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

From: Sudarshan Rajagopalan
Date: Thu Oct 01 2020 - 16:19:12 EST


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@xxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Steven Price <steven.price@xxxxxxx>
---
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
--
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