linux-kernel - Re: [PATCH] mm/hotplug: Only respect mem= parameter during boot stage

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Date:   Mon, 9 Dec 2019 10:43:14 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, jgross@...e.com, william.kucharski@...cle.com,
        mingo@...nel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] mm/hotplug: Only respect mem= parameter during boot stage

On 06.12.19 16:05, Baoquan He wrote:
> In commit 357b4da50a62 ("x86: respect memory size limiting via mem=
> parameter") a global varialbe global max_mem_size is added to store
> the value which is parsed from 'mem= '. This truly stops those
> DIMM from being added into system memory during boot.
> 
> However, it also limits the later memory hotplug functionality. Any
> memory board can't be hot added any more if its region is beyond the
> max_mem_size. System will print error like below:
> 
> [  216.387164] acpi PNP0C80:02: add_memory failed
> [  216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error
> [  216.392187] acpi PNP0C80:02: Enumeration failure
> 
> From document of 'mem =' parameter, it should be a restriction during
> boot, but not impact the system memory adding/removing after booting.
> 
>   mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
> 
> So fix it by also checking if it's during SYSTEM_BOOTING stage when
> restrict memory adding. Otherwise, skip the restriction.
> 
> Fixes: 357b4da50a62 ("x86: respect memory size limiting via mem= parameter")
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  mm/memory_hotplug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 55ac23ef11c1..5466a0a00901 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -105,7 +105,7 @@ static struct resource *register_memory_resource(u64 start, u64 size)
>  	unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>  	char *resource_name = "System RAM";
>  
> -	if (start + size > max_mem_size)
> +	if (start + size > max_mem_size && system_state == SYSTEM_BOOTING)
>  		return ERR_PTR(-E2BIG);
>  
>  	/*
> 

Sounds sane to me.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb