1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
7 // See malloc.h for an overview.
9 // The MCentral doesn't actually contain the list of free objects; the MSpan does.
10 // Each MCentral is two lists of MSpans: those with free objects (c->nonempty)
11 // and those that are completely allocated (c->empty).
13 // TODO(rsc): tcmalloc uses a "transfer cache" to split the list
14 // into sections of class_to_transfercount[sizeclass] objects
15 // so that it is faster to move those lists between MCaches and MCentrals.
20 static bool MCentral_Grow(MCentral
*c
);
21 static void* MCentral_Alloc(MCentral
*c
);
22 static void MCentral_Free(MCentral
*c
, void *v
);
24 // Initialize a single central free list.
26 runtime_MCentral_Init(MCentral
*c
, int32 sizeclass
)
29 c
->sizeclass
= sizeclass
;
30 runtime_MSpanList_Init(&c
->nonempty
);
31 runtime_MSpanList_Init(&c
->empty
);
34 // Allocate up to n objects from the central free list.
35 // Return the number of objects allocated.
36 // The objects are linked together by their first words.
37 // On return, *pstart points at the first object and *pend at the last.
39 runtime_MCentral_AllocList(MCentral
*c
, int32 n
, MLink
**pfirst
)
41 MLink
*first
, *last
, *v
;
45 // Replenish central list if empty.
46 if(runtime_MSpanList_IsEmpty(&c
->nonempty
)) {
47 if(!MCentral_Grow(c
)) {
54 // Copy from list, up to n.
55 // First one is guaranteed to work, because we just grew the list.
56 first
= MCentral_Alloc(c
);
58 for(i
=1; i
<n
&& (v
= MCentral_Alloc(c
)) != nil
; i
++) {
70 // Helper: allocate one object from the central free list.
72 MCentral_Alloc(MCentral
*c
)
77 if(runtime_MSpanList_IsEmpty(&c
->nonempty
))
82 s
->freelist
= v
->next
;
83 if(s
->freelist
== nil
) {
84 runtime_MSpanList_Remove(s
);
85 runtime_MSpanList_Insert(&c
->empty
, s
);
90 // Free n objects back into the central free list.
91 // Return the number of objects allocated.
92 // The objects are linked together by their first words.
93 // On return, *pstart points at the first object and *pend at the last.
95 runtime_MCentral_FreeList(MCentral
*c
, int32 n
, MLink
*start
)
99 // Assume next == nil marks end of list.
100 // n and end would be useful if we implemented
101 // the transfer cache optimization in the TODO above.
105 for(v
=start
; v
; v
=next
) {
112 // Helper: free one object back into the central free list.
114 MCentral_Free(MCentral
*c
, void *v
)
121 s
= runtime_MHeap_Lookup(&runtime_mheap
, v
);
122 if(s
== nil
|| s
->ref
== 0)
123 runtime_throw("invalid free");
125 // Move to nonempty if necessary.
126 if(s
->freelist
== nil
) {
127 runtime_MSpanList_Remove(s
);
128 runtime_MSpanList_Insert(&c
->nonempty
, s
);
131 // Add v back to s's free list.
133 p
->next
= s
->freelist
;
137 // If s is completely freed, return it to the heap.
139 size
= runtime_class_to_size
[c
->sizeclass
];
140 runtime_MSpanList_Remove(s
);
141 runtime_unmarkspan((byte
*)(s
->start
<<PageShift
), s
->npages
<<PageShift
);
142 *(uintptr
*)(s
->start
<<PageShift
) = 1; // needs zeroing
144 c
->nfree
-= (s
->npages
<< PageShift
) / size
;
146 runtime_MHeap_Free(&runtime_mheap
, s
, 0);
152 runtime_MGetSizeClassInfo(int32 sizeclass
, uintptr
*sizep
, int32
*npagesp
, int32
*nobj
)
157 npages
= runtime_class_to_allocnpages
[sizeclass
];
158 size
= runtime_class_to_size
[sizeclass
];
161 *nobj
= (npages
<< PageShift
) / size
;
164 // Fetch a new span from the heap and
165 // carve into objects for the free list.
167 MCentral_Grow(MCentral
*c
)
176 runtime_MGetSizeClassInfo(c
->sizeclass
, &size
, &npages
, &n
);
177 s
= runtime_MHeap_Alloc(&runtime_mheap
, npages
, c
->sizeclass
, 0);
179 // TODO(rsc): Log out of memory
184 // Carve span into sequence of blocks.
185 tailp
= &s
->freelist
;
186 p
= (byte
*)(s
->start
<< PageShift
);
187 s
->limit
= p
+ size
*n
;
195 runtime_markspan((byte
*)(s
->start
<<PageShift
), size
, n
, size
*n
< (s
->npages
<<PageShift
));
199 runtime_MSpanList_Insert(&c
->nonempty
, s
);