Messages in this thread Patch in this message | | | Date | Thu, 25 Sep 2008 15:00:04 +0200 | From | Brice Goglin <> | Subject | [RESEND][PATCH] mm: make do_move_pages() complexity linear |
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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 cache the last "pm" pointer to the page array. This way, the next iteration will find the next page in usually 1 while loop (or 0 if called multiple times on the same page, or more if some pages are missing in the list).
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr> Signed-off-by: Nathalie Furmento <Nathalie.Furmento@labri.fr> --- mm/migrate.c | 25 +++++++++++++++++++++---- 1 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c index 2a80136..349b205 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -837,14 +837,29 @@ struct page_to_node { int status; }; +/* + * Allocate a page on the node given as a page_to_node in private. + * + * Cache the _last used_ pm in private so that the next call may find the + * target pm in very few while loops (usually 1) instead of scanning the + * whole pm array. + * We cannot cache the _next_ pm in private (to get 0 while loop in the + * regular case) because it would break the case where new_page_node() + * is called multiple times on the same page (when migrate_pages() tries + * unmap_and_move() multiple times). + */ 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++; + /* save the current pm to reduce the while loop in the next call */ + *pmptr = pm; + if (pm->node == MAX_NUMNODES) return NULL; @@ -926,10 +941,12 @@ 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); -- 1.5.6.5
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