linux-kernel - Re: [PATCH v2] Do not reserve crashkernel high memory if crashkernel low memory reserving failed

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Date:	Tue, 21 Jul 2015 15:31:23 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Baoquan He <bhe@...hat.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, bp@...e.de,
	akpm@...ux-foundation.org, jkosina@...e.cz, vgoyal@...hat.com,
	linux-kernel@...r.kernel.org, yinghai@...nel.org
Subject: Re: [PATCH v2] Do not reserve crashkernel high memory if crashkernel
 low memory reserving failed

Hi, Baoquan

The interface was introduced by Yinghai, ccing him.

On 07/19/15 at 10:53pm, Baoquan He 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 put
> the crashkernel low memory reserving earlier, just between finding
> the crashkernel high memory region and reserving crashkernel high
> memory. Then if crashkernel low memory reserving failed we do not
> reserve crashkernel high memory but return immediately. Users can
> take measures when they found kdump kernel cann't be loaded
> successfully.

So we have 3 sementics now,
crashkernel ,low
crashkernel ,high
crashkernel ,low + crashkernel ,high
For the last case, we need make sure both ,low and ,high reserved,

Can we assume we need both ,low and ,high being ok if one specify
these two types in kernel cmdline?

Also in case one suceed, another fail, should we free the reserved memory?

> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  arch/x86/kernel/setup.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 80f874b..36aeac3 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -513,7 +513,7 @@ 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 */
> @@ -542,7 +542,7 @@ static void __init reserve_crashkernel_low(void)
>  	} else {
>  		/* passed with crashkernel=0,low ? */
>  		if (!low_size)
> -			return;
> +			return 0;
>  	}
>  
>  	low_base = memblock_find_in_range(low_size, (1ULL<<32),
> @@ -552,7 +552,7 @@ static void __init reserve_crashkernel_low(void)
>  		if (!auto_set)
>  			pr_info("crashkernel low reservation failed - No suitable area found.\n");
>  
> -		return;
> +		return -EINVAL;
>  	}
>  
>  	memblock_reserve(low_base, low_size);
> @@ -564,6 +564,7 @@ static void __init reserve_crashkernel_low(void)
>  	crashk_low_res.end   = low_base + low_size - 1;
>  	insert_resource(&iomem_resource, &crashk_low_res);
>  #endif
> +	return 0;
>  }
>  
>  static void __init reserve_crashkernel(void)
> @@ -613,6 +614,10 @@ static void __init reserve_crashkernel(void)
>  			return;
>  		}
>  	}
> +
> +	if (crash_base >= (1ULL<<32) && reserve_crashkernel_low())
> +		return;
> +
>  	memblock_reserve(crash_base, crash_size);
>  
>  	printk(KERN_INFO "Reserving %ldMB of memory at %ldMB "
> @@ -624,9 +629,6 @@ static void __init reserve_crashkernel(void)
>  	crashk_res.start = crash_base;
>  	crashk_res.end   = crash_base + crash_size - 1;
>  	insert_resource(&iomem_resource, &crashk_res);
> -
> -	if (crash_base >= (1ULL<<32))
> -		reserve_crashkernel_low();
>  }
>  #else
>  static void __init reserve_crashkernel(void)
> -- 
> 1.9.3
> 
> 
> --
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