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

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Date:   Mon, 10 Apr 2023 17:52:37 +0800
From:   "chenjiahao (C)" <chenjiahao16@...wei.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>,
        Simon Horman <horms@...nel.org>
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>
Subject: Re: [PATCH -next v3 1/2] riscv: kdump: Implement
 crashkernel=X,[high,low]


On 2023/4/8 10:00, Leizhen (ThunderTown) wrote:
>
> On 2023/4/7 20:58, Leizhen (ThunderTown) wrote:
>>
>> On 2023/4/7 20:03, Simon Horman wrote:
>>> 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] */
>> The description "crashkernel=X,[high,low] can be specified or not" is not
>> correct, because crashkernel=X,high must be specified when walking into this
>> branch. So use Simon's comments or copy arm64's comments(it's written for
>> parse_crashkernel_low()).
> I rethink it a little bit, if it's relative to crashkernel=X[@offset],
> that's also true.
>
> Reviewed-by: Zhen Lei <thunder.leizhen@...wei.com>

Sure, The commit should not be ambiguous like this, Simon's comment above is

a better option.


>>>
>>>> +		 */
>>>> +		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/
>> Seems like the whole "and high memory is reserved successful" needs to be deleted.
>> Only the dependency between the two boot options should be described here,
>> regardless of whether their memory is successfully allocated.

The comment here is imprecise, since there is absolutely no check whether

the allocation is successful before "parse_crashkernel_low"


>>
>>>> +		 */
>>>> +		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;
>>>> +	}
>>> ...
>>> .
>>>
BR,

Jiahao