// Free n objects from a span s back into the central free list c.
// Called from GC.
void
runtime·MCentral_FreeSpan(MCentral *c, MSpan *s, int32 n, MLink *start, MLink *end)
{
int32 size;
runtime·lock(c);
// Move to nonempty if necessary.
if(s->freelist == nil) {
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->nonempty, s);
}
// Add the objects back to s's free list.
end->next = s->freelist;
s->freelist = start;
s->ref -= n;
c->nfree += n;
// If s is completely freed, return it to the heap.
if(s->ref == 0) {
size = runtime·class_to_size[c->sizeclass];
runtime·MSpanList_Remove(s);
*(uintptr*)(s->start<<PageShift) = 1; // needs zeroing
s->freelist = nil;
c->nfree -= (s->npages << PageShift) / size;
runtime·unlock(c);
runtime·unmarkspan((byte*)(s->start<<PageShift), s->npages<<PageShift);
runtime·MHeap_Free(runtime·mheap, s, 0);
} else {
runtime·unlock(c);
}
}
// Free n objects from a span s back into the central free list c.
// Called during sweep.
// Returns true if the span was returned to heap. Sets sweepgen to
// the latest generation.
bool
runtime·MCentral_FreeSpan(MCentral *c, MSpan *s, int32 n, MLink *start, MLink *end)
{
if(s->incache)
runtime·throw("freespan into cached span");
runtime·lock(c);
// Move to nonempty if necessary.
if(s->freelist == nil) {
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->nonempty, s);
}
// Add the objects back to s's free list.
end->next = s->freelist;
s->freelist = start;
s->ref -= n;
c->nfree += n;
// delay updating sweepgen until here. This is the signal that
// the span may be used in an MCache, so it must come after the
// linked list operations above (actually, just after the
// lock of c above.)
runtime·atomicstore(&s->sweepgen, runtime·mheap.sweepgen);
if(s->ref != 0) {
runtime·unlock(c);
return false;
}
// s is completely freed, return it to the heap.
MCentral_ReturnToHeap(c, s); // unlocks c
return true;
}
// Return span from an MCache.
void
runtime·MCentral_UncacheSpan(MCentral *c, MSpan *s)
{
MLink *v;
int32 cap, n;
runtime·lock(c);
s->incache = false;
// Move any explicitly freed items from the freebuf to the freelist.
while((v = s->freebuf) != nil) {
s->freebuf = v->next;
runtime·markfreed(v);
v->next = s->freelist;
s->freelist = v;
s->ref--;
}
if(s->ref == 0) {
// Free back to heap. Unlikely, but possible.
MCentral_ReturnToHeap(c, s); // unlocks c
return;
}
cap = (s->npages << PageShift) / s->elemsize;
n = cap - s->ref;
if(n > 0) {
c->nfree += n;
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->nonempty, s);
}
runtime·unlock(c);
}
// Sweeps spans in list until reclaims at least npages into heap.
// Returns the actual number of pages reclaimed.
static uintptr
MHeap_ReclaimList(MHeap *h, MSpan *list, uintptr npages)
{
MSpan *s;
uintptr n;
uint32 sg;
n = 0;
sg = runtime·mheap.sweepgen;
retry:
for(s = list->next; s != list; s = s->next) {
if(s->sweepgen == sg-2 && runtime·cas(&s->sweepgen, sg-2, sg-1)) {
runtime·MSpanList_Remove(s);
// swept spans are at the end of the list
runtime·MSpanList_InsertBack(list, s);
runtime·unlock(&h->lock);
n += runtime·MSpan_Sweep(s);
runtime·lock(&h->lock);
if(n >= npages)
return n;
// the span could have been moved elsewhere
goto retry;
}
if(s->sweepgen == sg-1) {
// the span is being sweept by background sweeper, skip
continue;
}
// already swept empty span,
// all subsequent ones must also be either swept or in process of sweeping
break;
}
return n;
}
// Allocates a span of the given size. h must be locked.
