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From: Chengming Zhou <chengming.zhou@linux.dev>
Date: Mon, 13 May 2024 10:48:36 +0800
Subject: [PATCH v2 1/2] mm/ksm: fix ksm_pages_scanned accounting
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Message-Id: <20240513-b4-ksm-counters-v2-1-f2520183a8ca@linux.dev>
References: <20240513-b4-ksm-counters-v2-0-f2520183a8ca@linux.dev>
In-Reply-To: <20240513-b4-ksm-counters-v2-0-f2520183a8ca@linux.dev>
To: Andrew Morton <akpm@linux-foundation.org>, 
 David Hildenbrand <david@redhat.com>, Hugh Dickins <hughd@google.com>, 
 Andrea Arcangeli <aarcange@redhat.com>, Stefan Roesch <shr@devkernel.io>, 
 xu xin <xu.xin16@zte.com.cn>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, 
 zhouchengming@bytedance.com, Chengming Zhou <chengming.zhou@linux.dev>

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.

Fixes: b348b5fe2b5f ("mm/ksm: add pages scanned metric")
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
---
 mm/ksm.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index e1034bf1c937..0f9c491552ff 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2753,18 +2753,16 @@ 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)

-- 
2.45.0