Alter AllocSet routines so that requests larger than
ALLOC_BIGCHUNK_LIMIT are always allocated as separate malloc() blocks, and are free()d immediately upon pfree(). Also, if such a chunk is enlarged with repalloc(), translate the operation into a realloc() so as to minimize memory usage. Of course, these large chunks still get freed automatically if the alloc set is reset. I have set ALLOC_BIGCHUNK_LIMIT at 64K for now, but perhaps another size would be better?
This commit is contained in:
Tom Lane
parent
1b81fd7793
commit
2b67dc5387
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@ -7,18 +7,26 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.20 1999/07/17 20:18:13 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.21 1999/08/24 20:11:17 tgl Exp $
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*
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* NOTE:
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* This is a new (Feb. 05, 1999) implementation of the allocation set
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* routines. AllocSet...() does not use OrderedSet...() any more.
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* Instead it manages allocations in a block pool by itself, combining
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* many small allocations in a few bigger blocks. AllocSetFree() does
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* never free() memory really. It just add's the free'd area to some
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* many small allocations in a few bigger blocks. AllocSetFree() normally
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* doesn't free() memory really. It just add's the free'd area to some
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* list for later reuse by AllocSetAlloc(). All memory blocks are free()'d
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* at once on AllocSetReset(), which happens when the memory context gets
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* destroyed.
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* Jan Wieck
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*
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* Performance improvement from Tom Lane, 8/99: for extremely large request
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* sizes, we do want to be able to give the memory back to free() as soon
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* as it is pfree()'d. Otherwise we risk tying up a lot of memory in
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* freelist entries that might never be usable. This is specially needed
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* when the caller is repeatedly repalloc()'ing a block bigger and bigger;
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* the previous instances of the block were guaranteed to be wasted until
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* AllocSetReset() under the old way.
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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@ -34,7 +42,9 @@
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/*--------------------
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* Chunk freelist k holds chunks of size 1 << (k + ALLOC_MINBITS),
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* for k = 0 .. ALLOCSET_NUM_FREELISTS-2.
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* The last freelist holds all larger chunks.
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* The last freelist holds all larger free chunks. Those chunks come in
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* varying sizes depending on the request size, whereas smaller chunks are
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* coerced to powers of 2 to improve their "recyclability".
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*
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* CAUTION: ALLOC_MINBITS must be large enough so that
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* 1<<ALLOC_MINBITS is at least MAXALIGN,
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@ -51,16 +61,28 @@
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* The first block allocated for an allocset has size ALLOC_MIN_BLOCK_SIZE.
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* Each time we have to allocate another block, we double the block size
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* (if possible, and without exceeding ALLOC_MAX_BLOCK_SIZE), so as to reduce
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* the load on "malloc".
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* the bookkeeping load on malloc().
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*
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* Blocks allocated to hold oversize chunks do not follow this rule, however;
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* they are just however big they need to be.
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* they are just however big they need to be to hold that single chunk.
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* AllocSetAlloc has some freedom about whether to consider a chunk larger
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* than ALLOC_SMALLCHUNK_LIMIT to be "oversize". We require all chunks
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* >= ALLOC_BIGCHUNK_LIMIT to be allocated as single-chunk blocks; those
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* chunks are treated specially by AllocSetFree and AllocSetRealloc. For
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* request sizes between ALLOC_SMALLCHUNK_LIMIT and ALLOC_BIGCHUNK_LIMIT,
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* AllocSetAlloc has discretion whether to put the request into an existing
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* block or make a single-chunk block.
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*
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* We must have ALLOC_MIN_BLOCK_SIZE > ALLOC_SMALLCHUNK_LIMIT and
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* ALLOC_BIGCHUNK_LIMIT > ALLOC_SMALLCHUNK_LIMIT.