// The returned span has been removed from the
// free list, but its state is still MSpanFree.
static MSpan*
MHeap_AllocSpanLocked(MHeap *h, uintptr npage)
{
uintptr n;
MSpan *s, *t;
PageID p;
// Try in fixed-size lists up to max.
for(n=npage; n < nelem(h->free); n++) {
if(!runtime·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)
runtime·throw("MHeap_AllocLocked - MSpan not free");
if(s->npages < npage)
runtime·throw("MHeap_AllocLocked - bad npages");
runtime·MSpanList_Remove(s);
if(s->next != nil || s->prev != nil)
runtime·throw("still in list");
if(s->npreleased > 0) {
runtime·SysUsed((void*)(s->start<<PageShift), s->npages<<PageShift);
mstats.heap_released -= s->npreleased<<PageShift;
s->npreleased = 0;
}
if(s->npages > npage) {
// Trim extra and put it back in the heap.
t = runtime·FixAlloc_Alloc(&h->spanalloc);
runtime·MSpan_Init(t, s->start + npage, s->npages - npage);
s->npages = npage;
p = t->start;
p -= ((uintptr)h->arena_start>>PageShift);
if(p > 0)
h->spans[p-1] = s;
h->spans[p] = t;
h->spans[p+t->npages-1] = t;
t->needzero = s->needzero;
s->state = MSpanStack; // prevent coalescing with s
t->state = MSpanStack;
MHeap_FreeSpanLocked(h, t);
t->unusedsince = s->unusedsince; // preserve age (TODO: wrong: t is possibly merged and/or deallocated at this point)
s->state = MSpanFree;
}
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);
mstats.mspan_inuse = h->spanalloc.inuse;
mstats.mspan_sys = h->spanalloc.sys;
}
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);
mstats.mspan_inuse = h->spanalloc.inuse;
mstats.mspan_sys = h->spanalloc.sys;
}
// 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.
}
static MSpan*
MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
{
uintptr n;
MSpan *s, *t;
PageID p;
// Try in fixed-size lists up to max.
for(n=npage; n < nelem(h->free); n++) {
if(!runtime·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)
runtime·throw("MHeap_AllocLocked - MSpan not free");
if(s->npages < npage)
runtime·throw("MHeap_AllocLocked - bad npages");
runtime·MSpanList_Remove(s);
s->state = MSpanInUse;
mstats.heap_idle -= s->npages<<PageShift;
mstats.heap_released -= s->npreleased<<PageShift;
s->npreleased = 0;
if(s->npages > npage) {
// Trim extra and put it back in the heap.
t = runtime·FixAlloc_Alloc(&h->spanalloc);
mstats.mspan_inuse = h->spanalloc.inuse;
mstats.mspan_sys = h->spanalloc.sys;
runtime·MSpan_Init(t, s->start + npage, s->npages - npage);
s->npages = npage;
p = t->start;
if(sizeof(void*) == 8)
p -= ((uintptr)h->arena_start>>PageShift);
if(p > 0)
h->map[p-1] = s;
h->map[p] = t;
h->map[p+t->npages-1] = t;
*(uintptr*)(t->start<<PageShift) = *(uintptr*)(s->start<<PageShift); // copy "needs zeroing" mark
t->state = MSpanInUse;
MHeap_FreeLocked(h, t);
}
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);
mstats.mspan_inuse = h->spanalloc.inuse;
mstats.mspan_sys = h->spanalloc.sys;
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);
}
// Record 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);
return s;
}
// Helper: free one object back into the central free list.
static void
MCentral_Free(MCentral *c, void *v)
{
MSpan *s;
MLink *p;
int32 size;
// Find span for v.
s = runtime·MHeap_Lookup(runtime·mheap, v);
if(s == nil || s->ref == 0)
runtime·throw("invalid free");
// Move to nonempty if necessary.
if(s->freelist == nil) {
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->nonempty, s);
}
// Add v back to s's free list.
p = v;
p->next = s->freelist;
s->freelist = p;
c->nfree++;
// If s is completely freed, return it to the heap.
if(--s->ref == 0) {
size = runtime·class_to_size[c->sizeclass];
runtime·MSpanList_Remove(s);
runtime·unmarkspan((byte*)(s->start<<PageShift), s->npages<<PageShift);
*(uintptr*)(s->start<<PageShift) = 1; // needs zeroing
s->freelist = nil;
c->nfree -= (s->npages << PageShift) / size;
runtime·unlock(c);
runtime·MHeap_Free(runtime·mheap, s, 0);
runtime·lock(c);
}
}
// Return s to the heap. s must be unused (s->ref == 0). Unlocks c.
