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

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Message-ID: <20151014084328.GU10641@suse.de>
Date:	Wed, 14 Oct 2015 10:43:28 +0200
From:	Joerg Roedel <jroedel@...e.de>
To:	Baoquan He <bhe@...hat.com>
Cc:	akpm@...ux-foundation.org, yinghai@...nel.org, dyoung@...hat.com,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, bp@...e.de,
	linux-kernel@...r.kernel.org, jerry_hoemann@...com
Subject: Re: [PATCH] Do not reserve crashkernel high memory if crashkernel
 low memory reserving failed

On Thu, Sep 24, 2015 at 11:24:51AM +0800, 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
> 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.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
> v1->v2:
>   Boris commented that error value EINVAL is negative, should
>   use "return -EINVAL".
> 
> v2->v3:
>   Yinghai pointed out that during memblock_reserve, we could double
>   the memblock reserve array. New memblock reserve could be overlapped
>   with range for crashkernel high. So we have to reserve crashkernel
>   high firstly, then free it if crashkernel low memory allocation
>   failed.
> 
> v3->v4:
>   Dave suggested using "return -ENOMEM" when low memory reservation
>   failed and printing failure message anyway.
> 
> v4->v5:
>   Andrew suggested changing the content of failure message and taking
>   higher severity KERN_ERR.
> 
>  arch/x86/kernel/setup.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)

Reviewed-by: Joerg Roedel <jroedel@...e.de>

The patch is also in SLES for some time now and was successfully tested
there.


	Joerg

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