linux-kernel - Re: [PATCH v2 5/7] mm,memory_hotplug: Enforce pageblock alignment when memmap_on

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Message-ID: <9fcd9246-8e27-2991-a32f-539d9a430514@redhat.com>
Date:   Thu, 25 Feb 2021 19:27:33 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>, VlastimilBabkavbabka@...e.cz,
        pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v2 5/7] mm,memory_hotplug: Enforce pageblock alignment
 when memmap_on_memory

On 09.02.21 14:38, Oscar Salvador wrote:
> Many places expects us to pass a pageblock aligned range.
> E.g: memmap_init_zone() needs a pageblock aligned range in order
> to set the proper migrate type for it.
> online_pages() needs to operate on a pageblock aligned range for
> isolation purposes.
> 
> Make sure we disable the feature in case we cannot guarantee the
> right alignment.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>   mm/memory_hotplug.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index d3fb036d33fd..1a4d5dd1a2c8 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -56,12 +56,16 @@ static int memmap_on_memory_show(char *buffer, const struct kernel_param *kp)
>   static __meminit int memmap_on_memory_store(const char *val,
>   					    const struct kernel_param *kp)
>   {
> +	unsigned long pageblock_size = PFN_PHYS(pageblock_nr_pages);
> +
>   	/*
>   	 * Fail silently in case we cannot enable it due to system constraints.
>   	 * User can always check whether it is enabled or not via /sys/module.
>   	 */
>   	if (!IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE) ||
> -	    (PMD_SIZE % sizeof(struct page)))
> +	    (PMD_SIZE % sizeof(struct page)) ||
> +	    !(MIN_MEMORY_BLOCK_SIZE - PMD_SIZE) ||
> +	    !(MIN_MEMORY_BLOCK_SIZE - PMD_SIZE) % pageblock_size)
>   		return 0;
>   
>   	return param_set_bool(val, kp);
> 

Dito, rather squash in #1 and add a comment explaining what's happening 
there.

-- 
Thanks,

David / dhildenb