diff options
Diffstat (limited to 'src/runtime')
| -rw-r--r-- | src/runtime/mbitmap.go | 23 | ||||
| -rw-r--r-- | src/runtime/mgcmark.go | 2 |
2 files changed, 18 insertions, 7 deletions
diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go index 2c2e8a0290..5845267b5f 100644 --- a/src/runtime/mbitmap.go +++ b/src/runtime/mbitmap.go @@ -32,12 +32,10 @@ // If ha.noMorePtrs[i]>>j&1 is set, the entries in ha.bitmap[8*i+j+1] and // beyond must all be zero until the start of the next object. // -// The bitmap for noscan spans is not maintained (can be junk). Code must -// ensure that an object is scannable before consulting its bitmap by -// checking either the noscan bit in the span or by consulting its -// type's information. +// The bitmap for noscan spans is set to all zero at span allocation time. // -// The bitmap for unallocated objects is also not maintained. +// The bitmap for unallocated objects in scannable spans is not maintained +// (can be junk). package runtime @@ -722,6 +720,16 @@ func typeBitsBulkBarrier(typ *_type, dst, src, size uintptr) { // If this is a span of single pointer allocations, it initializes all // words to pointer. func (s *mspan) initHeapBits() { + if s.spanclass.noscan() { + // Set all the pointer bits to zero. We do this once + // when the span is allocated so we don't have to do it + // for each object allocation. + base := s.base() + size := s.npages * pageSize + h := writeHeapBitsForAddr(base) + h.flush(base, size) + return + } isPtrs := goarch.PtrSize == 8 && s.elemsize == goarch.PtrSize if !isPtrs { return // nothing to do @@ -873,7 +881,7 @@ func (h writeHeapBits) flush(addr, size uintptr) { // Continue on writing zeros for the rest of the object. // For standard use of the ptr bits this is not required, as // the bits are read from the beginning of the object. Some uses, - // like oblets, bulk write barriers, and cgocheck, might + // like noscan spans, oblets, bulk write barriers, and cgocheck, might // start mid-object, so these writes are still required. for { // Write zero bits. @@ -942,7 +950,8 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) { // It's one word and it has pointers, it must be a pointer. // Since all allocated one-word objects are pointers // (non-pointers are aggregated into tinySize allocations), - // initSpan sets the pointer bits for us. Nothing to do here. + // (*mspan).initHeapBits sets the pointer bits for us. + // Nothing to do here. if doubleCheck { h, addr := heapBitsForAddr(x, size).next() if addr != x { diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go index d4d7c93ba9..c2602c0aa1 100644 --- a/src/runtime/mgcmark.go +++ b/src/runtime/mgcmark.go @@ -1273,6 +1273,8 @@ func scanobject(b uintptr, gcw *gcWork) { throw("scanobject n == 0") } if s.spanclass.noscan() { + // Correctness-wise this is ok, but it's inefficient + // if noscan objects reach here. throw("scanobject of a noscan object") } |