linux-kernel - Re: [PATCH] mm/swap: Use page flags to determine LRU list in __activate

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Message-Id: <2fc28494-d0d2-9b65-aeb7-1ccabf210917@linux.vnet.ibm.com>
Date:   Fri, 27 Oct 2017 09:36:37 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, shli@...nel.org
Subject: Re: [PATCH] mm/swap: Use page flags to determine LRU list in
 __activate_page()

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