src/runtime/mheap.c - go - Git at Google

 // 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.

 // Page heap.
 //
 // See malloc.h for overview.
 //
 // When a MSpan is in the heap free list, state == MSpanFree
 // and heapmap(s->start) == span, heapmap(s->start+s->npages-1) == span.
 //
 // When a MSpan is allocated, state == MSpanInUse
 // and heapmap(i) == span for all s->start <= i < s->start+s->npages.

 #include "runtime.h"
 #include "malloc.h"

 static MSpan *MHeap_AllocLocked(MHeap*, uintptr, int32);
 static bool MHeap_Grow(MHeap*, uintptr);
 static void MHeap_FreeLocked(MHeap*, MSpan*);
 static MSpan *MHeap_AllocLarge(MHeap*, uintptr);
 static MSpan *BestFit(MSpan*, uintptr, MSpan*);

 // Initialize the heap; fetch memory using alloc.
 void
 MHeap_Init(MHeap *h, void *(*alloc)(uintptr))
 {
 	uint32 i;

 	FixAlloc_Init(&h->spanalloc, sizeof(MSpan), alloc);
 	FixAlloc_Init(&h->cachealloc, sizeof(MCache), alloc);
 	MHeapMap_Init(&h->map, alloc);
 	// h->mapcache needs no init
 	for(i=0; i<nelem(h->free); i++)
 		MSpanList_Init(&h->free[i]);
 	MSpanList_Init(&h->large);
 	for(i=0; i<nelem(h->central); i++)
 		MCentral_Init(&h->central[i], i);
 }

 // Allocate a new span of npage pages from the heap
 // and record its size class in the HeapMap and HeapMapCache.
 MSpan*
 MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass)
 {
 	MSpan *s;

 	lock(h);
 	s = MHeap_AllocLocked(h, npage, sizeclass);
 	unlock(h);
 	return s;
 }

 static MSpan*
 MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
 {
 	uintptr n;
 	MSpan *s, *t;

 	// Try in fixed-size lists up to max.
 	for(n=npage; n < nelem(h->free); n++) {
 		if(!MSpanList_IsEmpty(&h->free[n])) {
 			s = h->free[n].next;
 			goto HaveSpan;
 		}
 	}

 	// Best fit in list of large spans.
 	if((s = MHeap_AllocLarge(h, npage)) == nil) {
 		if(!MHeap_Grow(h, npage))
 			return nil;
 		if((s = MHeap_AllocLarge(h, npage)) == nil)
 			return nil;
 	}

 HaveSpan:
 	// Mark span in use.
 	if(s->state != MSpanFree)
 		throw("MHeap_AllocLocked - MSpan not free");
 	if(s->npages < npage)
 		throw("MHeap_AllocLocked - bad npages");
 	MSpanList_Remove(s);
 	s->state = MSpanInUse;

 	if(s->npages > npage) {
 		// Trim extra and put it back in the heap.
 		t = FixAlloc_Alloc(&h->spanalloc);
 		MSpan_Init(t, s->start + npage, s->npages - npage);
 		s->npages = npage;
 		MHeapMap_Set(&h->map, t->start - 1, s);
 		MHeapMap_Set(&h->map, t->start, t);
 		MHeapMap_Set(&h->map, t->start + t->npages - 1, t);
 		t->state = MSpanInUse;
 		MHeap_FreeLocked(h, t);
 	}

 	// If span is being used for small objects, cache size class.
 	// No matter what, cache span info, because gc needs to be
 	// able to map interior pointer to containing span.
 	s->sizeclass = sizeclass;
 	for(n=0; n<npage; n++)
 		MHeapMap_Set(&h->map, s->start+n, s);
 	if(sizeclass == 0) {
 		uintptr tmp;

