mm/ksm: fix ksm_pages_scanned accounting

Patch series "mm/ksm: fix some accounting problems", v3.

We encountered some abnormal ksm_pages_scanned and ksm_zero_pages during
some random tests.

1. ksm_pages_scanned unchanged even ksmd scanning has progress.
2. ksm_zero_pages maybe -1 in some rare cases.


This patch (of 2):

During testing, I found ksm_pages_scanned is unchanged although the
scan_get_next_rmap_item() did return valid rmap_item that is not NULL.

The reason is the scan_get_next_rmap_item() will return NULL after a full
scan, so ksm_do_scan() just return without accounting of the
ksm_pages_scanned.

Fix it by just putting ksm_pages_scanned accounting in that loop, and it
will be accounted more timely if that loop would last for a long time.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: b348b5f ("mm/ksm: add pages scanned metric")
Signed-off-by: Chengming Zhou <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: xu xin <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ran Xiaokai <[email protected]>
Cc: Stefan Roesch <[email protected]>
Cc: Yang Yang <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: cmzxo

mm/ksm.c

@@ -2754,18 +2754,16 @@ static void ksm_do_scan(unsigned int scan_npages)
 {
 	struct ksm_rmap_item *rmap_item;
 	struct page *page;
-	unsigned int npages = scan_npages;
 
-	while (npages-- && likely(!freezing(current))) {
+	while (scan_npages-- && likely(!freezing(current))) {
 		cond_resched();
 		rmap_item = scan_get_next_rmap_item(&page);
 		if (!rmap_item)
 			return;
 		cmp_and_merge_page(page, rmap_item);
 		put_page(page);
+		ksm_pages_scanned++;
 	}
-
-	ksm_pages_scanned += scan_npages - npages;
 }
 
 static int ksmd_should_run(void)