InnoDB fails to start up with CONFIG_ARM64_VA_BITS_39=y

MDEV-38671 changed the default value of the parameter innodb_buffer_pool_size_max to 8 TiB (8 << 40 or 1 << 43 or 2⁴³ bytes) on 64-bit systems.

The assumption was that on every 64-bit system, the size of the virtual address space would be close to 48 bits. However, on ARMv8, the Linux kernel can be configured with a 39-bit virtual address space (512 GiB). In such environments, we should limit the default innodb_buffer_pool_size_max to 256 GiB.

Note: This is independent of MDEV-39139, which is about RLIMIT_AS.

It is yet to be determined how this configuration can be best detected from the user space. Perhaps simply like this:

diff --git a/storage/innobase/buf/buf0buf.cc b/storage/innobase/buf/buf0buf.cc

index cb264e788e9..877350ec6cd 100644

--- a/storage/innobase/buf/buf0buf.cc

+++ b/storage/innobase/buf/buf0buf.cc

@@ -1343,7 +1343,16 @@ bool buf_pool_t::create() noexcept

 #endif

   }

-  if (!memory_unaligned)

+  if (memory_unaligned);

+#ifdef __aarch64__

+  else if (size_in_bytes_max == innodb_buffer_pool_size_max_default)

+  {

+    /* Accommodate CONFIG_ARM64_VA_BITS_39 */

+    size_in_bytes_max= 1 << 37; /* a quarter of the available address space */

+    goto init;

+  }

+#endif

+  else

     goto oom;

   const size_t alignment_waste=

We may need a similar adjustment for other platforms where the virtual address space may be narrower than 44 bits (16 TiB).