| Message ID | 20231218031640.77983-1-jefflexu@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: fix arithmetic for bdi min_ratio and max_ratio | expand |
+cc fsdevel On 12/18/23 11:16 AM, Jingbo Xu wrote: > bdi->[min|max]_ratio are both part per million. Fix the wrong > arithmetic when setting bdi's min_ratio and max_ratio. > > Fixes: efc3e6ad53ea ("mm: split off __bdi_set_max_ratio() function") > Fixes: 8021fb3232f2 ("mm: split off __bdi_set_min_ratio() function") > Reported-by: Joseph Qi <joseph.qi@linux.alibaba.com> > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com> > --- > mm/page-writeback.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index ee2fd6a6af40..b393b3281ce9 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -692,7 +692,6 @@ static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ra > > if (min_ratio > 100 * BDI_RATIO_SCALE) > return -EINVAL; > - min_ratio *= BDI_RATIO_SCALE; > > spin_lock_bh(&bdi_lock); > if (min_ratio > bdi->max_ratio) { > @@ -729,7 +728,8 @@ static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ra > ret = -EINVAL; > } else { > bdi->max_ratio = max_ratio; > - bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; > + bdi->max_prop_frac = div64_u64(FPROP_FRAC_BASE * max_ratio, > + 100UL * BDI_RATIO_SCALE); > } > spin_unlock_bh(&bdi_lock); >
On Mon, 18 Dec 2023 11:16:40 +0800 Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > bdi->[min|max]_ratio are both part per million. Fix the wrong > arithmetic when setting bdi's min_ratio and max_ratio. > > Fixes: efc3e6ad53ea ("mm: split off __bdi_set_max_ratio() function") > Fixes: 8021fb3232f2 ("mm: split off __bdi_set_min_ratio() function") As we have two Fixes:, it would be better to have two patches please. > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -692,7 +692,6 @@ static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ra > > if (min_ratio > 100 * BDI_RATIO_SCALE) > return -EINVAL; > - min_ratio *= BDI_RATIO_SCALE; > > spin_lock_bh(&bdi_lock); > if (min_ratio > bdi->max_ratio) { > @@ -729,7 +728,8 @@ static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ra > ret = -EINVAL; > } else { > bdi->max_ratio = max_ratio; > - bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; > + bdi->max_prop_frac = div64_u64(FPROP_FRAC_BASE * max_ratio, > + 100UL * BDI_RATIO_SCALE); > } > spin_unlock_bh(&bdi_lock); Does this change have any observable runtime effects? If so, what are they?
On 12/19/23 2:21 AM, Andrew Morton wrote: > On Mon, 18 Dec 2023 11:16:40 +0800 Jingbo Xu <jefflexu@linux.alibaba.com> wrote: > >> bdi->[min|max]_ratio are both part per million. Fix the wrong >> arithmetic when setting bdi's min_ratio and max_ratio. >> >> Fixes: efc3e6ad53ea ("mm: split off __bdi_set_max_ratio() function") >> Fixes: 8021fb3232f2 ("mm: split off __bdi_set_min_ratio() function") > > As we have two Fixes:, it would be better to have two patches please. Sounds reasonable. Thanks. > >> --- a/mm/page-writeback.c >> +++ b/mm/page-writeback.c >> @@ -692,7 +692,6 @@ static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ra >> >> if (min_ratio > 100 * BDI_RATIO_SCALE) >> return -EINVAL; >> - min_ratio *= BDI_RATIO_SCALE; This indeed has visible runtime effect as follows: # cat /sys/class/bdi/253\:0/min_ratio 0 # cat /sys/class/bdi/253\:0/max_ratio 100 # echo 1 > /sys/class/bdi/253\:0/min_ratio -bash: echo: write error: Invalid argument Setting min_ratio will fail with -EINVAL, as the above code tries to set min_ratio with (min_ratio * BDI_RATIO_SCALE)%, i.e. 10000% in the above example. >> >> spin_lock_bh(&bdi_lock); >> if (min_ratio > bdi->max_ratio) { >> @@ -729,7 +728,8 @@ static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ra >> ret = -EINVAL; >> } else { >> bdi->max_ratio = max_ratio; >> - bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; >> + bdi->max_prop_frac = div64_u64(FPROP_FRAC_BASE * max_ratio, >> + 100UL * BDI_RATIO_SCALE); >> } >> spin_unlock_bh(&bdi_lock); This one has no visible runtime effect, but I believe this would affect the incrementing of writeout completion count when max_ratio is not 100%.
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index ee2fd6a6af40..b393b3281ce9 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -692,7 +692,6 @@ static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ra if (min_ratio > 100 * BDI_RATIO_SCALE) return -EINVAL; - min_ratio *= BDI_RATIO_SCALE; spin_lock_bh(&bdi_lock); if (min_ratio > bdi->max_ratio) { @@ -729,7 +728,8 @@ static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ra ret = -EINVAL; } else { bdi->max_ratio = max_ratio; - bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; + bdi->max_prop_frac = div64_u64(FPROP_FRAC_BASE * max_ratio, + 100UL * BDI_RATIO_SCALE); } spin_unlock_bh(&bdi_lock);
bdi->[min|max]_ratio are both part per million. Fix the wrong arithmetic when setting bdi's min_ratio and max_ratio. Fixes: efc3e6ad53ea ("mm: split off __bdi_set_max_ratio() function") Fixes: 8021fb3232f2 ("mm: split off __bdi_set_min_ratio() function") Reported-by: Joseph Qi <joseph.qi@linux.alibaba.com> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com> --- mm/page-writeback.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)