 		// If there are entries for this span, invalidate them,
 		// but don't blow out cache entries about other spans.
 		for(n=0; n<npage; n++)
 			if(MHeapMapCache_GET(&h->mapcache, s->start+n, tmp) != 0)
 				MHeapMapCache_SET(&h->mapcache, s->start+n, 0);
 	} else {
 		// Save cache entries for this span.
 		// If there's a size class, there aren't that many pages.
 		for(n=0; n<npage; n++)
 			MHeapMapCache_SET(&h->mapcache, s->start+n, sizeclass);
 	}

 	return s;
 }

 // Allocate a span of exactly npage pages from the list of large spans.
 static MSpan*
 MHeap_AllocLarge(MHeap *h, uintptr npage)
 {
 	return BestFit(&h->large, npage, nil);
 }

 // Search list for smallest span with >= npage pages.
 // If there are multiple smallest spans, take the one
 // with the earliest starting address.
 static MSpan*
 BestFit(MSpan *list, uintptr npage, MSpan *best)
 {
 	MSpan *s;

 	for(s=list->next; s != list; s=s->next) {
 		if(s->npages < npage)
 			continue;
 		if(best == nil
 		|| s->npages < best->npages
 		|| (s->npages == best->npages && s->start < best->start))
 			best = s;
 	}
 	return best;
 }

 // Try to add at least npage pages of memory to the heap,
 // returning whether it worked.
 static bool
 MHeap_Grow(MHeap *h, uintptr npage)
 {
 	uintptr ask;
 	void *v;
 	MSpan *s;

 	// Ask for a big chunk, to reduce the number of mappings
 	// the operating system needs to track; also amortizes
 	// the overhead of an operating system mapping.
 	ask = npage<<PageShift;
 	if(ask < HeapAllocChunk)
 		ask = HeapAllocChunk;

 	v = SysAlloc(ask);
 	if(v == nil) {
 		if(ask > (npage<<PageShift)) {
 			ask = npage<<PageShift;
 			v = SysAlloc(ask);
 		}
 		if(v == nil)
 			return false;
 	}

 	// NOTE(rsc): In tcmalloc, if we've accumulated enough
 	// system allocations, the heap map gets entirely allocated
 	// in 32-bit mode.  (In 64-bit mode that's not practical.)

 	if(!MHeapMap_Preallocate(&h->map, ((uintptr)v>>PageShift) - 1, (ask>>PageShift) + 2)) {
 		SysFree(v, ask);
 		return false;
 	}

 	// Create a fake "in use" span and free it, so that the
 	// right coalescing happens.
 	s = FixAlloc_Alloc(&h->spanalloc);
 	MSpan_Init(s, (uintptr)v>>PageShift, ask>>PageShift);
 	MHeapMap_Set(&h->map, s->start, s);
 	MHeapMap_Set(&h->map, s->start + s->npages - 1, s);
 	s->state = MSpanInUse;
 	MHeap_FreeLocked(h, s);
 	return true;
 }

 // Look up the span at the given page number.
 MSpan*
 MHeap_Lookup(MHeap *h, PageID p)
 {
 	return MHeapMap_Get(&h->map, p);
 }

 // Free the span back into the heap.
 void
 MHeap_Free(MHeap *h, MSpan *s)
 {
 	lock(h);
 	MHeap_FreeLocked(h, s);
 	unlock(h);
 }

 static void
 MHeap_FreeLocked(MHeap *h, MSpan *s)
 {
 	MSpan *t;

 	if(s->state != MSpanInUse || s->ref != 0) {
 		printf("MHeap_FreeLocked - span %p ptr %p state %d ref %d\n", s, s->start<<PageShift, s->state, s->ref);
 		throw("MHeap_FreeLocked - invalid free");
 	}
 	s->state = MSpanFree;
 	MSpanList_Remove(s);

 	// Coalesce with earlier, later spans.
 	if((t = MHeapMap_Get(&h->map, s->start - 1)) != nil && t->state != MSpanInUse) {
 		s->start = t->start;
 		s->npages += t->npages;
 		MHeapMap_Set(&h->map, s->start, s);
 		MSpanList_Remove(t);
 		FixAlloc_Free(&h->spanalloc, t);
 	}
 	if((t = MHeapMap_Get(&h->map, s->start + s->npages)) != nil && t->state != MSpanInUse) {
 		s->npages += t->npages;
 		MHeapMap_Set(&h->map, s->start + s->npages - 1, s);
 		MSpanList_Remove(t);
 		FixAlloc_Free(&h->spanalloc, t);
 	}

