_move_pags() to report back exactly what happened to each page. Wish there would be a better way to do this. Looks a bit hacky. Signed-off-by: Christoph Lameter <clameter@sgi.com> Cc: Hugh Dickins <hugh@veritas.com> Cc: Jes Sorensen <jes@trained-monkey.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Andi Kleen <ak@muc.de> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation')
-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----------------------------