* [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio
@ 2023-12-18 3:16 Jingbo Xu
2023-12-18 3:29 ` Jingbo Xu
2023-12-18 18:21 ` Andrew Morton
0 siblings, 2 replies; 4+ messages in thread
From: Jingbo Xu @ 2023-12-18 3:16 UTC (permalink / raw)
To: shr, akpm; +Cc: linux-mm, linux-kernel, joseph.qi
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);
--
2.19.1.6.gb485710b
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio
2023-12-18 3:16 [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio Jingbo Xu
@ 2023-12-18 3:29 ` Jingbo Xu
2023-12-18 18:21 ` Andrew Morton
1 sibling, 0 replies; 4+ messages in thread
From: Jingbo Xu @ 2023-12-18 3:29 UTC (permalink / raw)
To: shr, akpm; +Cc: linux-mm, linux-kernel, joseph.qi, linux-fsdevel
+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);
>
--
Thanks,
Jingbo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio
2023-12-18 3:16 [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio Jingbo Xu
2023-12-18 3:29 ` Jingbo Xu
@ 2023-12-18 18:21 ` Andrew Morton
2023-12-19 2:03 ` Jingbo Xu
1 sibling, 1 reply; 4+ messages in thread
From: Andrew Morton @ 2023-12-18 18:21 UTC (permalink / raw)
To: Jingbo Xu; +Cc: shr, linux-mm, linux-kernel, joseph.qi
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?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio
2023-12-18 18:21 ` Andrew Morton
@ 2023-12-19 2:03 ` Jingbo Xu
0 siblings, 0 replies; 4+ messages in thread
From: Jingbo Xu @ 2023-12-19 2:03 UTC (permalink / raw)
To: Andrew Morton; +Cc: shr, linux-mm, linux-kernel, joseph.qi
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%.
--
Thanks,
Jingbo
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-12-19 2:03 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-12-18 3:16 [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio Jingbo Xu
2023-12-18 3:29 ` Jingbo Xu
2023-12-18 18:21 ` Andrew Morton
2023-12-19 2:03 ` Jingbo Xu
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).