 	// Insert s into appropriate list.
 	if(s->npages < nelem(h->free))
 		MSpanList_Insert(&h->free[s->npages], s);
 	else
 		MSpanList_Insert(&h->large, s);

 	// TODO(rsc): IncrementalScavenge() to return memory to OS.
 }

 // 3-level radix tree mapping page ids to Span*.
 void
 MHeapMap_Init(MHeapMap *m, void *(*allocator)(size_t))
 {
 	m->allocator = allocator;
 }

 MSpan*
 MHeapMap_Get(MHeapMap *m, PageID k)
 {
 	int32 i1, i2, i3;

 	i3 = k & MHeapMap_Level3Mask;
 	k >>= MHeapMap_Level3Bits;
 	i2 = k & MHeapMap_Level2Mask;
 	k >>= MHeapMap_Level2Bits;
 	i1 = k & MHeapMap_Level1Mask;
 	k >>= MHeapMap_Level1Bits;
 	if(k != 0)
 		throw("MHeapMap_Get");

 	return m->p[i1]->p[i2]->s[i3];
 }

 void
 MHeapMap_Set(MHeapMap *m, PageID k, MSpan *s)
 {
 	int32 i1, i2, i3;

 	i3 = k & MHeapMap_Level3Mask;
 	k >>= MHeapMap_Level3Bits;
 	i2 = k & MHeapMap_Level2Mask;
 	k >>= MHeapMap_Level2Bits;
 	i1 = k & MHeapMap_Level1Mask;
 	k >>= MHeapMap_Level1Bits;
 	if(k != 0)
 		throw("MHeapMap_Set");

 	m->p[i1]->p[i2]->s[i3] = s;
 }

 // Allocate the storage required for entries [k, k+1, ..., k+len-1]
 // so that Get and Set calls need not check for nil pointers.
 bool
 MHeapMap_Preallocate(MHeapMap *m, PageID k, uintptr len)
 {
 	uintptr end;
 	int32 i1, i2;
 	MHeapMapNode2 *p2;
 	MHeapMapNode3 *p3;

 	end = k+len;
 	while(k < end) {
 		if((k >> MHeapMap_TotalBits) != 0)
 			return false;
 		i2 = (k >> MHeapMap_Level3Bits) & MHeapMap_Level2Mask;
 		i1 = (k >> (MHeapMap_Level3Bits + MHeapMap_Level2Bits)) & MHeapMap_Level1Mask;

 		// first-level pointer
 		if((p2 = m->p[i1]) == nil) {
 			p2 = m->allocator(sizeof *p2);
 			if(p2 == nil)
 				return false;
 			sys_memclr((byte*)p2, sizeof *p2);
 			m->p[i1] = p2;
 		}

 		// second-level pointer
 		if(p2->p[i2] == nil) {
 			p3 = m->allocator(sizeof *p3);
 			if(p3 == nil)
 				return false;
 			sys_memclr((byte*)p3, sizeof *p3);
 			p2->p[i2] = p3;
 		}

 		// advance key past this leaf node
 		k = ((k >> MHeapMap_Level3Bits) + 1) << MHeapMap_Level3Bits;
 	}
 	return true;
 }

 // Initialize a new span with the given start and npages.
 void
 MSpan_Init(MSpan *span, PageID start, uintptr npages)
 {
 	span->next = nil;
 	span->prev = nil;
 	span->start = start;
 	span->npages = npages;
 	span->freelist = nil;
 	span->ref = 0;
 	span->sizeclass = 0;
 	span->state = 0;
 }

 // Initialize an empty doubly-linked list.
 void
 MSpanList_Init(MSpan *list)
 {
 	list->next = list;
 	list->prev = list;
 }

 void
 MSpanList_Remove(MSpan *span)
 {
 	if(span->prev == nil && span->next == nil)
 		return;
 	span->prev->next = span->next;
 	span->next->prev = span->prev;
 	span->prev = nil;
 	span->next = nil;
 }

 bool
 MSpanList_IsEmpty(MSpan *list)
 {
 	return list->next == list;
 }

 void
 MSpanList_Insert(MSpan *list, MSpan *span)
 {
 	if(span->next != nil || span->prev != nil)
 		throw("MSpanList_Insert");
 	span->next = list->next;
 	span->prev = list;
 	span->next->prev = span;
 	span->prev->next = span;
 }
	// 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.

