mm/ksm: fix ksm_pages_scanned accounting

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From: Chengming Zhou <chengming.zhou@xxxxxxxxx>

commit 730cdc2c72c6905a2eda2fccbbf67dcef1206590 upstream.

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/20240528-b4-ksm-counters-v3-0-34bb358fdc13@xxxxxxxxx
Link: https://lkml.kernel.org/r/20240528-b4-ksm-counters-v3-1-34bb358fdc13@xxxxxxxxx
Fixes: b348b5fe2b5f ("mm/ksm: add pages scanned metric")
Signed-off-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: xu xin <xu.xin16@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
Cc: Stefan Roesch <shr@xxxxxxxxxxxx>
Cc: Yang Yang <yang.yang29@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/ksm.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2486,18 +2486,16 @@ static void ksm_do_scan(unsigned int sca
 {
 	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)


Patches currently in stable-queue which might be from chengming.zhou@xxxxxxxxx are

queue-6.6/mm-ksm-fix-ksm_zero_pages-accounting.patch
queue-6.6/mm-ksm-fix-ksm_pages_scanned-accounting.patch




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