Re: [PATCH] mm: disable kernelcore=mirror when no mirror memory

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2023/7/29 16:12, Mike Rapoport wrote:
> On Fri, Jul 28, 2023 at 12:01:24PM +0800, Wupeng Ma wrote:
>> From: Ma Wupeng <mawupeng1@huawei.com>
>>
>> For system with kernelcore=mirror enabled while no mirrored memory is
>> reported by efi. This could lead to kernel OOM during startup since
>> all memory beside zone DMA are in the movable zone and this prevents
>> the kernel to use it.
>>
>> Zone DMA/DMA32 initialization is independent of mirrored memory and
>> their max pfn is set in zone_sizes_init(). Since kernel can fallback
>> to zone DMA/DMA32 if there is no memory in zone Normal, these zones
>> are seen as mirrored memory no mather their memory attributes are.
> 
> Using kernelcore= and movablecore= always come with the risk there will be
> to little memory for the kernel to use. Even if EFI reports mirrored memory
> it's possible to have OOM with kernelcore=mirror because there could be
> just not enough mirrored memory.

Yes, this is a big problem, could we add an option to move some
ZONE_MOVABLE pages into ZONE_NORMAL(MIGRATE_MOVABLE) when low free
memory?>
>> To solve this problem, disable kernelcore=mirror when there is no real
>> mirrored memory exists.
>>
>> Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
>> ---
>>   mm/internal.h | 2 ++
>>   mm/memblock.c | 2 +-
>>   mm/mm_init.c  | 6 +++++-
>>   3 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/internal.h b/mm/internal.h
>> index a7d9e980429a..98a03ac74ca7 100644
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -374,6 +374,8 @@ static inline void clear_zone_contiguous(struct zone *zone)
>>   	zone->contiguous = false;
>>   }
>>   
>> +extern bool system_has_some_mirror;
>> +
>>   extern int __isolate_free_page(struct page *page, unsigned int order);
>>   extern void __putback_isolated_page(struct page *page, unsigned int order,
>>   				    int mt);
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index f9e61e565a53..e7a7a65415fb 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -156,10 +156,10 @@ static __refdata struct memblock_type *memblock_memory = &memblock.memory;
>>   	} while (0)
>>   
>>   static int memblock_debug __initdata_memblock;
>> -static bool system_has_some_mirror __initdata_memblock;
>>   static int memblock_can_resize __initdata_memblock;
>>   static int memblock_memory_in_slab __initdata_memblock;
>>   static int memblock_reserved_in_slab __initdata_memblock;
>> +bool system_has_some_mirror __initdata_memblock;
>>   
>>   static enum memblock_flags __init_memblock choose_memblock_flags(void)
>>   {
>> diff --git a/mm/mm_init.c b/mm/mm_init.c
>> index a1963c3322af..6267b9f75927 100644
>> --- a/mm/mm_init.c
>> +++ b/mm/mm_init.c
>> @@ -269,7 +269,11 @@ static int __init cmdline_parse_kernelcore(char *p)
>>   {
>>   	/* parse kernelcore=mirror */
>>   	if (parse_option_str(p, "mirror")) {
>> -		mirrored_kernelcore = true;
>> +		if (system_has_some_mirror)
>> +			mirrored_kernelcore = true;
> 
> On many architectures early parameters are parsed before memblock is setup,
> so system_has_some_mirror will always be true.

Only x86/arm64 support kernelcore=mirror, system_has_some_mirror is
false by default, so it should no issue for now, but it is better to
move this check into find_zone_movable_pfns_for_nodes().

> 
>> +		else
>> +			pr_warn("The system has no mirror memory, disable kernelcore=mirror.\n");
>> +
>>   		return 0;
>>   	}
>>   
>> -- 
>> 2.25.1
>>
>