	// Page heap.
	//
	// See malloc.h for overview.
	//
	// When a MSpan is in the heap free list, state == MSpanFree
	// and heapmap(s->start) == span, heapmap(s->start+s->npages-1) == span.
	//
	// When a MSpan is allocated, state == MSpanInUse
	// and heapmap(i) == span for all s->start <= i < s->start+s->npages.

	#include "runtime.h"
	#include "malloc.h"

	static MSpan MHeap_AllocLocked(MHeap, uintptr, int32);
	static bool MHeap_Grow(MHeap*, uintptr);
	static void MHeap_FreeLocked(MHeap, MSpan);
	static MSpan MHeap_AllocLarge(MHeap, uintptr);
	static MSpan BestFit(MSpan, uintptr, MSpan*);

	// Initialize the heap; fetch memory using alloc.
	void
	MHeap_Init(MHeap h, void (*alloc)(uintptr))
	{
	uint32 i;

	FixAlloc_Init(&h->spanalloc, sizeof(MSpan), alloc);
	FixAlloc_Init(&h->cachealloc, sizeof(MCache), alloc);
	MHeapMap_Init(&h->map, alloc);
	// h->mapcache needs no init
	for(i=0; i<nelem(h->free); i++)
	MSpanList_Init(&h->free[i]);
	MSpanList_Init(&h->large);
	for(i=0; i<nelem(h->central); i++)
	MCentral_Init(&h->central[i], i);
	}

	// Allocate a new span of npage pages from the heap
	// and record its size class in the HeapMap and HeapMapCache.
	MSpan*
	MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass)
	{
	MSpan *s;

	lock(h);
	s = MHeap_AllocLocked(h, npage, sizeclass);
	unlock(h);
	return s;
	}

	static MSpan*
	MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
	{
	uintptr n;
	MSpan s, t;

	// Try in fixed-size lists up to max.
	for(n=npage; n < nelem(h->free); n++) {
	if(!MSpanList_IsEmpty(&h->free[n])) {
	s = h->free[n].next;
	goto HaveSpan;
	}
	}

	// Best fit in list of large spans.
	if((s = MHeap_AllocLarge(h, npage)) == nil) {
	if(!MHeap_Grow(h, npage))
	return nil;
	if((s = MHeap_AllocLarge(h, npage)) == nil)
	return nil;
	}

	HaveSpan:
	// Mark span in use.
	if(s->state != MSpanFree)
	throw("MHeap_AllocLocked - MSpan not free");
	if(s->npages < npage)
	throw("MHeap_AllocLocked - bad npages");
	MSpanList_Remove(s);
	s->state = MSpanInUse;

	if(s->npages > npage) {
	// Trim extra and put it back in the heap.
	t = FixAlloc_Alloc(&h->spanalloc);
	MSpan_Init(t, s->start + npage, s->npages - npage);
	s->npages = npage;
	MHeapMap_Set(&h->map, t->start - 1, s);
	MHeapMap_Set(&h->map, t->start, t);
	MHeapMap_Set(&h->map, t->start + t->npages - 1, t);
	t->state = MSpanInUse;
	MHeap_FreeLocked(h, t);
	}

	// If span is being used for small objects, cache size class.
	// No matter what, cache span info, because gc needs to be
	// able to map interior pointer to containing span.
	s->sizeclass = sizeclass;
	for(n=0; n<npage; n++)
	MHeapMap_Set(&h->map, s->start+n, s);
	if(sizeclass == 0) {
	uintptr tmp;

