linux-kernel - Re: [PATCH v2 4/7] mm,memory_hotplug: Enforce struct page size to be multiple of PMD

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Message-ID: <13253f19-d0e9-e27c-046a-c2669c5ee33d@redhat.com>
Date:   Thu, 25 Feb 2021 19:26:50 +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 4/7] mm,memory_hotplug: Enforce struct page size to be
 multiple of PMD

On 09.02.21 14:38, Oscar Salvador wrote:
> When struct page's size is not multiple of PMD, these do not get
> fully populated when adding sections, hence two sections will
> intersect the same the PMD. This goes against the vmemmap-per-device
> premise, so reject it if that is the case.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>   mm/memory_hotplug.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 95695483a622..d3fb036d33fd 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -57,10 +57,11 @@ static __meminit int memmap_on_memory_store(const char *val,
>   					    const struct kernel_param *kp)
>   {
>   	/*
> -	 * Fail silently in case we cannot enable it due to platform constraints.
> +	 * 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))
> +	if (!IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE) ||
> +	    (PMD_SIZE % sizeof(struct page)))
>   		return 0;
>   
>   	return param_set_bool(val, kp);
> 

Squash that into #1 - it's part of basic operation.

-- 
Thanks,

David / dhildenb