linux-kernel - Re: [Patch v4] Do not reserve crashkernel high memory if crashkernel low memory reserving failed

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Date:	Tue, 22 Sep 2015 12:54:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Baoquan He <bhe@...hat.com>
Cc:	yinghai@...nel.org, dyoung@...hat.com, jroedel@...e.de,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, bp@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [Patch v4] Do not reserve crashkernel high memory if
 crashkernel low memory reserving failed

On Tue, 22 Sep 2015 19:48:14 +0800 Baoquan He <bhe@...hat.com> wrote:

> People reported that when allocating crashkernel memory using
> ",high" and ",low" syntax, there were cases where the reservation
> of the "high" portion succeeds, but the reservation of the "low"
> portion fails. Then kexec can load kdump kernel successfully, but
> the boot of kdump kernel fails as there's no low memory. This is
> because allocation of low memory for kdump kernel can fail on large
> systems for reasons. E.g it could be manually specified crashkernel
> low memory is too large to find in memblock region.
> 
> In this patch add return value for reserve_crashkernel_low. Then
> try to reserve crashkernel low memory after crashkernel high memory
> has been allocated. If crashkernel low memory reservation failed
> free crashkernel high memory and return. User can take measures
> when they found kdump kernel cann't be loaded successfully.
>
> ...
>
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -493,7 +493,7 @@ static void __init memblock_x86_reserve_range_setup_data(void)
>  # define CRASH_KERNEL_ADDR_HIGH_MAX	MAXMEM
>  #endif
>  
> -static void __init reserve_crashkernel_low(void)
> +static int __init reserve_crashkernel_low(void)
>  {
>  #ifdef CONFIG_X86_64
>  	const unsigned long long alignment = 16<<20;	/* 16M */
> @@ -522,17 +522,15 @@ static void __init reserve_crashkernel_low(void)
>  	} else {
>  		/* passed with crashkernel=0,low ? */
>  		if (!low_size)
> -			return;
> +			return 0;

What's happening here?  It's returning "success" when
parse_crashkernel_low() fails?

>  	}
>  
>  	low_base = memblock_find_in_range(low_size, (1ULL<<32),
>  					low_size, alignment);
>  
>  	if (!low_base) {
> -		if (!auto_set)
> -			pr_info("crashkernel low reservation failed - No suitable area found.\n");
> -
> -		return;
> +		pr_info("crashkernel low reservation failed - No suitable area found.\n");

That's not a terribly useful message.  If kdump is now unavailable and
the operator needs to take some remedial action then we should inform
them of this.

Also, such a message should have higher severity than KERN_INFO?

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