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

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Message-ID: <20171027075727.pc7mj4giv3anewbi@dhcp22.suse.cz>
Date:   Fri, 27 Oct 2017 09:57:27 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
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 Fri 27-10-17 09:36:37, Anshuman Khandual wrote:
> 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 ?

IMHO, there is no reason to change the code as it doesn't solve any real
problem or it doesn't make the code more effective AFAICS.
-- 
Michal Hocko
SUSE Labs