*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.14 1999/02/13 23:20:09 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.15 1999/05/22 23:19:37 tgl Exp $
*
* NOTE:
* This is a new (Feb. 05, 1999) implementation of the allocation set
* many small allocations in a few bigger blocks. AllocSetFree() does
* never free() memory really. It just add's the free'd area to some
* list for later reuse by AllocSetAlloc(). All memory blocks are free()'d
- * on AllocSetReset() at once, what happens when the memory context gets
+ * at once on AllocSetReset(), which happens when the memory context gets
* destroyed.
* Jan Wieck
*-------------------------------------------------------------------------
#undef realloc
-#define ALLOC_BLOCK_SIZE 8192
-#define ALLOC_CHUNK_LIMIT 512
+/*--------------------
+ * Chunk freelist k holds chunks of size 1 << (k + ALLOC_MINBITS),
+ * for k = 0 .. ALLOCSET_NUM_FREELISTS-2.
+ * The last freelist holds all larger chunks.
+ *
+ * CAUTION: ALLOC_MINBITS must be large enough so that
+ * 1<<ALLOC_MINBITS is at least MAXALIGN,
+ * or we may fail to align the smallest chunks adequately.
+ * 16-byte alignment is enough on all currently known machines.
+ *--------------------
+ */
+
+#define ALLOC_MINBITS 4 /* smallest chunk size is 16 bytes */
+#define ALLOC_SMALLCHUNK_LIMIT (1 << (ALLOCSET_NUM_FREELISTS-2+ALLOC_MINBITS))
+/* Size of largest chunk that we use a fixed size for */
+
+/*--------------------
+ * The first block allocated for an allocset has size ALLOC_MIN_BLOCK_SIZE.
+ * Each time we have to allocate another block, we double the block size
+ * (if possible, and without exceeding ALLOC_MAX_BLOCK_SIZE), so as to reduce
+ * the load on "malloc".
+ *
+ * Blocks allocated to hold oversize chunks do not follow this rule, however;
+ * they are just however big they need to be.
+ *--------------------
+ */
+
+#define ALLOC_MIN_BLOCK_SIZE 8192
+#define ALLOC_MAX_BLOCK_SIZE (8 * 1024 * 1024)
+
#define ALLOC_BLOCKHDRSZ MAXALIGN(sizeof(AllocBlockData))
#define ALLOC_CHUNKHDRSZ MAXALIGN(sizeof(AllocChunkData))
{
int idx = 0;
- size = (size - 1) >> 4;
- while (size != 0 && idx < 7)
+ if (size > 0)
{
- idx++;
- size >>= 1;
+ size = (size - 1) >> ALLOC_MINBITS;
+ while (size != 0 && idx < ALLOCSET_NUM_FREELISTS-1)
+ {
+ idx++;
+ size >>= 1;
+ }
}
return idx;
AllocChunk freeref = NULL;
int fidx;
Size chunk_size;
+ Size blksize;
AssertArg(AllocSetIsValid(set));
}
/*
- * If found, remove it from the free list, make it again
+ * If one is found, remove it from the free list, make it again
* a member of the alloc set and return it's data address.
*
*/
}
/*
- * If requested size exceeds smallchunk limit, allocate a separate,
- * entire used block for this allocation
- *
+ * Choose the actual chunk size to allocate.
*/
- if (size > ALLOC_CHUNK_LIMIT)
+ if (size > ALLOC_SMALLCHUNK_LIMIT)
+ chunk_size = MAXALIGN(size);
+ else
+ chunk_size = 1 << (fidx + ALLOC_MINBITS);
+ Assert(chunk_size >= size);
+
+ /*
+ * If there is enough room in the active allocation block,
+ * always allocate the chunk there.
+ */
+
+ if ((block = set->blocks) != NULL)
{
- Size blksize;
+ Size have_free = block->endptr - block->freeptr;
- chunk_size = MAXALIGN(size);
+ if (have_free < (chunk_size + ALLOC_CHUNKHDRSZ))
+ block = NULL;
+ }
+
+ /*
+ * Otherwise, if requested size exceeds smallchunk limit,
+ * allocate an entire separate block for this allocation
+ *
+ */
+ if (block == NULL && size > ALLOC_SMALLCHUNK_LIMIT)
+ {
blksize = chunk_size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
block = (AllocBlock) malloc(blksize);
if (block == NULL)
elog(FATAL, "Memory exhausted in AllocSetAlloc()");
block->aset = set;
- block->freeptr = block->endptr = ((char *)block) + ALLOC_BLOCKHDRSZ;
+ block->freeptr = block->endptr = ((char *)block) + blksize;
chunk = (AllocChunk) (((char *)block) + ALLOC_BLOCKHDRSZ);
chunk->aset = set;
chunk->size = chunk_size;
+ /*
+ * Try to stick the block underneath the active allocation block,
+ * so that we don't lose the use of the space remaining therein.
