From 728b0aa290ce2bc1639563e2dfd05fe6d8d6e7f2 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 23 Jan 2001 01:01:36 +0000
Subject: [PATCH] Improve realloc() per idea from Karel Zak --- if chunk to be
enlarged is at end of its block, maybe we can enlarge it in-place.
---
src/backend/utils/mmgr/aset.c | 54 +++++++++++++++++++++++++++++++++--
1 file changed, 52 insertions(+), 2 deletions(-)
diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index 5c0cf307453..c78008824b5 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -11,7 +11,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.37 2001/01/12 21:54:01 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.38 2001/01/23 01:01:36 tgl Exp $
*
* NOTE:
* This is a new (Feb. 05, 1999) implementation of the allocation set
@@ -879,10 +879,60 @@ AllocSetRealloc(MemoryContext context, void *pointer, Size size)
}
else
{
+ /*
+ * Small-chunk case. If the chunk is the last one in its block,
+ * there might be enough free space after it that we can just
+ * enlarge the chunk in-place. It's relatively painful to find
+ * the containing block in the general case, but we can detect
+ * last-ness quite cheaply for the typical case where the chunk
+ * is in the active (topmost) allocation block. (At least with
+ * the regression tests and code as of 1/2001, realloc'ing the last
+ * chunk of a non-topmost block hardly ever happens, so it's not
+ * worth scanning the block list to catch that case.)
+ *
+ * NOTE: must be careful not to create a chunk of a size that
+ * AllocSetAlloc would not create, else we'll get confused later.
+ */
+ AllocPointer newPointer;
+
+ if (size <= ALLOC_CHUNK_LIMIT)
+ {
+ AllocBlock block = set->blocks;
+ char *chunk_end;
+
+ chunk_end = (char *) chunk + (oldsize + ALLOC_CHUNKHDRSZ);
+ if (chunk_end == block->freeptr)
+ {
+ /* OK, it's last in block ... is there room? */
+ Size freespace = block->endptr - block->freeptr;
+ int fidx;
+ Size newsize;
+ Size delta;
+
+ fidx = AllocSetFreeIndex(size);
+ newsize = 1 << (fidx + ALLOC_MINBITS);
+ Assert(newsize >= oldsize);
+ delta = newsize - oldsize;
+ if (freespace >= delta)
+ {
+ /* Yes, so just enlarge the chunk. */
+ block->freeptr += delta;
+ chunk->size += delta;
+#ifdef MEMORY_CONTEXT_CHECKING
+ chunk->requested_size = size;
+ /* set mark to catch clobber of "unused" space */
+ if (size < chunk->size)
+ ((char *) pointer)[size] = 0x7E;
+#endif
+ return pointer;
+ }
+ }
+ }
+
/* Normal small-chunk case: just do it by brute force. */
/* allocate new chunk */
- AllocPointer newPointer = AllocSetAlloc((MemoryContext) set, size);
+ newPointer = AllocSetAlloc((MemoryContext) set, size);
/* transfer existing data (certain to fit) */
memcpy(newPointer, pointer, oldsize);
--
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