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Commit2b67dc5

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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 enlargedwith repalloc(), translate the operation into a realloc() so as tominimize memory usage. Of course, these large chunks still get freedautomatically if the alloc set is reset.I have set ALLOC_BIGCHUNK_LIMIT at 64K for now, but perhaps anothersize would be better?
1 parent1b81fd7 commit2b67dc5

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2 files changed

+171
-69
lines changed

2 files changed

+171
-69
lines changed

‎src/backend/utils/mmgr/aset.c‎

Lines changed: 133 additions & 40 deletions
Original file line numberDiff line numberDiff line change
@@ -7,18 +7,26 @@
77
*
88
*
99
* IDENTIFICATION
10-
* $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.20 1999/07/17 20:18:13 momjian Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.21 1999/08/24 20:11:17 tgl Exp $
1111
*
1212
* NOTE:
1313
*This is a new (Feb. 05, 1999) implementation of the allocation set
1414
*routines. AllocSet...() does not use OrderedSet...() any more.
1515
*Instead it manages allocations in a block pool by itself, combining
16-
*many small allocations in a few bigger blocks. AllocSetFree()does
17-
*never free() memory really. It just add's the free'd area to some
16+
*many small allocations in a few bigger blocks. AllocSetFree()normally
17+
*doesn't free() memory really. It just add's the free'd area to some
1818
*list for later reuse by AllocSetAlloc(). All memory blocks are free()'d
1919
*at once on AllocSetReset(), which happens when the memory context gets
2020
*destroyed.
2121
*Jan Wieck
22+
*
23+
*Performance improvement from Tom Lane, 8/99: for extremely large request
24+
*sizes, we do want to be able to give the memory back to free() as soon
25+
*as it is pfree()'d. Otherwise we risk tying up a lot of memory in
26+
*freelist entries that might never be usable. This is specially needed
27+
*when the caller is repeatedly repalloc()'ing a block bigger and bigger;
28+
*the previous instances of the block were guaranteed to be wasted until
29+
*AllocSetReset() under the old way.
2230
*-------------------------------------------------------------------------
2331
*/
2432
#include"postgres.h"
@@ -34,7 +42,9 @@
3442
/*--------------------
3543
* Chunk freelist k holds chunks of size 1 << (k + ALLOC_MINBITS),
3644
* for k = 0 .. ALLOCSET_NUM_FREELISTS-2.
37-
* The last freelist holds all larger chunks.
45+
* The last freelist holds all larger free chunks. Those chunks come in
46+
* varying sizes depending on the request size, whereas smaller chunks are
47+
* coerced to powers of 2 to improve their "recyclability".
3848
*
3949
* CAUTION: ALLOC_MINBITS must be large enough so that
4050
* 1<<ALLOC_MINBITS is at least MAXALIGN,
@@ -51,16 +61,28 @@
5161
* The first block allocated for an allocset has size ALLOC_MIN_BLOCK_SIZE.
5262
* Each time we have to allocate another block, we double the block size
5363
* (if possible, and without exceeding ALLOC_MAX_BLOCK_SIZE), so as to reduce
54-
* the load on"malloc".
64+
* thebookkeepingload on malloc().
5565
*
5666
* Blocks allocated to hold oversize chunks do not follow this rule, however;
57-
* they are just however big they need to be.
67+
* they are just however big they need to be to hold that single chunk.
68+
* AllocSetAlloc has some freedom about whether to consider a chunk larger
69+
* than ALLOC_SMALLCHUNK_LIMIT to be "oversize". We require all chunks
70+
* >= ALLOC_BIGCHUNK_LIMIT to be allocated as single-chunk blocks; those
71+
* chunks are treated specially by AllocSetFree and AllocSetRealloc. For
72+
* request sizes between ALLOC_SMALLCHUNK_LIMIT and ALLOC_BIGCHUNK_LIMIT,
73+
* AllocSetAlloc has discretion whether to put the request into an existing
74+
* block or make a single-chunk block.
75+
*
76+
* We must have ALLOC_MIN_BLOCK_SIZE > ALLOC_SMALLCHUNK_LIMIT and
77+
* ALLOC_BIGCHUNK_LIMIT > ALLOC_SMALLCHUNK_LIMIT.
5878
*--------------------
5979
*/
6080

61-
#defineALLOC_MIN_BLOCK_SIZE8192
81+
#defineALLOC_MIN_BLOCK_SIZE(8 * 1024)
6282
#defineALLOC_MAX_BLOCK_SIZE(8 * 1024 * 1024)
6383

84+
#defineALLOC_BIGCHUNK_LIMIT(64 * 1024)
85+
/* Chunks >= ALLOC_BIGCHUNK_LIMIT are immediately free()d by pfree() */
6486

