// 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);
n += runtime_MSpan_Sweep(s);
runtime_lock(h);
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;
}
// Allocate a list of objects from the central free list.
// Return the number of objects allocated.
// The objects are linked together by their first words.
// On return, *pfirst points at the first object.
int32
runtime_MCentral_AllocList(MCentral *c, MLink **pfirst)
{
MSpan *s;
int32 cap, n;
uint32 sg;
runtime_lock(c);
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);
runtime_MSpan_Sweep(s);
runtime_lock(c);
// 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);
runtime_MSpan_Sweep(s);
runtime_lock(c);
// 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);
*pfirst = nil;
return 0;
}
s = c->nonempty.next;
havespan:
cap = (s->npages << PageShift) / s->elemsize;
n = cap - s->ref;
*pfirst = s->freelist;
s->freelist = nil;
s->ref += n;
c->nfree -= n;
runtime_MSpanList_Remove(s);
runtime_MSpanList_InsertBack(&c->empty, s);
runtime_unlock(c);
return n;
}
