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

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Date:   Tue, 10 Mar 2020 15:32:40 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
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 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!

-- 
Michal Hocko
SUSE Labs