6587
#defineALLOC_BLOCKHDRSZMAXALIGN(sizeof(AllocBlockData))
6688
#defineALLOC_CHUNKHDRSZMAXALIGN(sizeof(AllocChunkData))
@@ -104,13 +126,6 @@ AllocSetFreeIndex(Size size)
104126
* Public routines
105127
*/
106128

107-
/*
108-
*AllocPointerIsValid(pointer)
109-
*AllocSetIsValid(set)
110-
*
111-
*.. are now macros in aset.h -cim 4/27/91
112-
*/
113-
114129
/*
115130
* AllocSetInit
116131
*Initializes given allocation set.
@@ -141,7 +156,7 @@ AllocSetInit(AllocSet set, AllocMode mode, Size limit)
141156

142157
/*
143158
* AllocSetReset
144-
*Frees memory which is allocated in the given set.
159+
*Freesallmemory which is allocated in the given set.
145160
*
146161
* Exceptions:
147162
*BadArg if set is invalid.
@@ -195,7 +210,7 @@ AllocSetAlloc(AllocSet set, Size size)
195210
{
196211
AllocBlockblock;
197212
AllocChunkchunk;
198-
AllocChunkfreeref=NULL;
213+
AllocChunkpriorfree=NULL;
199214
intfidx;
200215
Sizechunk_size;
201216
Sizeblksize;
@@ -212,7 +227,7 @@ AllocSetAlloc(AllocSet set, Size size)
212227
{
213228
if (chunk->size >=size)
214229
break;
215-
freeref=chunk;
230+
priorfree=chunk;
216231
}
217232

218233
/*
@@ -222,10 +237,10 @@ AllocSetAlloc(AllocSet set, Size size)
222237
*/
223238
if (chunk!=NULL)
224239
{
225-
if (freeref==NULL)
240+
if (priorfree==NULL)
226241
set->freelist[fidx]= (AllocChunk)chunk->aset;
227242
else
228-
freeref->aset=chunk->aset;
243+
priorfree->aset=chunk->aset;
229244

230245
chunk->aset= (void*)set;
231246
returnAllocChunkGetPointer(chunk);
@@ -241,22 +256,23 @@ AllocSetAlloc(AllocSet set, Size size)
241256
Assert(chunk_size >=size);
242257

243258
/*
244-
* If there is enough room in the active allocation block, always
245-
* allocate the chunk there.
259+
* If there is enough room in the active allocation block, *and*
260+
* the chunk is less than ALLOC_BIGCHUNK_LIMIT, put the chunk
261+
* into the active allocation block.
246262
*/
247-
248263
if ((block=set->blocks)!=NULL)
249264
{
250265
Sizehave_free=block->endptr-block->freeptr;
251266

252-
if (have_free< (chunk_size+ALLOC_CHUNKHDRSZ))
267+
if (have_free< (chunk_size+ALLOC_CHUNKHDRSZ)||
268+
chunk_size >=ALLOC_BIGCHUNK_LIMIT)
253269
block=NULL;
254270
}
255271

256272
/*
257273
* Otherwise, if requested size exceeds smallchunk limit, allocate an
258-
* entire separate block for this allocation
259-
*
274+
* entire separate block for this allocation. In particular, we will
275+
* always take this path if the requested size exceeds bigchunk limit.
260276
*/
261277
if (block==NULL&&size>ALLOC_SMALLCHUNK_LIMIT)
262278
{
@@ -290,7 +306,7 @@ AllocSetAlloc(AllocSet set, Size size)
290306
}
291307

292308
/*
293-
* Time to create a new regular block?
309+
* Time to create a new regular(multi-chunk)block?
294310
*/
295311
if (block==NULL)
296312
{
@@ -364,18 +380,49 @@ AllocSetAlloc(AllocSet set, Size size)
364380
void
365381
AllocSetFree(AllocSetset,AllocPointerpointer)
366382
{
367-
intfidx;
368383
AllocChunkchunk;
369384

370385
/* AssertArg(AllocSetIsValid(set)); */
371386
/* AssertArg(AllocPointerIsValid(pointer)); */
372387
AssertArg(AllocSetContains(set,pointer));
373388

374389
chunk=AllocPointerGetChunk(pointer);
375-
fidx=AllocSetFreeIndex(chunk->size);
376390

