Merge branch 'for-linus' of git://git390.marist.edu/pub/scm/linux-2.6

[pandora-kernel.git] / Documentation / vm / page_migration

diff --git a/Documentation/vm/page_migration b/Documentation/vm/page_migration
index 0a5d5fb..6513fe2 100644 (file)
--- a/Documentation/vm/page_migration
+++ b/Documentation/vm/page_migration
@@ -18,20 +18,27 @@ migrate_pages function call takes two sets of nodes and moves pages of a
 process that are located on the from nodes to the destination nodes.
 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://ftp.suse.com/pub/people/ak). numactl provided 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 pages of
-a process are located. See also the numa_maps manpage in the numactl package.
+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
+pages of a process are located. See also the numa_maps documentation in the
+proc(5) man page.
 
 Manual migration is useful if for example the scheduler has relocated
 a process to a processor on a distant node. A batch scheduler or an
 administrator may detect the situation and move the pages of the process
-nearer to the new processor. At some point in the future we may have
-some mechanism in the scheduler that will automatically move the pages.
+nearer to the new processor. The kernel itself does only provide
+manual page migration support. Automatic page migration may be implemented
+through user space processes that move pages. A special function call
+"move_pages" allows the moving of individual pages within a process.
+A NUMA profiler may f.e. obtain a log showing frequent off node
+accesses and may use the result to move pages to more advantageous
+locations.
 
 Larger installations usually partition the system using cpusets into
 sections of nodes. Paul Jackson has equipped cpusets with the ability to
-move pages when a task is moved to another cpuset (See ../cpusets.txt).
+move pages when a task is moved to another cpuset (See
+Documentation/cgroups/cpusets.txt).
 Cpusets allows the automation of process locality. If a task is moved to
 a new cpuset then also all its pages are moved with it so that the
 performance of the process does not sink dramatically. Also the pages
@@ -62,22 +69,14 @@ A. In kernel use of migrate_pages()
    It also prevents the swapper or other scans to encounter
    the page.
 
-2. Generate a list of newly allocates pages. These pages will contain the
-   contents of the pages from the first list after page migration is
-   complete.
+2. We need to have a function of type new_page_t that can be
+   passed to migrate_pages(). This function should figure out
+   how to allocate the correct new page given the old page.
 
 3. The migrate_pages() function is called which attempts
-   to do the migration. It returns the moved pages in the
-   list specified as the third parameter and the failed
-   migrations in the fourth parameter. When the function
-   returns the first list will contain the pages that could still be retried.
-
-4. The leftover pages of various types are returned
-   to the LRU using putback_to_lru_pages() or otherwise
-   disposed of. The pages will still have the refcount as
-   increased by isolate_lru_pages() if putback_to_lru_pages() is not
-   used! The kernel may want to handle the various cases of failures in
-   different ways.
+   to do the migration. It will call the function to allocate
+   the new page for each page that is considered for
+   moving.
 
 B. How migrate_pages() works
 ----------------------------