linux-kernel - Re: [PATCH] mm: make __paginginit based on CONFIG_MEMORY

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Date:   Tue, 31 Jul 2018 08:49:11 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     osalvador@...hadventures.net
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        kirill.shutemov@...ux.intel.com, iamjoonsoo.kim@....com,
        Mel Gorman <mgorman@...e.de>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, osalvador@...e.de
Subject: Re: [PATCH] mm: make __paginginit based on CONFIG_MEMORY_HOTPLUG

Hi Oscar,

Have you looked into replacing __paginginit via __meminit ? What is
the reason to keep both?

Thank you,
Pavel
On Tue, Jul 31, 2018 at 8:45 AM <osalvador@...hadventures.net> wrote:
>
> From: Oscar Salvador <osalvador@...e.de>
>
> __pagininit macro is being used to mark functions for:
>
> a) Functions that we do not need to keep once the system is fully
>    initialized with regard to memory.
> b) Functions that will be needed for the memory-hotplug code,
>    and because of that we need to keep them after initialization.
>
> Right now, the condition to choose between one or the other is based on
> CONFIG_SPARSEMEM, but I think that this should be changed to be based
> on CONFIG_MEMORY_HOTPLUG.
>
> The reason behind this is that it can very well be that we have CONFIG_SPARSEMEM
> enabled, but not CONFIG_MEMORY_HOTPLUG, and thus, we will not need the
> functions marked as __paginginit to stay around, since no
> memory-hotplug code will call them.
>
> Although the amount of freed bytes is not that big, I think it will
> become more clear what __paginginit is used for.
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>  mm/internal.h | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 33c22754d282..c9170b4f7699 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -392,10 +392,11 @@ static inline struct page *mem_map_next(struct page *iter,
>  /*
>   * FLATMEM and DISCONTIGMEM configurations use alloc_bootmem_node,
>   * so all functions starting at paging_init should be marked __init
> - * in those cases. SPARSEMEM, however, allows for memory hotplug,
> - * and alloc_bootmem_node is not used.
> + * in those cases.
> + * In case that MEMORY_HOTPLUG is enabled, we need to keep those
> + * functions around since they can be called when hot-adding memory.
>   */
> -#ifdef CONFIG_SPARSEMEM
> +#ifdef CONFIG_MEMORY_HOTPLUG
>  #define __paginginit __meminit
>  #else
>  #define __paginginit __init
> --
> 2.13.6
>