377-
chunk->aset= (void*)set->freelist[fidx];
378-
set->freelist[fidx]=chunk;
391+
if (chunk->size >=ALLOC_BIGCHUNK_LIMIT)
392+
{
393+
/* Big chunks are certain to have been allocated as single-chunk
394+
* blocks. Find the containing block and return it to malloc().
395+
*/
396+
AllocBlockblock=set->blocks;
397+
AllocBlockprevblock=NULL;
398+
399+
while (block!=NULL)
400+
{
401+
if (chunk== (AllocChunk) (((char*)block)+ALLOC_BLOCKHDRSZ))
402+
break;
403+
prevblock=block;
404+
block=block->next;
405+
}
406+
if (block==NULL)
407+
elog(ERROR,"AllocSetFree: cannot find block containing chunk");
408+
/* let's just make sure chunk is the only one in the block */
409+
Assert(block->freeptr== ((char*)block)+
410+
(chunk->size+ALLOC_BLOCKHDRSZ+ALLOC_CHUNKHDRSZ));
411+
/* OK, remove block from aset's list and free it */
412+
if (prevblock==NULL)
413+
set->blocks=block->next;
414+
else
415+
prevblock->next=block->next;
416+
free(block);
417+
}
418+
else
419+
{
420+
/* Normal case, put the chunk into appropriate freelist */
421+
intfidx=AllocSetFreeIndex(chunk->size);
422+
423+
chunk->aset= (void*)set->freelist[fidx];
424+
set->freelist[fidx]=chunk;
425+
}
379426
}
380427

381428
/*
@@ -393,7 +440,6 @@ AllocSetFree(AllocSet set, AllocPointer pointer)
393440
AllocPointer
394441
AllocSetRealloc(AllocSetset,AllocPointerpointer,Sizesize)
395442
{
396-
AllocPointernewPointer;
397443
Sizeoldsize;
398444

399445
/* AssertArg(AllocSetIsValid(set)); */
@@ -402,23 +448,70 @@ AllocSetRealloc(AllocSet set, AllocPointer pointer, Size size)
402448

403449
/*
404450
* Chunk sizes are aligned to power of 2 on AllocSetAlloc(). Maybe the
405-
* allocated area already is >= the new size.
406-
*
451+
* allocated area already is >= the new size. (In particular, we
452+
* always fall out here if the requested size is a decrease.)
407453
*/
408454
oldsize=AllocPointerGetSize(pointer);
409455
if (oldsize >=size)
410456
returnpointer;
411457

412-
/* allocate new pointer */
413-
newPointer=AllocSetAlloc(set,size);
458+
if (oldsize >=ALLOC_BIGCHUNK_LIMIT)
459+
{
460+
/*
461+
* If the chunk is already >= bigchunk limit, then it must have been
462+
* allocated as a single-chunk block. Find the containing block and
463+
* use realloc() to make it bigger with minimum space wastage.
464+
*/
465+
AllocChunkchunk=AllocPointerGetChunk(pointer);
466+
AllocBlockblock=set->blocks;
467+
AllocBlockprevblock=NULL;
468+
Sizeblksize;
414469

415-
/* fill new memory */
416-
memmove(newPointer,pointer, (oldsize<size) ?oldsize :size);
470+
while (block!=NULL)
471+
{
472+
if (chunk== (AllocChunk) (((char*)block)+ALLOC_BLOCKHDRSZ))
473+
break;
474+
prevblock=block;
475+
block=block->next;
476+
}
477+
if (block==NULL)
478+
elog(ERROR,"AllocSetRealloc: cannot find block containing chunk");
479+
/* let's just make sure chunk is the only one in the block */
480+
Assert(block->freeptr== ((char*)block)+
481+
(chunk->size+ALLOC_BLOCKHDRSZ+ALLOC_CHUNKHDRSZ));
482+
483+
/* Do the realloc */
484+
size=MAXALIGN(size);
485+
blksize=size+ALLOC_BLOCKHDRSZ+ALLOC_CHUNKHDRSZ;
486+
block= (AllocBlock)realloc(block,blksize);
487+
if (block==NULL)
488+
elog(FATAL,"Memory exhausted in AllocSetReAlloc()");
489+
block->freeptr=block->endptr= ((char*)block)+blksize;
417490

418-
/* free old pointer */
419-
AllocSetFree(set,pointer);
491+
/* Update pointers since block has likely been moved */
492+
chunk= (AllocChunk) (((char*)block)+ALLOC_BLOCKHDRSZ);
493+
if (prevblock==NULL)
494+
set->blocks=block;
495+
else
496+
prevblock->next=block;
497+
chunk->size=size;
498+
returnAllocChunkGetPointer(chunk);
499+
}
500+
else
501+
{
502+
/* Normal small-chunk case: just do it by brute force. */
503+
504+
/* allocate new chunk */
505+
AllocPointernewPointer=AllocSetAlloc(set,size);
506+
507+
/* transfer existing data (certain to fit) */
508+
memcpy(newPointer,pointer,oldsize);
420509

421-
returnnewPointer;
510+
/* free old chunk */
511+
AllocSetFree(set,pointer);
512+
513+
returnnewPointer;
514+
}
422515
}
423516

424517
/*

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