static void
MCentral_ReturnToHeap(MCentral *c, MSpan *s)
{
int32 size;
size = runtime·class_to_size[c->sizeclass];
runtime·MSpanList_Remove(s);
s->needzero = 1;
s->freelist = nil;
if(s->ref != 0)
runtime·throw("ref wrong");
c->nfree -= (s->npages << PageShift) / size;
runtime·unlock(c);
runtime·unmarkspan((byte*)(s->start<<PageShift), s->npages<<PageShift);
runtime·MHeap_Free(&runtime·mheap, s, 0);
}
// Allocate up to n objects from the central free list.
// Return the number of objects allocated.
// The objects are linked together by their first words.
// On return, *pstart points at the first object.
int32
runtime·MCentral_AllocList(MCentral *c, int32 n, MLink **pfirst)
{
MSpan *s;
MLink *first, *last;
int32 cap, avail, i;
runtime·lock(c);
// Replenish central list if empty.
if(runtime·MSpanList_IsEmpty(&c->nonempty)) {
if(!MCentral_Grow(c)) {
runtime·unlock(c);
*pfirst = nil;
return 0;
}
}
s = c->nonempty.next;
cap = (s->npages << PageShift) / s->elemsize;
avail = cap - s->ref;
if(avail < n)
n = avail;
// First one is guaranteed to work, because we just grew the list.
first = s->freelist;
last = first;
for(i=1; i<n; i++) {
last = last->next;
}
s->freelist = last->next;
last->next = nil;
s->ref += n;
c->nfree -= n;
if(n == avail) {
if(s->freelist != nil || s->ref != cap) {
runtime·throw("invalid freelist");
}
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->empty, s);
}
runtime·unlock(c);
*pfirst = first;
return n;
}
// Helper: allocate one object from the central free list.
static void*
MCentral_Alloc(MCentral *c)
{
MSpan *s;
MLink *v;
if(runtime·MSpanList_IsEmpty(&c->nonempty))
return nil;
s = c->nonempty.next;
s->ref++;
v = s->freelist;
s->freelist = v->next;
if(s->freelist == nil) {
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->empty, s);
}
return v;
}
// Return span from an MCache.
void
runtime·MCentral_UncacheSpan(MCentral *c, MSpan *s)
{
int32 cap, n;
runtime·lock(&c->lock);
s->incache = false;
if(s->ref == 0)
runtime·throw("uncaching full span");
cap = (s->npages << PageShift) / s->elemsize;
n = cap - s->ref;
if(n > 0) {
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->nonempty, s);
}
runtime·unlock(&c->lock);
}
// Helper: free one object back into the central free list.
// Caller must hold lock on c on entry. Holds lock on exit.
static void
MCentral_Free(MCentral *c, MLink *v)
{
MSpan *s;
// Find span for v.
s = runtime·MHeap_Lookup(&runtime·mheap, v);
if(s == nil || s->ref == 0)
runtime·throw("invalid free");
if(s->sweepgen != runtime·mheap.sweepgen)
runtime·throw("free into unswept span");
// If the span is currently being used unsynchronized by an MCache,
// we can't modify the freelist. Add to the freebuf instead. The
// items will get moved to the freelist when the span is returned
// by the MCache.
if(s->incache) {
v->next = s->freebuf;
s->freebuf = v;
return;
}
// Move span to nonempty if necessary.
if(s->freelist == nil) {
runtime·MSpanList_Remove(s);
runtime·MSpanList_Insert(&c->nonempty, s);
}
// Add the object to span's free list.
runtime·markfreed(v);
v->next = s->freelist;
s->freelist = v;
s->ref--;
c->nfree++;
// If s is completely freed, return it to the heap.
