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Subject: Re: [PATCH] mm/swap: Use page flags to determine LRU list in
 __activate_page()
To:     Anshuman Khandual <khandual@linux.vnet.ibm.com>,
        Michal Hocko <mhocko@kernel.org>
References: <20171019145657.11199-1-khandual@linux.vnet.ibm.com>
 <20171019153322.c4uqalws7l7fdzcx@dhcp22.suse.cz>
 <d01827c0-8858-5688-dc16-1e2f597ec55c@linux.vnet.ibm.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, shli@kernel.org
From:   Anshuman Khandual <khandual@linux.vnet.ibm.com>
Date:   Fri, 27 Oct 2017 09:36:37 +0530
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On 10/23/2017 08:52 AM, Anshuman Khandual wrote:
> On 10/19/2017 09:03 PM, Michal Hocko wrote:
>> On Thu 19-10-17 20:26:57, Anshuman Khandual wrote:
>>> Its already assumed that the PageActive flag is clear on the input
>>> page, hence page_lru(page) will pick the base LRU for the page. In
>>> the same way page_lru(page) will pick active base LRU, once the
>>> flag PageActive is set on the page. This change of LRU list should
>>> happen implicitly through the page flags instead of being hard
>>> coded.
>>
>> The patch description tells what but it doesn't explain _why_? Does the
>> resulting code is better, more optimized or is this a pure readability
>> thing?
> 
> Not really. Not only it removes couple of lines of code but it also
> makes it look more logical from function flow point of view as well.
> 
>>
>> All I can see is that page_lru is more complex and a large part of it
>> can be optimized away which has been done manually here. I suspect the
>> compiler can deduce the same thing.
> 
> Why not ? I mean, that is the essence of the function page_lru() which
> should get us the exact LRU list the page should be on and hence we
> should not hand craft these manually.

Hi Michal,

Did not hear from you on this. So wondering what is the verdict
about this patch ?

- Anshuman


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