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
