linux-kernel - Re: [PATCH] mm/memblock.c: make the index explicit argument of for_each_memblock

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Message-ID: <20170913105539.ijfwfrfbn3bici6g@dhcp22.suse.cz>
Date:   Wed, 13 Sep 2017 12:55:39 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Gioh Kim <gi-oh.kim@...fitbricks.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/memblock.c: make the index explicit argument of
 for_each_memblock_type

On Wed 13-09-17 11:06:06, Gioh Kim wrote:
> for_each_memblock_type macro function uses idx variable that is
> the local variable of caller. This patch makes for_each_memblock_type
> use only its own arguments.

strictly speaking this changelog doesn't explain _why_ the original code
is wrong/suboptimal and why you are changing that. I would use the
folloging

"
for_each_memblock_type macro function relies on idx variable defined in
the caller context. Silent macro arguments are almost always wrong thing
to do. They make code harder to read and easier to get wrong. Let's
use an explicit iterator parameter for for_each_memblock_type and make
the code more obious. This patch is a mere cleanup and it shouldn't
introduce any functional change.
"

> Signed-off-by: Gioh Kim <gi-oh.kim@...fitbricks.com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  include/linux/memblock.h | 8 ++++----
>  mm/memblock.c            | 8 ++++----
>  2 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index bae11c7e7bf3..ce0e5634c2f9 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -389,10 +389,10 @@ static inline unsigned long memblock_region_reserved_end_pfn(const struct memblo
>  	     region < (memblock.memblock_type.regions + memblock.memblock_type.cnt);	\
>  	     region++)
>  
> -#define for_each_memblock_type(memblock_type, rgn)			\
> -	for (idx = 0, rgn = &memblock_type->regions[0];			\
> -	     idx < memblock_type->cnt;					\
> -	     idx++, rgn = &memblock_type->regions[idx])
> +#define for_each_memblock_type(i, memblock_type, rgn)			\
> +	for (i = 0, rgn = &memblock_type->regions[0];			\
> +	     i < memblock_type->cnt;					\
> +	     i++, rgn = &memblock_type->regions[i])
>  
>  #ifdef CONFIG_MEMTEST
>  extern void early_memtest(phys_addr_t start, phys_addr_t end);
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 91205780e6b1..18dbb69086bc 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -533,7 +533,7 @@ int __init_memblock memblock_add_range(struct memblock_type *type,
>  	base = obase;
>  	nr_new = 0;
>  
> -	for_each_memblock_type(type, rgn) {
> +	for_each_memblock_type(idx, type, rgn) {
>  		phys_addr_t rbase = rgn->base;
>  		phys_addr_t rend = rbase + rgn->size;
>  
> @@ -637,7 +637,7 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>  		if (memblock_double_array(type, base, size) < 0)
>  			return -ENOMEM;
>  
> -	for_each_memblock_type(type, rgn) {
> +	for_each_memblock_type(idx, type, rgn) {
>  		phys_addr_t rbase = rgn->base;
>  		phys_addr_t rend = rbase + rgn->size;
>  
> @@ -1715,7 +1715,7 @@ static void __init_memblock memblock_dump(struct memblock_type *type)
>  
>  	pr_info(" %s.cnt  = 0x%lx\n", type->name, type->cnt);
>  
> -	for_each_memblock_type(type, rgn) {
> +	for_each_memblock_type(idx, type, rgn) {
>  		char nid_buf[32] = "";
>  
>  		base = rgn->base;
> @@ -1739,7 +1739,7 @@ memblock_reserved_memory_within(phys_addr_t start_addr, phys_addr_t end_addr)
>  	unsigned long size = 0;
>  	int idx;
>  
> -	for_each_memblock_type((&memblock.reserved), rgn) {
> +	for_each_memblock_type(idx, (&memblock.reserved), rgn) {
>  		phys_addr_t start, end;
>  
>  		if (rgn->base + rgn->size < start_addr)
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs