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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/20240528-b4-ksm-counters-v3-0-34bb358fdc13@linux.dev
Link: https://lkml.kernel.org/r/20240528-b4-ksm-counters-v3-1-34bb358fdc13@linux.dev
Fixes: b348b5fe2b ("mm/ksm: add pages scanned metric")
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: xu xin <xu.xin16@zte.com.cn>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Stefan Roesch <shr@devkernel.io>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Chengming Zhou 2024-05-28 13:15:21 +08:00 committed by Andrew Morton
parent 2ef3cec44c
commit 730cdc2c72
1 changed files with 2 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
mm/ksm.c
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@ -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)