linux-kernel - Re: [PATCH] x86/mm: Remove the redundant conditional check

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Message-ID: <20200311011510.GH27711@MiWiFi-R3L-srv>
Date:   Wed, 11 Mar 2020 09:15:10 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, x86@...nel.org
Subject: Re: [PATCH] x86/mm: Remove the redundant conditional check

On 03/10/20 at 03:32pm, Michal Hocko wrote:
> On Tue 10-03-20 22:23:41, Baoquan He wrote:
> > On 03/10/20 at 11:10am, Michal Hocko wrote:
> > > On Sun 08-03-20 09:35:11, Baoquan He wrote:
> > > > In commit f70029bbaacbfa8f0 ("mm, memory_hotplug: drop CONFIG_MOVABLE_NODE"),
> > > > the dependency on CONFIG_MOVABLE_NODE was removed for N_MEMORY, so the
> > > > conditional check in paging_init() doesn't make any sense any more.
> > > > Remove it.
> > > 
> > > Please expand more. I would really have to refresh the intention of the
> > > code but from a quick look at the code CONFIG_HIGHMEM still makes
> > > N_MEMORY != N_NORMAL_MEMORY. So what what does this change mean for that
> > > config?
> > 
> > Thanks for looking into this. I was trying to explain that
> > CONFIG_MOVABLE_NODE made N_MEMORY have chance to take different enum
> > value.
> >  
> > Do you think the below saying is OK to you?
> >  
> > ~~~
> > In commit f70029bbaacb ("mm, memory_hotplug: drop CONFIG_MOVABLE_NODE"),
> > the dependency on CONFIG_MOVABLE_NODE was removed for N_MEMORY.  Before
> > commit f70029bbaacb, CONFIG_HIGHMEM && !CONFIG_MOVABLE_NODE could make
> > (N_MEMORY == N_NORMAL_MEMORY) be true. After commit f70029bbaacb, N_MEMORY
> > doesn't have any chance to be equal to N_NORMAL_MEMORY. So the  conditional
> > check in paging_init() doesn't make any sense any more. Let's remove it.
> 
> Yes this describes the matter much better. I have obviously misread the
> code when looking at it this morning. Being explicit in the changelog
> would have helped at least me. Thanks!

Will update log and repost, thanks.