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PyObject_Realloc(): If a small block is shrinking, bite the expense of

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copying it if at least 25% of the input block can be reclaimed.
This commit is contained in:
Tim Peters 2002-05-02 20:19:34 +00:00
parent edbffc1725
commit 4ce71f77c3
1 changed files with 16 additions and 5 deletions
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21
Objects/obmalloc.c
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@ -793,11 +793,22 @@ PyObject_Realloc(void *p, size_t nbytes)
if (ADDRESS_IN_RANGE(p, pool->arenaindex)) {
/* We're in charge of this block */
size = INDEX2SIZE(pool->szidx);
if (size >= nbytes)
/* Don't bother if a smaller size was requested. */
return p;
/* We need more memory. */
assert(nbytes != 0);
if (nbytes <= size) {
/* The block is staying the same or shrinking. If
* it's shrinking, there's a tradeoff: it costs
* cycles to copy the block to a smaller size class,
* but it wastes memory not to copy it. The
* compromise here is to copy on shrink only if at
* least 25% of size can be shaved off.
*/
if (4 * nbytes > 3 * size) {
/* It's the same,
* or shrinking and new/old > 3/4.
*/
return p;
}
size = nbytes;
}
bp = PyObject_Malloc(nbytes);
if (bp != NULL) {
memcpy(bp, p, size);