[PATCH] 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_SZIE 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 | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 75df62f..a46c7d4 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1100,6 +1100,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 	p4d_t *p4dp;
 	pud_t *pudp;
 	pmd_t *pmdp;
+	int ret = 0;
 
 	do {
 		next = pmd_addr_end(addr, end);
@@ -1121,15 +1122,23 @@ 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) {
+#ifdef CONFIG_MEMORY_HOTPLUG
+				vmemmap_free(start, end, altmap);
+#endif
+				ret = -ENOMEM;
+				break;
+			}
 
 			pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
 		} else
 			vmemmap_verify((pte_t *)pmdp, node, addr, next);
 	} while (addr = next, addr != end);
 
-	return 0;
+	if (ret)
+		return vmemmap_populate_basepages(start, end, node, altmap);
+	else
+		return ret;
 }
 #endif	/* !ARM64_SWAPPER_USES_SECTION_MAPS */
 void vmemmap_free(unsigned long start, unsigned long end,
-- 
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