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*--------------------
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*/
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#define ALLOC_MIN_BLOCK_SIZE 8192
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#define ALLOC_MIN_BLOCK_SIZE (8 * 1024)
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#define ALLOC_MAX_BLOCK_SIZE (8 * 1024 * 1024)
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#define ALLOC_BIGCHUNK_LIMIT (64 * 1024)
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/* Chunks >= ALLOC_BIGCHUNK_LIMIT are immediately free()d by pfree() */
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#define ALLOC_BLOCKHDRSZ MAXALIGN(sizeof(AllocBlockData))
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#define ALLOC_CHUNKHDRSZ MAXALIGN(sizeof(AllocChunkData))
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@ -104,13 +126,6 @@ AllocSetFreeIndex(Size size)
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* Public routines
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*/
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/*
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* AllocPointerIsValid(pointer)
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* AllocSetIsValid(set)
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*
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* .. are now macros in aset.h -cim 4/27/91
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*/
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/*
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* AllocSetInit
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* Initializes given allocation set.
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@ -141,7 +156,7 @@ AllocSetInit(AllocSet set, AllocMode mode, Size limit)
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/*
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* AllocSetReset
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* Frees memory which is allocated in the given set.
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* Frees all memory which is allocated in the given set.
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*
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* Exceptions:
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* BadArg if set is invalid.
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@ -195,7 +210,7 @@ AllocSetAlloc(AllocSet set, Size size)
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{
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AllocBlock block;
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AllocChunk chunk;
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AllocChunk freeref = NULL;
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AllocChunk priorfree = NULL;
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int fidx;
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Size chunk_size;
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Size blksize;
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@ -212,7 +227,7 @@ AllocSetAlloc(AllocSet set, Size size)
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{
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if (chunk->size >= size)
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break;
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freeref = chunk;
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priorfree = chunk;
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}
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/*
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@ -222,10 +237,10 @@ AllocSetAlloc(AllocSet set, Size size)
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*/
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if (chunk != NULL)
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{
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if (freeref == NULL)
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if (priorfree == NULL)
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set->freelist[fidx] = (AllocChunk) chunk->aset;
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else
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freeref->aset = chunk->aset;
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priorfree->aset = chunk->aset;
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chunk->aset = (void *) set;
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return AllocChunkGetPointer(chunk);
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@ -241,22 +256,23 @@ AllocSetAlloc(AllocSet set, Size size)
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Assert(chunk_size >= size);
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/*
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* If there is enough room in the active allocation block, always
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* allocate the chunk there.
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* If there is enough room in the active allocation block, *and*
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* the chunk is less than ALLOC_BIGCHUNK_LIMIT, put the chunk
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* into the active allocation block.
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*/
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if ((block = set->blocks) != NULL)
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{
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Size have_free = block->endptr - block->freeptr;
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if (have_free < (chunk_size + ALLOC_CHUNKHDRSZ))
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if (have_free < (chunk_size + ALLOC_CHUNKHDRSZ) ||
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chunk_size >= ALLOC_BIGCHUNK_LIMIT)
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block = NULL;
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}
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/*
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* Otherwise, if requested size exceeds smallchunk limit, allocate an
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* entire separate block for this allocation
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*
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* entire separate block for this allocation. In particular, we will
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* always take this path if the requested size exceeds bigchunk limit.
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*/
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if (block == NULL && size > ALLOC_SMALLCHUNK_LIMIT)
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{
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@ -290,7 +306,7 @@ AllocSetAlloc(AllocSet set, Size size)
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}
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/*
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* Time to create a new regular block?
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* Time to create a new regular (multi-chunk) block?
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*/
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if (block == NULL)
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{
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@ -364,7 +380,6 @@ AllocSetAlloc(AllocSet set, Size size)
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void
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AllocSetFree(AllocSet set, AllocPointer pointer)
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{
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int fidx;
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AllocChunk chunk;
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/* AssertArg(AllocSetIsValid(set)); */
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@ -372,10 +387,42 @@ AllocSetFree(AllocSet set, AllocPointer pointer)
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AssertArg(AllocSetContains(set, pointer));
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chunk = AllocPointerGetChunk(pointer);
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fidx = AllocSetFreeIndex(chunk->size);
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chunk->aset = (void *) set->freelist[fidx];
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set->freelist[fidx] = chunk;
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if (chunk->size >= ALLOC_BIGCHUNK_LIMIT)
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{
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/* Big chunks are certain to have been allocated as single-chunk
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* blocks. Find the containing block and return it to malloc().
