The patch titled
mm: make do_move_pages() complexity linear
has been added to the -mm tree. Its filename is
mm-make-do_move_pages-complexity-linear.patch
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------------------------------------------------------
Subject: mm: make do_move_pages() complexity linear
From: Brice Goglin <Brice.Goglin@xxxxxxxx>
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@xxxxxxxx>
Signed-off-by: Nathalie Furmento <Nathalie.Furmento@xxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff -puN mm/migrate.c~mm-make-do_move_pages-complexity-linear mm/migrate.c
--- a/mm/migrate.c~mm-make-do_move_pages-complexity-linear
+++ a/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);
_
Patches currently in -mm which might be from Brice.Goglin@xxxxxxxx are
mm-make-do_move_pages-complexity-linear.patch
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