libgo patch committed: Fix madvise on systems with page size != 4096

[Ian Lance Taylor]

This patch from Anton Blanchard fixes libgo to adjust to the system page
size when calling madvise.  Bootstrapped and ran Go testsuite on
x86_64-unknown-linux-gnu.  Committed to mainline and 4.9 branch.

Ian


diff -r 3a53301d24d7 libgo/runtime/mheap.c
--- a/libgo/runtime/mheap.c	Tue Apr 22 16:43:35 2014 -0700
+++ b/libgo/runtime/mheap.c	Thu Apr 24 21:18:35 2014 -0700
@@ -387,7 +387,7 @@
 static uintptr
 scavengelist(MSpan *list, uint64 now, uint64 limit)
 {
-	uintptr released, sumreleased;
+	uintptr released, sumreleased, start, end, pagesize;
 	MSpan *s;
 
 	if(runtime_MSpanList_IsEmpty(list))
@@ -400,7 +400,17 @@
 			mstats.heap_released += released;
 			sumreleased += released;
 			s->npreleased = s->npages;
-			runtime_SysUnused((void*)(s->start << PageShift), s->npages << PageShift);
+
+			start = s->start << PageShift;
+			end = start + (s->npages << PageShift);
+
+			// Round start up and end down to ensure we
+			// are acting on entire pages.
+			pagesize = getpagesize();
+			start = ROUND(start, pagesize);
+			end &= ~(pagesize - 1);
+			if(end > start)
+				runtime_SysUnused((void*)start, end - start);
 		}
 	}
 	return sumreleased;