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*/
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AllocBlock block = set->blocks;
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AllocBlock prevblock = NULL;
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while (block != NULL)
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{
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if (chunk == (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ))
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break;
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prevblock = block;
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block = block->next;
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}
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if (block == NULL)
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elog(ERROR, "AllocSetFree: cannot find block containing chunk");
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/* let's just make sure chunk is the only one in the block */
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Assert(block->freeptr == ((char *) block) +
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(chunk->size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ));
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/* OK, remove block from aset's list and free it */
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if (prevblock == NULL)
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set->blocks = block->next;
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else
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prevblock->next = block->next;
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free(block);
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}
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else
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{
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/* Normal case, put the chunk into appropriate freelist */
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int fidx = AllocSetFreeIndex(chunk->size);
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chunk->aset = (void *) set->freelist[fidx];
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set->freelist[fidx] = chunk;
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}
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}
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/*
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@ -393,7 +440,6 @@ AllocSetFree(AllocSet set, AllocPointer pointer)
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AllocPointer
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AllocSetRealloc(AllocSet set, AllocPointer pointer, Size size)
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{
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AllocPointer newPointer;
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Size oldsize;
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/* AssertArg(AllocSetIsValid(set)); */
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@ -402,23 +448,70 @@ AllocSetRealloc(AllocSet set, AllocPointer pointer, Size size)
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/*
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* Chunk sizes are aligned to power of 2 on AllocSetAlloc(). Maybe the
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* allocated area already is >= the new size.
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*
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* allocated area already is >= the new size. (In particular, we
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* always fall out here if the requested size is a decrease.)
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*/
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oldsize = AllocPointerGetSize(pointer);
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if (oldsize >= size)
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return pointer;
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/* allocate new pointer */
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newPointer = AllocSetAlloc(set, size);
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if (oldsize >= ALLOC_BIGCHUNK_LIMIT)
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{
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/*
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* If the chunk is already >= bigchunk limit, then it must have been
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* allocated as a single-chunk block. Find the containing block and
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* use realloc() to make it bigger with minimum space wastage.
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*/
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AllocChunk chunk = AllocPointerGetChunk(pointer);
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AllocBlock block = set->blocks;
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AllocBlock prevblock = NULL;
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Size blksize;
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/* fill new memory */
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memmove(newPointer, pointer, (oldsize < size) ? oldsize : size);
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while (block != NULL)
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{
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if (chunk == (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ))
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break;
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prevblock = block;
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block = block->next;
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}
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if (block == NULL)
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elog(ERROR, "AllocSetRealloc: cannot find block containing chunk");
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/* let's just make sure chunk is the only one in the block */
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Assert(block->freeptr == ((char *) block) +
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(chunk->size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ));
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/* free old pointer */
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AllocSetFree(set, pointer);
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/* Do the realloc */
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size = MAXALIGN(size);
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blksize = size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
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block = (AllocBlock) realloc(block, blksize);
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if (block == NULL)
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elog(FATAL, "Memory exhausted in AllocSetReAlloc()");
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block->freeptr = block->endptr = ((char *) block) + blksize;
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return newPointer;
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/* Update pointers since block has likely been moved */
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chunk = (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ);
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if (prevblock == NULL)
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set->blocks = block;
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else
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prevblock->next = block;
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chunk->size = size;
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return AllocChunkGetPointer(chunk);
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}
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else
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{
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/* Normal small-chunk case: just do it by brute force. */
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/* allocate new chunk */
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AllocPointer newPointer = AllocSetAlloc(set, size);
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/* transfer existing data (certain to fit) */
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memcpy(newPointer, pointer, oldsize);
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/* free old chunk */
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AllocSetFree(set, pointer);
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return newPointer;
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}
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}
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/*
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@ -15,7 +15,7 @@
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*
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* Copyright (c) 1994, Regents of the University of California
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*
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* $Id: memutils.h,v 1.30 1999/07/15 15:21:41 momjian Exp $
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* $Id: memutils.h,v 1.31 1999/08/24 20:11:19 tgl Exp $
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*
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* NOTES
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* some of the information in this file will be moved to
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@ -101,6 +101,12 @@ extern void OrderedElemPushInto(OrderedElem elem, OrderedSet Set);
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* reallocated. In addition, an allocation set may be reset which
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* will cause all memory allocated within it to be freed.
