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// 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*);
static void
RecordSpan(void *vh, byte *p)
{
MHeap *h;
MSpan *s;
h = vh;
s = (MSpan*)p;
s->allnext = h->allspans;
h->allspans = s;
}
// Initialize the heap; fetch memory using alloc.
void
MHeap_Init(MHeap *h, void *(*alloc)(uintptr))
{
uint32 i;
FixAlloc_Init(&h->spanalloc, sizeof(MSpan), alloc, RecordSpan, h);
FixAlloc_Init(&h->cachealloc, sizeof(MCache), alloc, nil, nil);
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);
if(s != nil)
mstats.inuse_pages += npage;
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.
// Page number is guaranteed to be in map
// and is guaranteed to be start or end of span.
MSpan*
MHeap_Lookup(MHeap *h, PageID p)
{
return MHeapMap_Get(&h->map, p);
}
// Look up the span at the given page number.
// Page number is *not* guaranteed to be in map
// and may be anywhere in the span.
// Map entries for the middle of a span are only
// valid for allocated spans. Free spans may have
// other garbage in their middles, so we have to
// check for that.
MSpan*
MHeap_LookupMaybe(MHeap *h, PageID p)
{
MSpan *s;
s = MHeapMap_GetMaybe(&h->map, p);
if(s == nil || p < s->start || p - s->start >= s->npages)
return nil;
if(s->state != MSpanInUse)
return nil;
return s;
}
// Free the span back into the heap.
void
MHeap_Free(MHeap *h, MSpan *s)
{
lock(h);
mstats.inuse_pages -= s->npages;
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);
t->state = MSpanDead;
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);
t->state = MSpanDead;
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.
}
// 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->state = MSpanListHead;
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;
}