Subject: Re: [PATCH v3] arm64/mm: add fallback option to allocate virtually contiguous memory

From: Sudarshan Rajagopalan <[email-masked]>
Date: Wed, 14 Oct 2020 17:54:16 -0700

On 2020-10-13 04:38, Anshuman Khandual wrote:
> On 10/13/2020 04:35 AM, Sudarshan Rajagopalan wrote:
>> When section mappings are enabled, we allocate vmemmap pages from 
>> physically
>> continuous memory of size PMD_SIZE using vmemmap_alloc_block_buf(). 
>> Section
>> mappings are good to reduce TLB pressure. But when system is highly 
>> fragmented
>> and memory blocks are being hot-added at runtime, its possible that 
>> such
>> physically continuous memory allocations can fail. Rather than failing 
>> the
>> memory hot-add procedure, add a fallback option to allocate vmemmap 
>> pages from
>> discontinuous pages using vmemmap_populate_basepages().
> 
> There is a checkpatch warning here, which could be fixed while merging 
> ?
> 
> WARNING: Possible unwrapped commit description (prefer a maximum 75
> chars per line)
> #7:
> When section mappings are enabled, we allocate vmemmap pages from 
> physically
> 
> total: 0 errors, 1 warnings, 13 lines checked
> 

Thanks Anshuman for the review. I sent out an updated patch fixing the 
checkpatch warning.

>> 
>> Signed-off-by: Sudarshan Rajagopalan <[email-masked]>
>> Reviewed-by: Gavin Shan <[email-masked]>
>> Cc: Catalin Marinas <[email-masked]>
>> Cc: Will Deacon <[email-masked]>
>> Cc: Anshuman Khandual <[email-masked]>
>> Cc: Mark Rutland <[email-masked]>
>> Cc: Logan Gunthorpe <[email-masked]>
>> Cc: David Hildenbrand <[email-masked]>
>> Cc: Andrew Morton <[email-masked]>
>> Cc: Steven Price <[email-masked]>
> 
> Nonetheless, this looks fine. Did not see any particular problem
> while creating an experimental vmemmap with interleaving section
> and base page mapping.
> 
> Reviewed-by: Anshuman Khandual <[email-masked]>
> 
>> ---
>>  arch/arm64/mm/mmu.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 75df62fea1b6..44486fd0e883 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1121,8 +1121,11 @@ int __meminit vmemmap_populate(unsigned long 
>> start, unsigned long end, int node,
>>  			void *p = NULL;
>> 
>>  			p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
>> -			if (!p)
>> -				return -ENOMEM;
>> +			if (!p) {
>> +				if (vmemmap_populate_basepages(addr, next, node, altmap))
>> +					return -ENOMEM;
>> +				continue;
>> +			}
>> 
>>  			pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
>>  		} else
>> 

Sudarshan

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
Linux Foundation Collaborative Project

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