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: Hugh 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/ksm.c b/mm/ksm.c
index e10dc24..70daa35 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1830,31 +1830,36 @@
#endif /* CONFIG_MIGRATION */
#ifdef CONFIG_MEMORY_HOTREMOVE
-static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
- unsigned long end_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 @@
/*
* 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: