diff mbox series

[v2] arm64/mm: add fallback option to allocate virtually contiguous memory

Message ID a2d91c1b5874a1217e473ffd33cd4f765a0e78b7.1601506266.git.sudaraja@codeaurora.org
State New, archived
Headers show
Series [v2] arm64/mm: add fallback option to allocate virtually contiguous memory | expand

Commit Message

Sudarshan Rajagopalan Sept. 30, 2020, 11:13 p.m. UTC
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 | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

Comments

Anshuman Khandual Oct. 1, 2020, 12:30 a.m. UTC | #1
On 10/01/2020 04:43 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 | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 75df62f..9edbbb8 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1121,8 +1121,18 @@ 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 (altmap)
> +					return -ENOMEM;	/* no fallback */

Why ? If huge pages inside a vmemmap section might have been allocated
from altmap, the base page could also fallback on altmap. If this patch
has just followed the existing x86 semantics, it was written [1] long
back before vmemmap_populate_basepages() supported altmap allocation.
While adding that support [2] recently, it was deliberate not to change 
x86 semantics as it was a platform decision. Nonetheless, it makes sense
to fallback on altmap bases pages if and when required.

[1] 4b94ffdc4163 (x86, mm: introduce vmem_altmap to augment vmemmap_populate())
[2] 1d9cfee7535c (mm/sparsemem: enable vmem_altmap support in vmemmap_populate_basepages())
Sudarshan Rajagopalan Oct. 1, 2020, 7:51 p.m. UTC | #2
On 2020-09-30 17:30, Anshuman Khandual wrote:
> On 10/01/2020 04:43 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 | 14 ++++++++++++--
>>  1 file changed, 12 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 75df62f..9edbbb8 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1121,8 +1121,18 @@ 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 (altmap)
>> +					return -ENOMEM;	/* no fallback */
> 
> Why ? If huge pages inside a vmemmap section might have been allocated
> from altmap, the base page could also fallback on altmap. If this patch
> has just followed the existing x86 semantics, it was written [1] long
> back before vmemmap_populate_basepages() supported altmap allocation.
> While adding that support [2] recently, it was deliberate not to change
> x86 semantics as it was a platform decision. Nonetheless, it makes 
> sense
> to fallback on altmap bases pages if and when required.
> 
> [1] 4b94ffdc4163 (x86, mm: introduce vmem_altmap to augment 
> vmemmap_populate())
> [2] 1d9cfee7535c (mm/sparsemem: enable vmem_altmap support in
> vmemmap_populate_basepages())

Yes agreed. We can allow fallback on altmap as well. I did indeed follow 
x86 semantics. Will send the updated patch.

Sudarshan

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

Patch

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 75df62f..9edbbb8 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1121,8 +1121,18 @@  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 (altmap)
+					return -ENOMEM;	/* no fallback */
+
+				/*
+				 * 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