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

From: Nathan Chancellor <[email-masked]>
Date: Fri, 26 Jul 2019 21:36:31 -0700

On Fri, Jul 26, 2019 at 09:19:52PM -0700, Andrew Morton wrote:
> On Fri, 26 Jul 2019 20:42:05 -0700 Nathan Chancellor <[email-masked]> 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 <[email-masked]>

Thanks for the quick fix!