From: Wei Yang <richard.weiyang@gmail.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Wei Yang <richard.weiyang@gmail.com>,
akpm@linux-foundation.org, mhocko@suse.com, rientjes@google.com,
linux-mm@kvack.org, kirill.shutemov@linux.intel.com,
bob.picco@hp.com
Subject: Re: [PATCH 3/3] mm/sparse: use __highest_present_section_nr as the boundary for pfn check
Date: Sat, 25 Aug 2018 02:11:27 +0800 [thread overview]
Message-ID: <20180824181127.GA11055@WeideMacBook-Pro.local> (raw)
In-Reply-To: <4bb956bd-a061-7122-2c2d-7c910a176681@intel.com>
On Thu, Aug 23, 2018 at 05:15:39PM -0700, Dave Hansen wrote:
>On 08/23/2018 06:07 AM, Wei Yang wrote:
>> And it is known, __highest_present_section_nr is a more strict boundary
>> than NR_MEM_SECTIONS.
>
>What is the benefit of this patch?
>
The original idea is simple: with a more strict boundary, it will has less
computation.
>You're adding a more "strict" boundary, but you're also adding a
>potential cacheline miss and removing optimizations that the compiler
>can make with a constant vs. a variable. Providing absolute bounds
>limits that the compiler knows about can actually be pretty handy for it
>to optimize things
You are right.
I haven't thought about the compiler optimization case.
>
>Do you have *any* analysis to show that this has a benefit? What does
>it do to text size, for instance?
I don't have more analysis about this. Originally, I thought a strict boundary
will have a benefit. But as you mentioned, it loose the compiler optimization.
BTW, I did some tests and found during a normal boot, all the section number
are within NR_MEM_SECTIONS. I am wondering in which case, this check will be
valid and return 0?
--
Wei Yang
Help you, Help me
prev parent reply other threads:[~2018-08-24 18:11 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
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 [this message]
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