+ mm-rework-calculation-of-bdi_min_ratio-in-bdi_set_min_ratio.patch added to -mm tree

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The patch titled
     Subject: mm: rework calculation of bdi_min_ratio in bdi_set_min_ratio
has been added to the -mm tree.  Its filename is
     mm-rework-calculation-of-bdi_min_ratio-in-bdi_set_min_ratio.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-rework-calculation-of-bdi_min_ratio-in-bdi_set_min_ratio.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-rework-calculation-of-bdi_min_ratio-in-bdi_set_min_ratio.patch

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------------------------------------------------------
From: Chen Wandun <chenwandun@xxxxxxxxxx>
Subject: mm: rework calculation of bdi_min_ratio in bdi_set_min_ratio

In function bdi_set_min_ratio, min_ratio is unsigned int, it will
result underflow when setting min_ratio below bdi->min_ratio, it
is confusing. Rework it, no functional change.

Link: https://lkml.kernel.org/r/20220422095159.2858305-1-chenwandun@xxxxxxxxxx
Signed-off-by: Chen Wandun <chenwandun@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page-writeback.c |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

--- a/mm/page-writeback.c~mm-rework-calculation-of-bdi_min_ratio-in-bdi_set_min_ratio
+++ a/mm/page-writeback.c
@@ -650,18 +650,25 @@ static unsigned int bdi_min_ratio;
 
 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 {
+	unsigned int delta;
 	int ret = 0;
 
 	spin_lock_bh(&bdi_lock);
 	if (min_ratio > bdi->max_ratio) {
 		ret = -EINVAL;
 	} else {
-		min_ratio -= bdi->min_ratio;
-		if (bdi_min_ratio + min_ratio < 100) {
-			bdi_min_ratio += min_ratio;
-			bdi->min_ratio += min_ratio;
+		if (min_ratio < bdi->min_ratio) {
+			delta = bdi->min_ratio - min_ratio;
+			bdi_min_ratio -= delta;
+			bdi->min_ratio = min_ratio;
 		} else {
-			ret = -EINVAL;
+			delta = min_ratio - bdi->min_ratio;
+			if (bdi_min_ratio + delta < 100) {
+				bdi_min_ratio += delta;
+				bdi->min_ratio = min_ratio;
+			} else {
+				ret = -EINVAL;
+			}
 		}
 	}
 	spin_unlock_bh(&bdi_lock);
_

Patches currently in -mm which might be from chenwandun@xxxxxxxxxx are

mm-rework-calculation-of-bdi_min_ratio-in-bdi_set_min_ratio.patch
mm-page_alloc-simplify-update-of-pgdat-in-wake_all_kswapds.patch




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