if(s->ref == 0) {
MCentral_ReturnToHeap(c, s); // unlocks c
runtime·lock(c);
}
}
runtime·MCentral_CacheSpan(MCentral *c)
{
MSpan *s;
int32 cap, n;
uint32 sg;
runtime·lock(&c->lock);
sg = runtime·mheap.sweepgen;
retry:
for(s = c->nonempty.next; s != &c->nonempty; s = s->next) {
if(s->sweepgen == sg-2 && runtime·cas(&s->sweepgen, sg-2, sg-1)) {
runtime·unlock(&c->lock);
runtime·MSpan_Sweep(s);
runtime·lock(&c->lock);
// the span could have been moved to heap, retry
goto retry;
}
if(s->sweepgen == sg-1) {
// the span is being swept by background sweeper, skip
continue;
}
// we have a nonempty span that does not require sweeping, allocate from it
goto havespan;
}
for(s = c->empty.next; s != &c->empty; s = s->next) {
if(s->sweepgen == sg-2 && runtime·cas(&s->sweepgen, sg-2, sg-1)) {
// we have an empty span that requires sweeping,
// sweep it and see if we can free some space in it
runtime·MSpanList_Remove(s);
// swept spans are at the end of the list
runtime·MSpanList_InsertBack(&c->empty, s);
runtime·unlock(&c->lock);
runtime·MSpan_Sweep(s);
runtime·lock(&c->lock);
// the span could be moved to nonempty or heap, retry
goto retry;
}
if(s->sweepgen == sg-1) {
// the span is being swept by background sweeper, skip
continue;
}
// already swept empty span,
// all subsequent ones must also be either swept or in process of sweeping
break;
}
// Replenish central list if empty.
if(!MCentral_Grow(c)) {
runtime·unlock(&c->lock);
return nil;
}
goto retry;
havespan:
cap = (s->npages << PageShift) / s->elemsize;
n = cap - s->ref;
if(n == 0)
runtime·throw("empty span");
if(s->freelist == nil)
runtime·throw("freelist empty");
runtime·MSpanList_Remove(s);
runtime·MSpanList_InsertBack(&c->empty, s);
s->incache = true;
runtime·unlock(&c->lock);
return s;
}
static MSpan*
MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
{
uintptr n;
MSpan *s, *t;
PageID p;
// Try in fixed-size lists up to max.
for(n=npage; n < nelem(h->free); n++) {
if(!runtime·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)
runtime·throw("MHeap_AllocLocked - MSpan not free");
if(s->npages < npage)
runtime·throw("MHeap_AllocLocked - bad npages");
runtime·MSpanList_Remove(s);
s->state = MSpanInUse;
mstats.heap_idle -= s->npages<<PageShift;
mstats.heap_released -= s->npreleased<<PageShift;
if(s->npreleased > 0) {
// We have called runtime·SysUnused with these pages, and on
// Unix systems it called madvise. At this point at least
// some BSD-based kernels will return these pages either as
// zeros or with the old data. For our caller, the first word
// in the page indicates whether the span contains zeros or
// not (this word was set when the span was freed by
// MCentral_Free or runtime·MCentral_FreeSpan). If the first
// page in the span is returned as zeros, and some subsequent
// page is returned with the old data, then we will be
// returning a span that is assumed to be all zeros, but the
// actual data will not be all zeros. Avoid that problem by
// explicitly marking the span as not being zeroed, just in
// case. The beadbead constant we use here means nothing, it
// is just a unique constant not seen elsewhere in the
// runtime, as a clue in case it turns up unexpectedly in
// memory or in a stack trace.
*(uintptr*)(s->start<<PageShift) = (uintptr)0xbeadbeadbeadbeadULL;
}
s->npreleased = 0;
if(s->npages > npage) {
// Trim extra and put it back in the heap.
t = runtime·FixAlloc_Alloc(&h->spanalloc);
mstats.mspan_inuse = h->spanalloc.inuse;
mstats.mspan_sys = h->spanalloc.sys;
runtime·MSpan_Init(t, s->start + npage, s->npages - npage);
s->npages = npage;
p = t->start;
if(sizeof(void*) == 8)
p -= ((uintptr)h->arena_start>>PageShift);
if(p > 0)
h->map[p-1] = s;
h->map[p] = t;
h->map[p+t->npages-1] = t;
*(uintptr*)(t->start<<PageShift) = *(uintptr*)(s->start<<PageShift); // copy "needs zeroing" mark
t->state = MSpanInUse;
MHeap_FreeLocked(h, t);
t->unusedsince = s->unusedsince; // preserve age
}