+ */
if (set->blocks != NULL)
{
block->next = set->blocks->next;
return AllocChunkGetPointer(chunk);
}
- chunk_size = 16 << fidx;
-
- if ((block = set->blocks) != NULL)
- {
- Size have_free = block->endptr - block->freeptr;
-
- if (have_free < (chunk_size + ALLOC_CHUNKHDRSZ))
- block = NULL;
- }
-
+ /*
+ * Time to create a new regular block?
+ */
if (block == NULL)
{
- block = (AllocBlock) malloc(ALLOC_BLOCK_SIZE);
+ if (set->blocks == NULL)
+ {
+ blksize = ALLOC_MIN_BLOCK_SIZE;
+ block = (AllocBlock) malloc(blksize);
+ }
+ else
+ {
+ /* Get size of prior block */
+ blksize = set->blocks->endptr - ((char *) set->blocks);
+ /* Special case: if very first allocation was for a large chunk,
+ * could have a funny-sized top block. Do something reasonable.
+ */
+ if (blksize < ALLOC_MIN_BLOCK_SIZE)
+ blksize = ALLOC_MIN_BLOCK_SIZE;
+ /* Crank it up, but not past max */
+ blksize <<= 1;
+ if (blksize > ALLOC_MAX_BLOCK_SIZE)
+ blksize = ALLOC_MAX_BLOCK_SIZE;
+ /* Try to allocate it */
+ block = (AllocBlock) malloc(blksize);
+ /*
+ * We could be asking for pretty big blocks here, so cope if
+ * malloc fails. But give up if there's less than a meg or so
+ * available...
+ */
+ while (block == NULL && blksize > 1024*1024)
+ {
+ blksize >>= 1;
+ block = (AllocBlock) malloc(blksize);
+ }
+ }
+
if (block == NULL)
elog(FATAL, "Memory exhausted in AllocSetAlloc()");
block->aset = set;
- block->next = set->blocks;
block->freeptr = ((char *)block) + ALLOC_BLOCKHDRSZ;
- block->endptr = ((char *)block) + ALLOC_BLOCK_SIZE;
+ block->endptr = ((char *)block) + blksize;
+ block->next = set->blocks;
set->blocks = block;
}
+ /*
+ * OK, do the allocation
+ */
chunk = (AllocChunk)(block->freeptr);
chunk->aset = (void *)set;
chunk->size = chunk_size;
block->freeptr += (chunk_size + ALLOC_CHUNKHDRSZ);
+ Assert(block->freeptr <= block->endptr);
return AllocChunkGetPointer(chunk);
}
* Maybe the allocated area already is >= the new size.
*
*/
- if (AllocPointerGetSize(pointer) >= size)
+ oldsize = AllocPointerGetSize(pointer);
+ if (oldsize >= size)
return pointer;
/* allocate new pointer */
newPointer = AllocSetAlloc(set, size);
/* fill new memory */
- oldsize = AllocPointerGetSize(pointer);
memmove(newPointer, pointer, (oldsize < size) ? oldsize : size);
/* free old pointer */
*
* Copyright (c) 1994, Regents of the University of California
*
- * $Id: memutils.h,v 1.23 1999/03/25 19:05:19 tgl Exp $
+ * $Id: memutils.h,v 1.24 1999/05/22 23:19:36 tgl Exp $
*
* NOTES
* some of the information in this file will be moved to
* an allocation is requested for a set, memory is allocated and a
* pointer is returned. Subsequently, this memory may be freed or
* reallocated. In addition, an allocation set may be reset which
- * will cause all allocated memory to be freed.
+ * will cause all memory allocated within it to be freed.
*
* Allocations may occur in four different modes. The mode of
* allocation does not affect the behavior of allocations except in
* and freed very frequently. This is a good choice when allocation
* characteristics are unknown. This is the default mode.
*
- * "Static" mode attemts to allocate space as efficiently as possible
+ * "Static" mode attempts to allocate space as efficiently as possible
* without regard to freeing memory. This mode should be chosen only
* when it is known that many allocations will occur but that very
* little of the allocated memory will be explicitly freed.
* Allocation sets are not automatically reset on a system reset.
* Higher level code is responsible for cleaning up.
*
- * There may other modes in the future.
+ * There may be other modes in the future.
*/
/*
* The prefix of each piece of memory in an AllocBlock
*/
typedef struct AllocChunkData {
+ /* aset is the owning aset if allocated, or the freelist link if free */
void *aset;
+ /* size is always the chunk size */
Size size;
} AllocChunkData;
typedef struct AllocSetData
{
struct AllocBlockData *blocks;
- struct AllocChunkData *freelist[8];
+#define ALLOCSET_NUM_FREELISTS 8
+ struct AllocChunkData *freelist[ALLOCSET_NUM_FREELISTS];
/* Note: this will change in the future to support other modes */
} AllocSetData;
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