linux-kernel - Re: [PATCH] [v2] mm: make arch_has_descending_max_zone

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Message-ID: <5a5e21d1-b346-2943-3ec0-e84f03551998@suse.cz>
Date:   Mon, 17 Apr 2023 12:05:34 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Arnd Bergmann <arnd@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, llvm@...ts.linux.dev,
        Vineet Gupta <vgupta@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] [v2] mm: make arch_has_descending_max_zone_pfns() static

On 4/15/23 10:18, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> clang produces a build failure on x86 for some randconfig builds
> after a change that moves around code to mm/mm_init.c:
> 
> Cannot find symbol for section 2: .text.
> mm/mm_init.o: failed
> 
> I have not been able to figure out why this happens, but the __weak
> annotation on arch_has_descending_max_zone_pfns() is the trigger here.
> 
> Removing the weak function in favor of an open-coded Kconfig option
> check avoids the problem and becomes clearer as well as better to
> optimize by the compiler.
> 
> Fixes: 9420f89db2dd ("mm: move most of core MM initialization to mm/mm_init.c")
> Cc: llvm@...ts.linux.dev
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Makes sense if there's only a single arch that has the special case.

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
> v2: fix logic bug reported-by: kernel test robot <oliver.sang@...el.com>,
> see https://lore.kernel.org/oe-lkp/202304151422.5e4d380b-oliver.sang@intel.com
> ---
>  arch/arc/mm/init.c | 5 -----
>  include/linux/mm.h | 1 -
>  mm/mm_init.c       | 4 ++--
>  3 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
> index ce4e939a7f07..2b89b6c53801 100644
> --- a/arch/arc/mm/init.c
> +++ b/arch/arc/mm/init.c
> @@ -74,11 +74,6 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
>  		base, TO_MB(size), !in_use ? "Not used":"");
>  }
>  
> -bool arch_has_descending_max_zone_pfns(void)
> -{
> -	return !IS_ENABLED(CONFIG_ARC_HAS_PAE40);
> -}
> -
>  /*
>   * First memory setup routine called from setup_arch()
>   * 1. setup swapper's mm @init_mm
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 63acf4a598fe..75d8adce0aee 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3061,7 +3061,6 @@ extern void setup_per_cpu_pageset(void);
>  extern int min_free_kbytes;
>  extern int watermark_boost_factor;
>  extern int watermark_scale_factor;
> -extern bool arch_has_descending_max_zone_pfns(void);
>  
>  /* nommu.c */
>  extern atomic_long_t mmap_pages_allocated;
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 35302b7bca83..7f7f9c677854 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1754,9 +1754,9 @@ static void __init free_area_init_memoryless_node(int nid)
>   * Some architectures, e.g. ARC may have ZONE_HIGHMEM below ZONE_NORMAL. For
>   * such cases we allow max_zone_pfn sorted in the descending order
>   */
> -bool __weak arch_has_descending_max_zone_pfns(void)
> +static bool arch_has_descending_max_zone_pfns(void)
>  {
> -	return false;
> +	return IS_ENABLED(CONFIG_ARC) && !IS_ENABLED(CONFIG_ARC_HAS_PAE40);
>  }
>  
>  /**