Messages in this thread Patch in this message | | | Date | Fri, 12 Sep 2008 14:31:22 +0200 | From | Brice Goglin <> | Subject | [PATCH] mm: make do_move_pages() complexity linear |
| |
Page migration is currently very slow because its overhead is quadratic with the number of pages. This is caused by each single page migration doing a linear lookup in the page array in new_page_node().
Since pages are stored in the array order in the pagelist and do_move_pages process this list in order, new_page_node() can increase the "pm" pointer to the page array so that the next iteration will find the next page in 0 or few lookup steps.
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr> Signed-off-by: Nathalie Furmento <Nathalie.Furmento@labri.fr>
--- a/mm/migrate.c +++ b/mm/migrate.c @@ -837,14 +837,23 @@ struct page_to_node { int status; }; +/* + * Allocate a page on the node given as a page_to_node in private. + * Increase private to point to the next page_to_node so that the + * next iteration does not have to traverse the whole pm array. + */ static struct page *new_page_node(struct page *p, unsigned long private, int **result) { - struct page_to_node *pm = (struct page_to_node *)private; + struct page_to_node **pmptr = (struct page_to_node **)private; + struct page_to_node *pm = *pmptr; while (pm->node != MAX_NUMNODES && pm->page != p) pm++; + /* prepare for the next iteration */ + *pmptr = pm + 1; + if (pm->node == MAX_NUMNODES) return NULL; @@ -926,10 +935,12 @@ set_status: pp->status = err; } - if (!list_empty(&pagelist)) + if (!list_empty(&pagelist)) { + /* new_page_node() will modify tmp */ + struct page_to_node *tmp = pm; err = migrate_pages(&pagelist, new_page_node, - (unsigned long)pm); - else + (unsigned long)&tmp); + } else err = -ENOENT; up_read(&mm->mmap_sem);
| |