runtime: use 4 MiB heap arenas on iOS

iOS arm64 is a 64-bit platform but with a strictly 32-bit address space
(technically 33 bits, but the bottom half is unavailable to the
application). Since address space is limited, use 4 MiB arenas instead
of 64 MiB arenas. No changes are needed to the arena index because it's
still relatively small; this change just brings iOS more in line with
32-bit platforms.

Change-Id: I484e2d273d896fd0a57cd5c25012df0aef160290
Reviewed-on: https://go-review.googlesource.com/c/go/+/270538
Trust: Michael Knyszek <mknyszek@google.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index 5e4974d40e77a592373af7a01bf227753e1739ea..f2d2425f53e54c31e14f6b0152d1cf9c0378a235 100644 (file)
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -227,6 +227,7 @@ const (
        // --------------  ---------  ----------  ----------  -----------
        //       */64-bit         48        64MB           1    4M (32MB)
        // windows/64-bit         48         4MB          64    1M  (8MB)
+       //      ios/arm64         33         4MB           1  2048  (8KB)
        //       */32-bit         32         4MB           1  1024  (4KB)
        //     */mips(le)         31         4MB           1   512  (2KB)
 
@@ -247,7 +248,7 @@ const (
        // logHeapArenaBytes is log_2 of heapArenaBytes. For clarity,
        // prefer using heapArenaBytes where possible (we need the
        // constant to compute some other constants).
-       logHeapArenaBytes = (6+20)*(_64bit*(1-sys.GoosWindows)*(1-sys.GoarchWasm)) + (2+20)*(_64bit*sys.GoosWindows) + (2+20)*(1-_64bit) + (2+20)*sys.GoarchWasm
+       logHeapArenaBytes = (6+20)*(_64bit*(1-sys.GoosWindows)*(1-sys.GoarchWasm)*(1-sys.GoosIos*sys.GoarchArm64)) + (2+20)*(_64bit*sys.GoosWindows) + (2+20)*(1-_64bit) + (2+20)*sys.GoarchWasm + (2+20)*sys.GoosIos*sys.GoarchArm64
 
        // heapArenaBitmapBytes is the size of each heap arena's bitmap.
        heapArenaBitmapBytes = heapArenaBytes / (sys.PtrSize * 8 / 2)