linux-kernel - Re: [PATCH -next v3 1/2] riscv: kdump: Implement crashkernel=X,[high,low]

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Date:   Fri, 7 Apr 2023 14:03:23 +0200
From:   Simon Horman <horms@...nel.org>
To:     Chen Jiahao <chenjiahao16@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        kexec@...ts.infradead.org, linux-doc@...r.kernel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        conor.dooley@...rochip.com, guoren@...nel.org, heiko@...ech.de,
        bjorn@...osinc.com, alex@...ti.fr, akpm@...ux-foundation.org,
        atishp@...osinc.com, bhe@...hat.com, thunder.leizhen@...wei.com
Subject: Re: [PATCH -next v3 1/2] riscv: kdump: Implement
 crashkernel=X,[high,low]

On Fri, Apr 07, 2023 at 06:02:05AM +0800, Chen Jiahao wrote:
> On riscv, the current crash kernel allocation logic is trying to
> allocate within 32bit addressible memory region by default, if
> failed, try to allocate without 4G restriction.
> 
> In need of saving DMA zone memory while allocating a relatively large
> crash kernel region, allocating the reserved memory top down in
> high memory, without overlapping the DMA zone, is a mature solution.
> Here introduce the parameter option crashkernel=X,[high,low].
> 
> One can reserve the crash kernel from high memory above DMA zone range
> by explicitly passing "crashkernel=X,high"; or reserve a memory range
> below 4G with "crashkernel=X,low".
> 
> Signed-off-by: Chen Jiahao <chenjiahao16@...wei.com>

...

> @@ -1180,14 +1206,37 @@ static void __init reserve_crashkernel(void)
>  		return;
>  	}
>  
> -	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> +	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>  				&crash_size, &crash_base);
> -	if (ret || !crash_size)
> +	if (ret == -ENOENT) {
> +		/*
> +		 * crashkernel=X,[high,low] can be specified or not, but
> +		 * invalid value is not allowed.

nit: Perhaps something like this would be easier to correlate with the
     code that follows:

		/* Fallback to crashkernel=X,[high,low] */


> +		 */
> +		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
> +		if (ret || !crash_size)
> +			return;
> +
> +		/*
> +		 * crashkernel=Y,low is valid only when crashkernel=X,high
> +		 * is passed and high memory is reserved successful.

nit: s/successful/successfully/

> +		 */
> +		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
> +		if (ret == -ENOENT)
> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +		else if (ret)
> +			return;
> +
> +		search_start = search_low_max;
> +	} else if (ret || !crash_size) {
> +		/* Invalid argument value specified */
>  		return;
> +	}

...