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

Leizhen (ThunderTown)
2022-11-08T02:06:46Z

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