From: Dave Hansen <dave.hansen@intel.com>
To: Michal Hocko <mhocko@suse.com>, Wei Yang <richard.weiyang@gmail.com>
Cc: akpm@linux-foundation.org, rientjes@google.com,
linux-mm@kvack.org, kirill.shutemov@linux.intel.com,
bob.picco@hp.com
Subject: Re: [PATCH 2/3] mm/sparse: expand the CONFIG_SPARSEMEM_EXTREME range in __nr_to_section()
Date: Thu, 23 Aug 2018 17:09:12 -0700 [thread overview]
Message-ID: <ebdfe4aa-225c-8239-9f8d-065de8a5ddfc@intel.com> (raw)
In-Reply-To: <20180823132112.GK29735@dhcp22.suse.cz>
On 08/23/2018 06:21 AM, Michal Hocko wrote:
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1155,9 +1155,9 @@ static inline struct mem_section *__nr_to_section(unsigned long nr)
> #ifdef CONFIG_SPARSEMEM_EXTREME
> if (!mem_section)
> return NULL;
> -#endif
> if (!mem_section[SECTION_NR_TO_ROOT(nr)])
> return NULL;
> +#endif
> return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
> }
This patch has no practical effect and only adds unnecessary churn.
#ifdef CONFIG_SPARSEMEM_EXTREME
...
#else
struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
#endif
The compiler knows that NR_SECTION_ROOTS==1 and that
!mem_section[SECTION_NR_TO_ROOT(nr) is always false. It doesn't need
our help.
My goal with the sparsemem code, and code in general is t avoid #ifdefs
whenever possible and limit their scope to the smallest possible area
whenever possible.
next prev parent reply other threads:[~2018-08-24 0:09 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-23 13:07 [PATCH 0/3] trivial code refine for sparsemem Wei Yang
2018-08-23 13:07 ` [PATCH 1/3] mm/sparse: add likely to mem_section[root] check in sparse_index_init() Wei Yang
2018-08-23 13:13 ` Michal Hocko
2018-08-23 22:57 ` Wei Yang
2018-08-24 7:31 ` Michal Hocko
2018-08-24 0:11 ` Dave Hansen
2018-08-24 15:07 ` Wei Yang
2018-09-03 22:27 ` Wei Yang
2018-09-09 1:38 ` Wei Yang
2018-09-10 20:30 ` Dave Hansen
2018-09-11 15:00 ` Wei Yang
2018-08-23 13:07 ` [PATCH 2/3] mm/sparse: expand the CONFIG_SPARSEMEM_EXTREME range in __nr_to_section() Wei Yang
2018-08-23 13:21 ` Michal Hocko
2018-08-23 23:03 ` Wei Yang
2018-08-24 0:09 ` Dave Hansen [this message]
2018-08-24 15:24 ` Wei Yang
2018-08-23 13:07 ` [PATCH 3/3] mm/sparse: use __highest_present_section_nr as the boundary for pfn check Wei Yang
2018-08-23 13:25 ` Michal Hocko
2018-08-23 14:00 ` Oscar Salvador
2018-08-23 19:17 ` Michal Hocko
2018-08-23 20:52 ` Oscar Salvador
2018-08-24 0:15 ` Dave Hansen
2018-08-24 18:11 ` Wei Yang
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