linux-kernel - Re: [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case

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Date:   Tue, 25 Feb 2020 10:10:45 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Baoquan He <bhe@...hat.com>, Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, richardw.yang@...ux.intel.com,
        osalvador@...e.de, dan.j.williams@...el.com, rppt@...ux.ibm.com,
        robin.murphy@....com
Subject: Re: [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP
 case

>>>  include/linux/mmzone.h |   2 +
>>>  mm/sparse.c            | 178 +++++++++++++++++++++++++++++------------
>>>  2 files changed, 127 insertions(+), 53 deletions(-)
>>
>> Why do we need to add so much code to remove a functionality from one
>> memory model?
> 
> Hmm, Dan also asked this before.
> 
> The adding mainly happens in patch 2, 3, 4, including the two newly
> added function defitions, the code comments above them, and those added
> dummy functions for !VMEMMAP.

AFAIKS, it's mostly a bunch of newly added comments on top of functions.
E.g., the comment for fill_subsection_map() alone spans 12 LOC in total.
I do wonder if we have to be that verbose. We are barely that verbose on
MM code (and usually I don't see much benefit unless it's a function
with many users from many different places).

-- 
Thanks,

David / dhildenb