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*
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* XXX The following material about allocation modes is all OUT OF DATE.
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* aset.c currently implements only one allocation strategy,
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* DynamicAllocMode, and that's the only one anyone ever requests anyway.
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* If we ever did have more strategies, the new ones might or might
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* not look like what is described here...
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*
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* Allocations may occur in four different modes. The mode of
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* allocation does not affect the behavior of allocations except in
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* terms of performance. The allocation mode is set at the time of
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@ -146,7 +152,7 @@ typedef Pointer AllocPointer;
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* Mode of allocation for an allocation set.
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*
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* Note:
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* See above for a description of the various nodes.
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* See above for a description of the various modes.
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*/
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typedef enum AllocMode
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{
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@ -158,23 +164,42 @@ typedef enum AllocMode
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#define DefaultAllocMode DynamicAllocMode
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typedef struct AllocSetData *AllocSet;
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typedef struct AllocBlockData *AllocBlock;
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typedef struct AllocChunkData *AllocChunk;
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/*
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* AllocSet
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* Allocation set.
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*/
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typedef struct AllocSetData
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{
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AllocBlock blocks; /* head of list of blocks in this set */
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#define ALLOCSET_NUM_FREELISTS 8
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AllocChunk freelist[ALLOCSET_NUM_FREELISTS]; /* free chunk lists */
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/* Note: this will change in the future to support other modes */
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} AllocSetData;
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/*
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* AllocBlock
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* Small pieces of memory are taken from bigger blocks of
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* memory with a size aligned to a power of two. These
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* pieces are not free's separately, instead they are reused
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* for the next allocation of a fitting size.
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* An AllocBlock is the unit of memory that is obtained by aset.c
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* from malloc(). It contains one or more AllocChunks, which are
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* the units requested by palloc() and freed by pfree(). AllocChunks
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* cannot be returned to malloc() individually, instead they are put
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* on freelists by pfree() and re-used by the next palloc() that has
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* a matching request size.
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*
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* AllocBlockData is the header data for a block --- the usable space
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* within the block begins at the next alignment boundary.
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*/
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typedef struct AllocBlockData
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{
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struct AllocSetData *aset;
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struct AllocBlockData *next;
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char *freeptr;
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char *endptr;
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AllocSet aset; /* aset that owns this block */
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AllocBlock next; /* next block in aset's blocks list */
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char *freeptr; /* start of free space in this block */
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char *endptr; /* end of space in this block */
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} AllocBlockData;
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typedef AllocBlockData *AllocBlock;
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/*
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* AllocChunk
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* The prefix of each piece of memory in an AllocBlock
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@ -183,26 +208,10 @@ typedef struct AllocChunkData
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{
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/* aset is the owning aset if allocated, or the freelist link if free */
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void *aset;
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/* size is always the chunk size */
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/* size is always the size of the usable space in the chunk */
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Size size;
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} AllocChunkData;
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typedef AllocChunkData *AllocChunk;
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/*
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* AllocSet
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* Allocation set.
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*/
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typedef struct AllocSetData
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{
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struct AllocBlockData *blocks;
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#define ALLOCSET_NUM_FREELISTS 8
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struct AllocChunkData *freelist[ALLOCSET_NUM_FREELISTS];
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/* Note: this will change in the future to support other modes */
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} AllocSetData;
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typedef AllocSetData *AllocSet;
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/*
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* AllocPointerIsValid
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* True iff pointer is valid allocation pointer.
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Reference in New Issue