runtime: prepare for 8K pages

Ensure than heap is PageSize aligned.

LGTM=iant
R=iant, dave, gobot
CC=golang-codereviews
https://golang.org/cl/56630043

diff --git a/src/pkg/runtime/malloc.goc b/src/pkg/runtime/malloc.goc
index b00d690aad8ce3fefc17931e93224a9e2c82199c..a593da486cf140660dbe224e63d21c87334fc719 100644 (file)
--- a/src/pkg/runtime/malloc.goc
+++ b/src/pkg/runtime/malloc.goc
@@ -427,7 +427,6 @@ runtime·mallocinit(void)
        byte *p;
        uintptr arena_size, bitmap_size, spans_size;
        extern byte end[];
-       byte *want;
        uintptr limit;
        uint64 i;
 
@@ -486,7 +485,7 @@ runtime·mallocinit(void)
                spans_size = ROUND(spans_size, PageSize);
                for(i = 0; i <= 0x7f; i++) {
                        p = (void*)(i<<40 | 0x00c0ULL<<32);
-                       p = runtime·SysReserve(p, bitmap_size + spans_size + arena_size);
+                       p = runtime·SysReserve(p, bitmap_size + spans_size + arena_size + PageSize);
                        if(p != nil)
                                break;
                }
@@ -528,16 +527,16 @@ runtime·mallocinit(void)
                // So adjust it upward a little bit ourselves: 1/4 MB to get
                // away from the running binary image and then round up
                // to a MB boundary.
-               want = (byte*)ROUND((uintptr)end + (1<<18), 1<<20);
-               p = runtime·SysReserve(want, bitmap_size + spans_size + arena_size);
+               p = (byte*)ROUND((uintptr)end + (1<<18), 1<<20);
+               p = runtime·SysReserve(p, bitmap_size + spans_size + arena_size + PageSize);
                if(p == nil)
                        runtime·throw("runtime: cannot reserve arena virtual address space");
-               if((uintptr)p & (((uintptr)1<<PageShift)-1))
-                       runtime·printf("runtime: SysReserve returned unaligned address %p; asked for %p", p,
-                               bitmap_size+spans_size+arena_size);
        }
-       if((uintptr)p & (((uintptr)1<<PageShift)-1))
-               runtime·throw("runtime: SysReserve returned unaligned address");
+
+       // PageSize can be larger than OS definition of page size,
+       // so SysReserve can give us a PageSize-unaligned pointer.
+       // To overcome this we ask for PageSize more and round up the pointer.
+       p = (byte*)ROUND((uintptr)p, PageSize);
 
        runtime·mheap.spans = (MSpan**)p;
        runtime·mheap.bitmap = p + spans_size;