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

Sudarshan Rajagopalan sudaraja at codeaurora.org
Wed Sep 30 19:13:25 EDT 2020

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 at codeaurora.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Anshuman Khandual <anshuman.khandual at arm.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Logan Gunthorpe <logang at deltatee.com>
Cc: David Hildenbrand <david at redhat.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Steven Price <steven.price at 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 */
+				/*
+				 * 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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