linux-kernel - Re: [PATCH v3 2/2] arm64: kdump: Support crashkernel=X fall back to reserve region above DMA zones

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Message-ID: <6b20a203-6aab-2b87-9b95-814aeb79b5bd@huawei.com>
Date:   Tue, 8 Nov 2022 10:06:38 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Jonathan Corbet <corbet@....net>, <linux-doc@...r.kernel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>,
        John Donnelly <John.p.donnelly@...cle.com>,
        "Dave Kleikamp" <dave.kleikamp@...cle.com>
Subject: Re: [PATCH v3 2/2] arm64: kdump: Support crashkernel=X fall back to
 reserve region above DMA zones



On 2022/11/8 1:13, Catalin Marinas wrote:
> On Mon, Jul 11, 2022 at 05:03:19PM +0800, Zhen Lei wrote:
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 5390f361208ccf7..8539598f9e58b4d 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -138,6 +138,7 @@ static void __init reserve_crashkernel(void)
>>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>  	char *cmdline = boot_command_line;
>>  	int ret;
>> +	bool fixed_base;
>>  
>>  	if (!IS_ENABLED(CONFIG_KEXEC_CORE))
>>  		return;
>> @@ -166,15 +167,28 @@ static void __init reserve_crashkernel(void)
>>  		return;
>>  	}
>>  
>> +	fixed_base = !!crash_base;
>>  	crash_size = PAGE_ALIGN(crash_size);
>>  
>>  	/* User specifies base address explicitly. */
>> -	if (crash_base)
>> +	if (fixed_base)
>>  		crash_max = crash_base + crash_size;
> 
> Not a fan of '!!', it is converted automatically. If you don't like the
> conversion, just initialise fixed_base to false and here:
> 
> 	if (crash_base) {
> 		fixed_base = true;

OK, This way would be better.

> 		crash_max = crash_base + crash_size;
> 	}
> 
>> +retry:
>>  	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>>  					       crash_base, crash_max);
>>  	if (!crash_base) {
>> +		/*
>> +		 * Attempt to fully allocate low memory failed, fall back
>> +		 * to high memory, the minimum required low memory will be
>> +		 * reserved later.
>> +		 */
> 
> I'm not sure this comment makes sense. If !crash_base, it doesn't mean
> the kernel failed to fully allocate low memory. crash_max here could be
> CRASH_ADDR_HIGH_MAX if crashkerne=X,high was specified. Maybe says
> something like "If the first attempt was for low memory, fall back to
> high ..."

This description is accurate. I'll update. Thanks.

> 
>> +		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
>> +			crash_max = CRASH_ADDR_HIGH_MAX;
>> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +			goto retry;
>> +		}
> 
> The retry logic looks fine, it only happens once as crash_max is
> updated.
> 

-- 
Regards,
  Zhen Lei