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Commit ee0ea59c authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

ksm: reorganize ksm_check_stable_tree 



Memory hotremove's ksm_check_stable_tree() is pitifully inefficient
(restarting whenever it finds a stale node to remove), but rearrange so
that at least it does not needlessly restart from nid 0 each time.  And
add a couple of comments: here is why we keep pfn instead of page.

Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e850dcf5

mm/ksm.c

+22 −16
Original line number Diff line number Diff line
@@ -1830,31 +1830,36 @@ void ksm_migrate_page(struct page *newpage, struct page *oldpage) 
#endif /* CONFIG_MIGRATION */



#ifdef CONFIG_MEMORY_HOTREMOVE

static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,

static void ksm_check_stable_tree(unsigned long start_pfn,

				  unsigned long end_pfn)

{

	struct stable_node *stable_node;

	struct rb_node *node;

	int nid;



	for (nid = 0; nid < nr_node_ids; nid++)

		for (node = rb_first(&root_stable_tree[nid]); node;

				node = rb_next(node)) {

			struct stable_node *stable_node;



	for (nid = 0; nid < nr_node_ids; nid++) {

		node = rb_first(&root_stable_tree[nid]);

		while (node) {

			stable_node = rb_entry(node, struct stable_node, node);

			if (stable_node->kpfn >= start_pfn &&

			    stable_node->kpfn < end_pfn)

				return stable_node;

			    stable_node->kpfn < end_pfn) {

				/*

				 * Don't get_ksm_page, page has already gone:

				 * which is why we keep kpfn instead of page*

				 */

				remove_node_from_stable_tree(stable_node);

				node = rb_first(&root_stable_tree[nid]);

			} else

				node = rb_next(node);

			cond_resched();

		}

	}



	return NULL;

}



static int ksm_memory_callback(struct notifier_block *self,

			       unsigned long action, void *arg)

{

	struct memory_notify *mn = arg;

	struct stable_node *stable_node;



	switch (action) {

	case MEM_GOING_OFFLINE:
@@ -1874,11 +1879,12 @@ static int ksm_memory_callback(struct notifier_block *self, 
		/*

		 * Most of the work is done by page migration; but there might

		 * be a few stable_nodes left over, still pointing to struct

		 * pages which have been offlined: prune those from the tree.

		 * pages which have been offlined: prune those from the tree,

		 * otherwise get_ksm_page() might later try to access a

		 * non-existent struct page.

		 */

		while ((stable_node = ksm_check_stable_tree(mn->start_pfn,

					mn->start_pfn + mn->nr_pages)) != NULL)

			remove_node_from_stable_tree(stable_node);

		ksm_check_stable_tree(mn->start_pfn,

				      mn->start_pfn + mn->nr_pages);

		/* fallthrough */



	case MEM_CANCEL_OFFLINE: