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Date: Sat, 11 Feb 2017 11:24:00 +0900
From: Tejun Heo <tj@kernel.org>
Subject: Re: [RFC PATCH 2/2] mm/sparse: add last_section_nr in sparse_init()
 to reduce some iteration cycle
Message-ID: <20170211022400.GA19050@mtj.duckdns.org>
References: <20170211021829.9646-1-richard.weiyang@gmail.com>
 <20170211021829.9646-2-richard.weiyang@gmail.com>
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In-Reply-To: <20170211021829.9646-2-richard.weiyang@gmail.com>
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To: Wei Yang <richard.weiyang@gmail.com>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org

Hello,

On Sat, Feb 11, 2017 at 10:18:29AM +0800, Wei Yang wrote:
> During the sparse_init(), it iterate on each possible section. On x86_64,
> it would always be (2^19) even there is not much memory. For example, on a
> typical 4G machine, it has only (2^5) to (2^6) present sections. This
> benefits more on a system with smaller memory.
> 
> This patch calculates the last section number from the highest pfn and use
> this as the boundary of iteration.

* How much does this actually matter?  Can you measure the impact?

* Do we really need to add full reverse iterator to just get the
  highest section number?

Thanks.

-- 
tejun

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