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Shrink memory contexts struct sizes

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Here we reduce the block size fields in AllocSetContext, GenerationContext
and SlabContext from Size down to uint32.  Ever since c6e0fe1f2, blocks
for non-dedicated palloc chunks can no longer be larger than 1GB, so
there's no need to store the various block size fields as 64-bit values.
32 bits are enough to store 2^30.

Here we also further reduce the memory context struct sizes by getting rid
of the 'keeper' field which stores a pointer to the context's keeper
block.  All the context types which have this field always allocate the
keeper block in the same allocation as the memory context itself, so the
keeper block always comes right at the end of the context struct.  Add
some macros to calculate that address rather than storing it in the
context.

Overall, in AllocSetContext and GenerationContext, this saves 20 bytes on
64-bit builds which for ALLOCSET_SMALL_SIZES can sometimes mean the
difference between having to allocate a 2nd block and storing all the
required allocations on the keeper block alone.  Such contexts are used
in relcache to store cache entries for indexes, of which there can be
a large number in a single backend.

Author: Melih Mutlu
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/CAGPVpCSOW3uJ1QJmsMR9_oE3X7fG_z4q0AoU4R_w+2RzvroPFg@mail.gmail.com
This commit is contained in:
David Rowley
2023-07-17 11:16:56 +12:00
parent 03d1080d8a
commit 2c2eb0d6b2
3 changed files with 60 additions and 48 deletions
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44
src/backend/utils/mmgr/aset.c
View File

@@ -156,11 +156,10 @@ typedef struct AllocSetContext
AllocBlock blocks; /* head of list of blocks in this set */
MemoryChunk *freelist[ALLOCSET_NUM_FREELISTS]; /* free chunk lists */
/* Allocation parameters for this context: */
Size initBlockSize; /* initial block size */
Size maxBlockSize; /* maximum block size */
Size nextBlockSize; /* next block size to allocate */
Size allocChunkLimit; /* effective chunk size limit */
AllocBlock keeper; /* keep this block over resets */
uint32 initBlockSize; /* initial block size */
uint32 maxBlockSize; /* maximum block size */
uint32 nextBlockSize; /* next block size to allocate */
uint32 allocChunkLimit; /* effective chunk size limit */
/* freelist this context could be put in, or -1 if not a candidate: */
int freeListIndex; /* index in context_freelists[], or -1 */
} AllocSetContext;
@@ -241,6 +240,13 @@ typedef struct AllocBlockData
*/
#define MAX_FREE_CONTEXTS 100 /* arbitrary limit on freelist length */
/* Obtain the keeper block for an allocation set */
#define KeeperBlock(set) \
((AllocBlock) (((char *) set) + MAXALIGN(sizeof(AllocSetContext))))
/* Check if the block is the keeper block of the given allocation set */
#define IsKeeperBlock(set, block) ((block) == (KeeperBlock(set)))
typedef struct AllocSetFreeList
{
int num_free; /* current list length */
@@ -417,7 +423,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
name);
((MemoryContext) set)->mem_allocated =
set->keeper->endptr - ((char *) set);
KeeperBlock(set)->endptr - ((char *) set);
return (MemoryContext) set;
}
@@ -453,7 +459,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
*/
/* Fill in the initial block's block header */
block = (AllocBlock) (((char *) set) + MAXALIGN(sizeof(AllocSetContext)));
block = KeeperBlock(set);
block->aset = set;
block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
block->endptr = ((char *) set) + firstBlockSize;
@@ -465,15 +471,13 @@ AllocSetContextCreateInternal(MemoryContext parent,
/* Remember block as part of block list */
set->blocks = block;
/* Mark block as not to be released at reset time */
set->keeper = block;
/* Finish filling in aset-specific parts of the context header */
MemSetAligned(set->freelist, 0, sizeof(set->freelist));
set->initBlockSize = initBlockSize;
set->maxBlockSize = maxBlockSize;
set->nextBlockSize = initBlockSize;
set->initBlockSize = (uint32) initBlockSize;
set->maxBlockSize = (uint32) maxBlockSize;
set->nextBlockSize = (uint32) initBlockSize;
set->freeListIndex = freeListIndex;
/*
@@ -544,7 +548,7 @@ AllocSetReset(MemoryContext context)
#endif
/* Remember keeper block size for Assert below */
keepersize = set->keeper->endptr - ((char *) set);
keepersize = KeeperBlock(set)->endptr - ((char *) set);
/* Clear chunk freelists */
MemSetAligned(set->freelist, 0, sizeof(set->freelist));
@@ -552,13 +556,13 @@ AllocSetReset(MemoryContext context)
block = set->blocks;
/* New blocks list will be just the keeper block */
set->blocks = set->keeper;
set->blocks = KeeperBlock(set);
while (block != NULL)
{
AllocBlock next = block->next;
if (block == set->keeper)
if (IsKeeperBlock(set, block))
{
/* Reset the block, but don't return it to malloc */
char *datastart = ((char *) block) + ALLOC_BLOCKHDRSZ;
@@ -614,7 +618,7 @@ AllocSetDelete(MemoryContext context)
#endif
/* Remember keeper block size for Assert below */
keepersize = set->keeper->endptr - ((char *) set);
keepersize = KeeperBlock(set)->endptr - ((char *) set);
/*
* If the context is a candidate for a freelist, put it into that freelist
@@ -663,14 +667,14 @@ AllocSetDelete(MemoryContext context)
{
AllocBlock next = block->next;
if (block != set->keeper)
if (!IsKeeperBlock(set, block))
context->mem_allocated -= block->endptr - ((char *) block);
#ifdef CLOBBER_FREED_MEMORY
wipe_mem(block, block->freeptr - ((char *) block));
#endif
if (block != set->keeper)
if (!IsKeeperBlock(set, block))
free(block);
block = next;
@@ -1547,7 +1551,7 @@ AllocSetCheck(MemoryContext context)
long nchunks = 0;
bool has_external_chunk = false;
if (set->keeper == block)
if (IsKeeperBlock(set, block))
total_allocated += block->endptr - ((char *) set);
else
total_allocated += block->endptr - ((char *) block);
@@ -1557,7 +1561,7 @@ AllocSetCheck(MemoryContext context)
*/
if (!blk_used)
{
if (set->keeper != block)
if (!IsKeeperBlock(set, block))
elog(WARNING, "problem in alloc set %s: empty block %p",
name, block);
}