Re: mmotm 2019-07-24-21-39 uploaded (mm/memcontrol)

Nathan Chancellor
2019-07-27T04:36:39Z

On Fri, Jul 26, 2019 at 09:19:52PM -0700, Andrew Morton wrote:
> On Fri, 26 Jul 2019 20:42:05 -0700 Nathan Chancellor <natechancellor@gmail.com> wrote:
>
> > > @@ -2414,8 +2414,9 @@ void mem_cgroup_handle_over_high(void)
> > > */
> > > clamped_high = max(high, 1UL);
> > >
> > > - overage = ((u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT)
> > > - / clamped_high;
> > > + overage = (u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT;
> > > + do_div(overage, clamped_high);
> > > +
> > > penalty_jiffies = ((u64)overage * overage * HZ)
> > > >> (MEMCG_DELAY_PRECISION_SHIFT + MEMCG_DELAY_SCALING_SHIFT);
> > >
> > > _
> > >
> >
> > This causes a build error on arm:
> >
>
> Ah.
>
> It's rather unclear why that u64 cast is there anyway. We're dealing
> with ulongs all over this code. The below will suffice.

I was thinking the same thing.

> Chris, please take a look?
>
> --- a/mm/memcontrol.c~mm-throttle-allocators-when-failing-reclaim-over-memoryhigh-fix-fix-fix
> +++ a/mm/memcontrol.c
> @@ -2415,7 +2415,7 @@ void mem_cgroup_handle_over_high(void)
> clamped_high = max(high, 1UL);
>
> overage = (u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT;
> - do_div(overage, clamped_high);
> + overage /= clamped_high;
>
> penalty_jiffies = ((u64)overage * overage * HZ)
> >> (MEMCG_DELAY_PRECISION_SHIFT + MEMCG_DELAY_SCALING_SHIFT);
> _
>

I assume this will get folded in with the original patch but for
completeness (multi_v7_defconfig + CONFIG_MEMCG):

Tested-by: Nathan Chancellor <natechancellor@gmail.com>

Thanks for the quick fix!