msize.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Malloc small size classes.
     6  //
     7  // See malloc.go for overview.
     8  // See also mksizeclasses.go for how we decide what size classes to use.
     9  
    10  package runtime
    11  
    12  import "internal/runtime/gc"
    13  
    14  // Returns size of the memory block that mallocgc will allocate if you ask for the size,
    15  // minus any inline space for metadata.
    16  func roundupsize(size uintptr, noscan bool) (reqSize uintptr) {
    17  	reqSize = size
    18  	if reqSize <= maxSmallSize-gc.MallocHeaderSize {
    19  		// Small object.
    20  		if !noscan && reqSize > gc.MinSizeForMallocHeader { // !noscan && !heapBitsInSpan(reqSize)
    21  			reqSize += gc.MallocHeaderSize
    22  		}
    23  		// (reqSize - size) is either mallocHeaderSize or 0. We need to subtract mallocHeaderSize
    24  		// from the result if we have one, since mallocgc will add it back in.
    25  		if reqSize <= gc.SmallSizeMax-8 {
    26  			return uintptr(gc.SizeClassToSize[gc.SizeToSizeClass8[divRoundUp(reqSize, gc.SmallSizeDiv)]]) - (reqSize - size)
    27  		}
    28  		return uintptr(gc.SizeClassToSize[gc.SizeToSizeClass128[divRoundUp(reqSize-gc.SmallSizeMax, gc.LargeSizeDiv)]]) - (reqSize - size)
    29  	}
    30  	// Large object. Align reqSize up to the next page. Check for overflow.
    31  	reqSize += pageSize - 1
    32  	if reqSize < size {
    33  		return size
    34  	}
    35  	return reqSize &^ (pageSize - 1)
    36  }
    37
View as plain text