	// If there are entries for this span, invalidate them,
	// but don't blow out cache entries about other spans.
	for(n=0; n<npage; n++)
	if(MHeapMapCache_GET(&h->mapcache, s->start+n, tmp) != 0)
	MHeapMapCache_SET(&h->mapcache, s->start+n, 0);
	} else {
	// Save cache entries for this span.
	// If there's a size class, there aren't that many pages.
	for(n=0; n<npage; n++)
	MHeapMapCache_SET(&h->mapcache, s->start+n, sizeclass);
	}

	return s;
	}

	// Allocate a span of exactly npage pages from the list of large spans.
	static MSpan*
	MHeap_AllocLarge(MHeap *h, uintptr npage)
	{
	return BestFit(&h->large, npage, nil);
	}

	// Search list for smallest span with >= npage pages.
	// If there are multiple smallest spans, take the one
	// with the earliest starting address.
	static MSpan*
	BestFit(MSpan list, uintptr npage, MSpan best)
	{
	MSpan *s;

	for(s=list->next; s != list; s=s->next) {
	if(s->npages < npage)
	continue;
	if(best == nil
	\|\| s->npages < best->npages
	\|\| (s->npages == best->npages && s->start < best->start))
	best = s;
	}
	return best;
	}

	// Try to add at least npage pages of memory to the heap,
	// returning whether it worked.
	static bool
	MHeap_Grow(MHeap *h, uintptr npage)
	{
	uintptr ask;
	void *v;
	MSpan *s;

	// Ask for a big chunk, to reduce the number of mappings
	// the operating system needs to track; also amortizes
	// the overhead of an operating system mapping.
	ask = npage<<PageShift;
	if(ask < HeapAllocChunk)
	ask = HeapAllocChunk;

	v = SysAlloc(ask);
	if(v == nil) {
	if(ask > (npage<<PageShift)) {
	ask = npage<<PageShift;
	v = SysAlloc(ask);
	}
	if(v == nil)
	return false;
	}

	// NOTE(rsc): In tcmalloc, if we've accumulated enough
	// system allocations, the heap map gets entirely allocated
	// in 32-bit mode. (In 64-bit mode that's not practical.)

	if(!MHeapMap_Preallocate(&h->map, ((uintptr)v>>PageShift) - 1, (ask>>PageShift) + 2)) {
	SysFree(v, ask);
	return false;
	}

	// Create a fake "in use" span and free it, so that the
	// right coalescing happens.
	s = FixAlloc_Alloc(&h->spanalloc);
	MSpan_Init(s, (uintptr)v>>PageShift, ask>>PageShift);
	MHeapMap_Set(&h->map, s->start, s);
	MHeapMap_Set(&h->map, s->start + s->npages - 1, s);
	s->state = MSpanInUse;
	MHeap_FreeLocked(h, s);
	return true;
	}

	// Look up the span at the given page number.
	MSpan*
	MHeap_Lookup(MHeap *h, PageID p)
	{
	return MHeapMap_Get(&h->map, p);
	}

	// Free the span back into the heap.
	void
	MHeap_Free(MHeap h, MSpan s)
	{
	lock(h);
	MHeap_FreeLocked(h, s);
	unlock(h);
	}

	static void
	MHeap_FreeLocked(MHeap h, MSpan s)
	{
	MSpan *t;

	if(s->state != MSpanInUse \|\| s->ref != 0) {
	printf("MHeap_FreeLocked - span %p ptr %p state %d ref %d\n", s, s->start<<PageShift, s->state, s->ref);
	throw("MHeap_FreeLocked - invalid free");
	}
	s->state = MSpanFree;
	MSpanList_Remove(s);

	// Coalesce with earlier, later spans.
	if((t = MHeapMap_Get(&h->map, s->start - 1)) != nil && t->state != MSpanInUse) {
	s->start = t->start;
	s->npages += t->npages;
	MHeapMap_Set(&h->map, s->start, s);
	MSpanList_Remove(t);
	FixAlloc_Free(&h->spanalloc, t);
	}
	if((t = MHeapMap_Get(&h->map, s->start + s->npages)) != nil && t->state != MSpanInUse) {
	s->npages += t->npages;
	MHeapMap_Set(&h->map, s->start + s->npages - 1, s);
	MSpanList_Remove(t);
	FixAlloc_Free(&h->spanalloc, t);
	}

