malloc in runtime (not used by default)

R=r
DELTA=1551  (1550 added, 0 deleted, 1 changed)
OCL=21404
CL=21538

1 files changed, 164 insertions, 0 deletions

diff --git a/src/runtime/msize.c b/src/runtime/msize.c
new file mode 100644
index 000000000..84de243f6
--- /dev/null
+++ b/src/runtime/msize.c
@@ -0,0 +1,164 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Malloc small size classes.
+//
+// See malloc.h for overview.
+//
+// The size classes are chosen so that rounding an allocation
+// request up to the next size class wastes at most 12.5% (1.125x).
+//
+// Each size class has its own page count that gets allocated
+// and chopped up when new objects of the size class are needed.
+// That page count is chosen so that chopping up the run of
+// pages into objects of the given size wastes at most 12.5% (1.125x)
+// of the memory.  It is not necessary that the cutoff here be
+// the same as above.
+//
+// The two sources of waste multiply, so the worst possible case
+// for the above constraints would be that allocations of some
+// size might have a 26.6% (1.266x) overhead.
+// In practice, only one of the wastes comes into play for a
+// given size (sizes < 512 waste mainly on the round-up,
+// sizes > 512 waste mainly on the page chopping).
+//
+// TODO(rsc): Compute max waste for any given size.
+
+#include "runtime.h"
+#include "malloc.h"
+
+int32 class_to_size[NumSizeClasses];
+int32 class_to_allocnpages[NumSizeClasses];
+int32 class_to_transfercount[NumSizeClasses];
+
+// The SizeToClass lookup is implemented using two arrays,
+// one mapping sizes <= 1024 to their class and one mapping
+// sizes >= 1024 and <= MaxSmallSize to their class.
+// All objects are 8-aligned, so the first array is indexed by
+// the size divided by 8 (rounded up).  Objects >= 1024 bytes
+// are 128-aligned, so the second array is indexed by the
+// size divided by 128 (rounded up).  The arrays are filled in
+// by InitSizes.
+
+static int32 size_to_class8[1024/8 + 1];
+static int32 size_to_class128[(MaxSmallSize-1024)/128 + 1];
+
+int32
+SizeToClass(int32 size)
+{
+	if(size > MaxSmallSize)
+		throw("SizeToClass - invalid size");
+	if(size > 1024-8)
+		return size_to_class128[(size-1024+127) >> 7];
+	return size_to_class8[(size+7)>>3];
+}
+
+void
+InitSizes(void)
+{
+	int32 align, sizeclass, size, i, nextsize, n;
+	uintptr allocsize, npages;
+
+	// Initialize the class_to_size table (and choose class sizes in the process).
+	class_to_size[0] = 0;
+	sizeclass = 1;	// 0 means no class
+	align = 8;
+	for(size = align; size <= MaxSmallSize; size += align) {
+		if((size&(size-1)) == 0) {	// bump alignment once in a while
+			if(size >= 2048)
+				align = 256;
+			else if(size >= 128)
+				align = size / 8;
+			else if(size >= 16)
+				align = 16;	// required for x86 SSE instructions, if we want to use them
+		}
+		if((align&(align-1)) != 0)
+			throw("InitSizes - bug");
+
+		// Make the allocnpages big enough that
+		// the leftover is less than 1/8 of the total,
+		// so wasted space is at most 12.5%.
+		allocsize = PageSize;
+		while(allocsize%size > (PageSize/8))
+			allocsize += PageSize;
+		npages = allocsize >> PageShift;
+
+		// If the previous sizeclass chose the same
+		// allocation size and fit the same number of
+		// objects into the page, we might as well
+		// use just this size instead of having two
+		// different sizes.
+		if(sizeclass > 1
+		&& npages == class_to_allocnpages[sizeclass-1]
+		&& allocsize/size == allocsize/class_to_size[sizeclass-1]) {
+			class_to_size[sizeclass-1] = size;
+			continue;
+		}
+
+		class_to_allocnpages[sizeclass] = npages;
+		class_to_size[sizeclass] = size;
+		sizeclass++;
+	}
+	if(sizeclass != NumSizeClasses) {
+		printf("sizeclass=%d NumSizeClasses=%d\n", sizeclass, NumSizeClasses);
+		throw("InitSizes - bad NumSizeClasses");
+	}
+
+	// Initialize the size_to_class tables.
+	nextsize = 0;
+	for (sizeclass = 1; sizeclass < NumSizeClasses; sizeclass++) {
+		for(; nextsize < 1024 && nextsize <= class_to_size[sizeclass]; nextsize+=8)
+			size_to_class8[nextsize/8] = sizeclass;
+		if(nextsize >= 1024)
+			for(; nextsize <= class_to_size[sizeclass]; nextsize += 128)
+				size_to_class128[(nextsize-1024)/128] = sizeclass;
+	}
+
+	// Double-check SizeToClass.
+	if(0) {
+		for(n=0; n < MaxSmallSize; n++) {
+			sizeclass = SizeToClass(n);
+			if(sizeclass < 1 || sizeclass >= NumSizeClasses || class_to_size[sizeclass] < n) {
+				printf("size=%d sizeclass=%d class_to_size=%d\n", n, sizeclass, class_to_size[sizeclass]);
+				printf("incorrect SizeToClass");
+				goto dump;
+			}
+			if(sizeclass > 1 && class_to_size[sizeclass-1] >= n) {
+				printf("size=%d sizeclass=%d class_to_size=%d\n", n, sizeclass, class_to_size[sizeclass]);
+				printf("SizeToClass too big");
+				goto dump;
+			}
+		}
+	}
+
+	// Initialize the class_to_transfercount table.
+	for(sizeclass = 1; sizeclass < NumSizeClasses; sizeclass++) {
+		n = 64*1024 / class_to_size[sizeclass];
+		if(n < 2)
+			n = 2;
+		if(n > 32)
+			n = 32;
+		class_to_transfercount[sizeclass] = n;
+	}
+	return;
+
+dump:
+	if(1){
+		printf("NumSizeClasses=%d\n", NumSizeClasses);
+		printf("class_to_size:");
+		for(sizeclass=0; sizeclass<NumSizeClasses; sizeclass++)
+			printf(" %d", class_to_size[sizeclass]);
+		printf("\n\n");
+		printf("size_to_class8:");
+		for(i=0; i<nelem(size_to_class8); i++)
+			printf(" %d=>%d(%d)\n", i*8, size_to_class8[i], class_to_size[size_to_class8[i]]);
+		printf("\n");
+		printf("size_to_class128:");
+		for(i=0; i<nelem(size_to_class128); i++)
+			printf(" %d=>%d(%d)\n", i*128, size_to_class128[i], class_to_size[size_to_class128[i]]);
+		printf("\n");
+	}
+	throw("InitSizes failed");
+}
+