linux-kernel - Re: [PATCH v1 3/6] mm/memory_hotplug: restrict CONFIG_MEMORY

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Message-ID: <YV63kyvrxt0tx/Ru@localhost.localdomain>
Date:   Thu, 7 Oct 2021 11:02:11 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, Alex Shi <alexs@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Shuah Khan <shuah@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...nel.org>, x86@...nel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v1 3/6] mm/memory_hotplug: restrict CONFIG_MEMORY_HOTPLUG
 to 64 bit

On Wed, Sep 29, 2021 at 04:35:57PM +0200, David Hildenbrand wrote:
> 32 bit support is broken in various ways: for example, we can online
> memory that should actually go to ZONE_HIGHMEM to ZONE_MOVABLE or in
> some cases even to one of the other kernel zones.
> 
> We marked it BROKEN in commit b59d02ed0869 ("mm/memory_hotplug: disable the
> functionality for 32b") almost one year ago. According to that commit
> it might be broken at least since 2017. Further, there is hardly a sane use
> case nowadays.
> 
> Let's just depend completely on 64bit, dropping the "BROKEN" dependency to
> make clear that we are not going to support it again. Next, we'll remove
> some HIGHMEM leftovers from memory hotplug code to clean up.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

> ---
>  mm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ea8762cd8e1e..88273dd5c6d6 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -125,7 +125,7 @@ config MEMORY_HOTPLUG
>  	select MEMORY_ISOLATION
>  	depends on SPARSEMEM
>  	depends on ARCH_ENABLE_MEMORY_HOTPLUG
> -	depends on 64BIT || BROKEN
> +	depends on 64BIT
>  	select NUMA_KEEP_MEMINFO if NUMA
>  
>  config MEMORY_HOTPLUG_DEFAULT_ONLINE
> -- 
> 2.31.1
> 
> 

-- 
Oscar Salvador
SUSE Labs