runtime: add arenaBaseOffset on aix/ppc64

On AIX, addresses returned by mmap are between 0x0a00000000000000
and 0x0afffffffffffff. The previous solution to handle these large
addresses was to increase the arena size up to 60 bits addresses,
cf CL 138736.

However, with the new page allocator, the 60bit heap addresses are
causing huge memory allocations, especially by (s *pageAlloc).init. mmap
and munmap syscalls dealing with these allocations are reducing
performances of every Go programs.

In order to avoid these allocations, arenaBaseOffset is set to
0x0a00000000000000 and heap addresses are on 48bit, as others operating
systems.

Updates: #35451

Change-Id: Ice916b8578f76703428ec12a82024147a7592bc0
Reviewed-on: https://go-review.googlesource.com/c/go/+/206841
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index 1db465673c..47cefa1f3b 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -831,9 +831,13 @@ func FreePageAlloc(pp *PageAlloc) {
 // 64 bit and 32 bit platforms, allowing the tests to share code
 // between the two.
 //
+// On AIX, the arenaBaseOffset is 0x0a00000000000000. However, this
+// constant can't be used here because it is negative and will cause
+// a constant overflow.
+//
 // This should not be higher than 0x100*pallocChunkBytes to support
 // mips and mipsle, which only have 31-bit address spaces.
-var BaseChunkIdx = ChunkIdx(chunkIndex((0xc000*pageAlloc64Bit + 0x100*pageAlloc32Bit) * pallocChunkBytes))
+var BaseChunkIdx = ChunkIdx(chunkIndex(((0xc000*pageAlloc64Bit + 0x100*pageAlloc32Bit) * pallocChunkBytes) + 0x0a00000000000000*sys.GoosAix))
 
 // PageBase returns an address given a chunk index and a page index
 // relative to that chunk.