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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.
// Central free lists.
//
// See malloc.h for an overview.
//
// The MCentral doesn't actually contain the list of free objects; the MSpan does.
// Each MCentral is two lists of MSpans: those with free objects (c->nonempty)
// and those that are completely allocated (c->empty).
//
// TODO(rsc): tcmalloc uses a "transfer cache" to split the list
// into sections of class_to_transfercount[sizeclass] objects
// so that it is faster to move those lists between MCaches and MCentrals.
#include "runtime.h"
#include "arch_GOARCH.h"
#include "malloc.h"
static bool MCentral_Grow(MCentral *c);
static void MCentral_Free(MCentral *c, void *v);
// Initialize a single central free list.
void
runtime·MCentral_Init(MCentral *c, int32 sizeclass)
{
c->sizeclass = sizeclass;
runtime·MSpanList_Init(&c->nonempty);
runtime·MSpanList_Init(&c->empty);
}
// 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;
}
// Free n objects back into the central free list.
void
runtime·MCentral_FreeList(MCentral *c, int32 n, MLink *start)
{
MLink *v, *next;
// Assume next == nil marks end of list.
// n and end would be useful if we implemented
// the transfer cache optimization in the TODO above.
USED(n);
runtime·lock(c);
for(v=start; v; v=next) {
next = v->next;
MCentral_Free(c, v);
}
runtime·unlock(c);
}
// 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);
}
}
// 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);
}
}
void
runtime·MGetSizeClassInfo(int32 sizeclass, uintptr *sizep, int32 *npagesp, int32 *nobj)
{
int32 size;
int32 npages;
npages = runtime·class_to_allocnpages[sizeclass];
size = runtime·class_to_size[sizeclass];
*npagesp = npages;
*sizep = size;
*nobj = (npages << PageShift) / size;
}
// Fetch a new span from the heap and
// carve into objects for the free list.
static bool
MCentral_Grow(MCentral *c)
{
int32 i, n, npages;
uintptr size;
MLink **tailp, *v;
byte *p;
MSpan *s;
runtime·unlock(c);
runtime·MGetSizeClassInfo(c->sizeclass, &size, &npages, &n);
s = runtime·MHeap_Alloc(runtime·mheap, npages, c->sizeclass, 0, 1);
if(s == nil) {
// TODO(rsc): Log out of memory
runtime·lock(c);
return false;
}
// Carve span into sequence of blocks.
tailp = &s->freelist;
p = (byte*)(s->start << PageShift);
s->limit = p + size*n;
for(i=0; i<n; i++) {
v = (MLink*)p;
*tailp = v;
tailp = &v->next;
p += size;
}
*tailp = nil;
runtime·markspan((byte*)(s->start<<PageShift), size, n, size*n < (s->npages<<PageShift));
runtime·lock(c);
c->nfree += n;
runtime·MSpanList_Insert(&c->nonempty, s);
return true;
}
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