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

From: Nathan Chancellor <[email-masked]>
Date: Fri, 26 Jul 2019 20:42:05 -0700

On Thu, Jul 25, 2019 at 04:39:59PM -0700, Andrew Morton wrote:
> On Thu, 25 Jul 2019 15:02:59 -0700 Randy Dunlap <[email-masked]> wrote:
> 
> > On 7/24/19 9:40 PM, [email-masked] wrote:
> > > The mm-of-the-moment snapshot 2019-07-24-21-39 has been uploaded to
> > > 
> > >    http://www.ozlabs.org/~akpm/mmotm/
> > > 
> > > mmotm-readme.txt says
> > > 
> > > README for mm-of-the-moment:
> > > 
> > > http://www.ozlabs.org/~akpm/mmotm/
> > > 
> > > This is a snapshot of my -mm patch queue.  Uploaded at random hopefully
> > > more than once a week.
> > > 
> > > You will need quilt to apply these patches to the latest Linus release (5.x
> > > or 5.x-rcY).  The series file is in broken-out.tar.gz and is duplicated in
> > > http://ozlabs.org/~akpm/mmotm/series
> > > 
> > 
> > on i386:
> > 
> > ld: mm/memcontrol.o: in function `mem_cgroup_handle_over_high':
> > memcontrol.c:(.text+0x6235): undefined reference to `__udivdi3'
> 
> Thanks.  This?
> 
> --- a/mm/memcontrol.c~mm-throttle-allocators-when-failing-reclaim-over-memoryhigh-fix-fix
> +++ a/mm/memcontrol.c
> @@ -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:

In file included from ../arch/arm/include/asm/div64.h:127,
                 from ../include/linux/kernel.h:18,
                 from ../include/linux/page_counter.h:6,
                 from ../mm/memcontrol.c:25:
../mm/memcontrol.c: In function 'mem_cgroup_handle_over_high':
../include/asm-generic/div64.h:222:28: warning: comparison of distinct pointer types lacks a cast
  222 |  (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
      |                            ^~
../mm/memcontrol.c:2423:2: note: in expansion of macro 'do_div'
 2423 |  do_div(overage, clamped_high);
      |  ^~~~~~
In file included from ../arch/arm/include/asm/atomic.h:11,
                 from ../include/linux/atomic.h:7,
                 from ../include/linux/page_counter.h:5,
                 from ../mm/memcontrol.c:25:
../include/asm-generic/div64.h:235:25: warning: right shift count >= width of type [-Wshift-count-overflow]
  235 |  } else if (likely(((n) >> 32) == 0)) {  \
      |                         ^~
../include/linux/compiler.h:77:40: note: in definition of macro 'likely'
   77 | # define likely(x) __builtin_expect(!!(x), 1)
      |                                        ^
../mm/memcontrol.c:2423:2: note: in expansion of macro 'do_div'
 2423 |  do_div(overage, clamped_high);
      |  ^~~~~~
In file included from ../arch/arm/include/asm/div64.h:127,
                 from ../include/linux/kernel.h:18,
                 from ../include/linux/page_counter.h:6,
                 from ../mm/memcontrol.c:25:
../include/asm-generic/div64.h:239:22: error: passing argument 1 of '__div64_32' from incompatible pointer type [-Werror=incompatible-pointer-types]
  239 |   __rem = __div64_32(&(n), __base); \
      |                      ^~~~
      |                      |
      |                      long unsigned int *
../mm/memcontrol.c:2423:2: note: in expansion of macro 'do_div'
 2423 |  do_div(overage, clamped_high);
      |  ^~~~~~
In file included from ../include/linux/kernel.h:18,
                 from ../include/linux/page_counter.h:6,
                 from ../mm/memcontrol.c:25:
../arch/arm/include/asm/div64.h:33:45: note: expected 'uint64_t *' {aka 'long long unsigned int *'} but argument is of type 'long unsigned int *'
   33 | static inline uint32_t __div64_32(uint64_t *n, uint32_t base)
      |                                   ~~~~~~~~~~^
cc1: some warnings being treated as errors
make[3]: *** [../scripts/Makefile.build:274: mm/memcontrol.o] Error 1
make[2]: *** [../Makefile:1768: mm/memcontrol.o] Error 2
make[1]: *** [/home/nathan/cbl/linux-next/Makefile:330: __build_one_by_one] Error 2
make: *** [Makefile:179: sub-make] Error 2

I fixed it up like so but no idea if that is the ideal function to use.

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5c7b9facb0eb..04b621f1cb6b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2419,8 +2419,8 @@ 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 = div64_u64((u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT,
+			    clamped_high);
 
 	penalty_jiffies = ((u64)overage * overage * HZ)
 		>> (MEMCG_DELAY_PRECISION_SHIFT + MEMCG_DELAY_SCALING_SHIFT);