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.
Sudarshan Rajagopalan (1):
arm64/mm: add fallback option to allocate virtually contiguous memory
arch/arm64/mm/mmu.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
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 <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Logan Gunthorpe <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Steven Price <[email protected]>
---
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 */
+
+ /*
+ * 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
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 <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Anshuman Khandual <[email protected]>
> Cc: Mark Rutland <[email protected]>
> Cc: Logan Gunthorpe <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Steven Price <[email protected]>
> ---
> 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())
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 <[email protected]>
>> Cc: Catalin Marinas <[email protected]>
>> Cc: Will Deacon <[email protected]>
>> Cc: Anshuman Khandual <[email protected]>
>> Cc: Mark Rutland <[email protected]>
>> Cc: Logan Gunthorpe <[email protected]>
>> Cc: David Hildenbrand <[email protected]>
>> Cc: Andrew Morton <[email protected]>
>> Cc: Steven Price <[email protected]>
>> ---
>> 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
--
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Linux Foundation Collaborative Project