[PATCH v3] arm64/mm: add fallback option to allocate virtually

[PATCH v3] arm64/mm: add fallback option to allocate virtually

[Sudarshan Rajagopalan]

V1: The initial patch used the approach to abort at the first instance of PMD_SIZE
allocation failure, unmaps all previously mapped sections using vmemmap_free
and maps the entire request with vmemmap_populate_basepages to allocate
virtually contiguous memory.
https://lkml.org/lkml/2020/9/10/66

V2: Allocates virtually contiguous memory only for sections that failed
PMD_SIZE allocation, and continues to allocate physically contiguous
memory for other sections.
https://lkml.org/lkml/2020/9/30/1489

V3: Addresses Anshuman's comment to allow fallback to altmap base pages
as well if and when required.

Sudarshan Rajagopalan (1):
  arm64/mm: add fallback option to allocate virtually contiguous memory

 arch/arm64/mm/mmu.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

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

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

[Sudarshan Rajagopalan]

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().

Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Price <steven.price@arm.com>
---
 arch/arm64/mm/mmu.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 75df62f..11f8639 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1121,8 +1121,15 @@ 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) {
+				/*
+				 * fallback allocating with virtually
+				 * contiguous memory for this section
+				 */
+				if (vmemmap_populate_basepages(addr, next, node, NULL))
+					return -ENOMEM;
+				continue;
+			}
 
 			pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
 		} else
-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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

[Anshuman Khandual]

On 10/02/2020 01:46 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().
> 
> Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Steven Price <steven.price@arm.com>
> ---
>  arch/arm64/mm/mmu.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 75df62f..11f8639 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1121,8 +1121,15 @@ 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) {
> +				/*
> +				 * fallback allocating with virtually
> +				 * contiguous memory for this section
> +				 */

Mapping is always virtually contiguous with or without huge pages.
Please drop this comment here, as it's obvious.

> +				if (vmemmap_populate_basepages(addr, next, node, NULL))
> +					return -ENOMEM;

Please send in the 'altmap' instead of NULL for allocation from
device memory if and when requested.

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

[Gavin Shan]

On 10/6/20 2:36 PM, Anshuman Khandual wrote:
> On 10/02/2020 01:46 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().
>>
>> Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Logan Gunthorpe <logang@deltatee.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Steven Price <steven.price@arm.com>
>> ---
>>   arch/arm64/mm/mmu.c | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>

It looks good to me with Anshuman's comments fixed:

Reviewed-by: Gavin Shan <gshan@redhat.com>

>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 75df62f..11f8639 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1121,8 +1121,15 @@ 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) {
>> +				/*
>> +				 * fallback allocating with virtually
>> +				 * contiguous memory for this section
>> +				 */
> 
> Mapping is always virtually contiguous with or without huge pages.
> Please drop this comment here, as it's obvious.
> 
>> +				if (vmemmap_populate_basepages(addr, next, node, NULL))
>> +					return -ENOMEM;
> 
> Please send in the 'altmap' instead of NULL for allocation from
> device memory if and when requested.
> 
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