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 <sudaraja@codeaurora.org>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/d6c06f2ef39bbe6c715b2f6db76eb16155fdcee6.1602722808.git.sudaraja@codeaurora.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 1c0f3e02f731edd8b962b2d62a8954236b91c3d7..a773d2a1a2bf063cdafc40030cf73b00bc57ca71 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1132,8 +1132,11 @@ 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