[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 <sudar...@codeaurora.org>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Will Deacon <w...@kernel.org>
Cc: Anshuman Khandual <anshuman.khand...@arm.com>
Cc: Mark Rutland <mark.rutl...@arm.com>
Cc: Logan Gunthorpe <log...@deltatee.com>
Cc: David Hildenbrand <da...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Steven Price <steven.pr...@arm.com>
---
 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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