	// Insert s into appropriate list.
	if(s->npages < nelem(h->free))
	MSpanList_Insert(&h->free[s->npages], s);
	else
	MSpanList_Insert(&h->large, s);

	// TODO(rsc): IncrementalScavenge() to return memory to OS.
	}

	// 3-level radix tree mapping page ids to Span*.
	void
	MHeapMap_Init(MHeapMap m, void (*allocator)(size_t))
	{
	m->allocator = allocator;
	}

	MSpan*
	MHeapMap_Get(MHeapMap *m, PageID k)
	{
	int32 i1, i2, i3;

	i3 = k & MHeapMap_Level3Mask;
	k >>= MHeapMap_Level3Bits;
	i2 = k & MHeapMap_Level2Mask;
	k >>= MHeapMap_Level2Bits;
	i1 = k & MHeapMap_Level1Mask;
	k >>= MHeapMap_Level1Bits;
	if(k != 0)
	throw("MHeapMap_Get");

	return m->p[i1]->p[i2]->s[i3];
	}

	void
	MHeapMap_Set(MHeapMap m, PageID k, MSpan s)
	{
	int32 i1, i2, i3;

	i3 = k & MHeapMap_Level3Mask;
	k >>= MHeapMap_Level3Bits;
	i2 = k & MHeapMap_Level2Mask;
	k >>= MHeapMap_Level2Bits;
	i1 = k & MHeapMap_Level1Mask;
	k >>= MHeapMap_Level1Bits;
	if(k != 0)
	throw("MHeapMap_Set");

	m->p[i1]->p[i2]->s[i3] = s;
	}

	// Allocate the storage required for entries [k, k+1, ..., k+len-1]
	// so that Get and Set calls need not check for nil pointers.
	bool
	MHeapMap_Preallocate(MHeapMap *m, PageID k, uintptr len)
	{
	uintptr end;
	int32 i1, i2;
	MHeapMapNode2 *p2;
	MHeapMapNode3 *p3;

	end = k+len;
	while(k < end) {
	if((k >> MHeapMap_TotalBits) != 0)
	return false;
	i2 = (k >> MHeapMap_Level3Bits) & MHeapMap_Level2Mask;
	i1 = (k >> (MHeapMap_Level3Bits + MHeapMap_Level2Bits)) & MHeapMap_Level1Mask;

	// first-level pointer
	if((p2 = m->p[i1]) == nil) {
	p2 = m->allocator(sizeof *p2);
	if(p2 == nil)
	return false;
	sys_memclr((byte)p2, sizeof p2);
	m->p[i1] = p2;
	}

	// second-level pointer
	if(p2->p[i2] == nil) {
	p3 = m->allocator(sizeof *p3);
	if(p3 == nil)
	return false;
	sys_memclr((byte)p3, sizeof p3);
	p2->p[i2] = p3;
	}

	// advance key past this leaf node
	k = ((k >> MHeapMap_Level3Bits) + 1) << MHeapMap_Level3Bits;
	}
	return true;
	}

	// Initialize a new span with the given start and npages.
	void
	MSpan_Init(MSpan *span, PageID start, uintptr npages)
	{
	span->next = nil;
	span->prev = nil;
	span->start = start;
	span->npages = npages;
	span->freelist = nil;
	span->ref = 0;
	span->sizeclass = 0;
	span->state = 0;
	}

	// Initialize an empty doubly-linked list.
	void
	MSpanList_Init(MSpan *list)
	{
	list->next = list;
	list->prev = list;
	}

	void
	MSpanList_Remove(MSpan *span)
	{
	if(span->prev == nil && span->next == nil)
	return;
	span->prev->next = span->next;
	span->next->prev = span->prev;
	span->prev = nil;
	span->next = nil;
	}

	bool
	MSpanList_IsEmpty(MSpan *list)
	{
	return list->next == list;
	}

	void
	MSpanList_Insert(MSpan list, MSpan span)
	{
	if(span->next != nil \|\| span->prev != nil)
	throw("MSpanList_Insert");
	span->next = list->next;
	span->prev = list;
	span->next->prev = span;
	span->prev->next = span;
	}