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

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Date:   Fri, 26 Jul 2019 21:36:31 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Randy Dunlap <rdunlap@...radead.org>, broonie@...nel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-next@...r.kernel.org, mhocko@...e.cz,
        mm-commits@...r.kernel.org, sfr@...b.auug.org.au,
        Chris Down <chris@...isdown.name>
Subject: Re: mmotm 2019-07-24-21-39 uploaded (mm/memcontrol)

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@...il.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@...il.com>

Thanks for the quick fix!