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

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]>

Reviewed-by Gavin Shan <[email protected]>

Reviewed-by Anshuman Khandual <[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 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Quoted 20 lines · 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 <[email protected]>

Reviewed-by Gavin Shan <[email protected]>

Reviewed-by Anshuman Khandual <[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]>

Quoted 3 lines

---
 arch/arm64/mm/mmu.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Please can you fix the subject? I have three copies of "PATCH v3" from different days in my inbox. I know it sounds trivial, but getting these little things right really helps with review, especially when it's sitting amongst a sea of other patches.

Thanks,

Will

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]>

Reviewed-by Gavin Shan <[email protected]>

Reviewed-by Anshuman Khandual <[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 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

arch/arm64/mm/mmu.c +5 -2

index 75df62fea1b6..44486fd0e883 100644
@@ -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

Did you have a chance to review this patch? It is reviewed by others and haven't seen any Nacks. This patch will be useful to have so that memory hotremove doesn't fail when such PMD_SIZE pages aren't available.. which is usually the case in low RAM devices.

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]>

Reviewed-by Gavin Shan <[email protected]>

Reviewed-by Anshuman Khandual <[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 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

arch/arm64/mm/mmu.c +0 -0

index 75df62fea1b6..44486fd0e883 100644

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 continous to allocate physically contiguous memory for other sections.
https://lkml.org/lkml/2020/9/30/1489

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