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py: Fix GC realloc issue, where memory chunks were never shrunk.

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Previously, a realloc to a smaller memory chunk size would not free the
unused blocks in the tail of the chunk.
This commit is contained in:
Damien George 2014-10-15 18:24:47 +00:00
parent 4859edb95b
commit 9b0b373e5e
1 changed files with 19 additions and 13 deletions
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32
py/gc.c
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@ -567,22 +567,28 @@ void *gc_realloc(void *ptr_in, mp_uint_t n_bytes) {
// compute number of new blocks that are requested
mp_uint_t new_blocks = (n_bytes + BYTES_PER_BLOCK - 1) / BYTES_PER_BLOCK;
// get the number of consecutive tail blocks and
// the number of free blocks after last tail block
// stop if we reach (or are at) end of heap
// Get the total number of consecutive blocks that are already allocated to
// this chunk of memory, and then count the number of free blocks following
// it. Stop if we reach the end of the heap, or if we find enough extra
// free blocks to satisfy the realloc. Note that we need to compute the
// total size of the existing memory chunk so we can correctly and
// efficiently shrink it (see below for shrinking code).
mp_uint_t n_free = 0;
mp_uint_t n_blocks = 1; // counting HEAD block
mp_uint_t max_block = gc_alloc_table_byte_len * BLOCKS_PER_ATB;
while (block + n_blocks + n_free < max_block) {
if (n_blocks + n_free >= new_blocks) {
// stop as soon as we find enough blocks for n_bytes
break;
for (mp_uint_t bl = block + n_blocks; bl < max_block; bl++) {
byte block_type = ATB_GET_KIND(bl);
if (block_type == AT_TAIL) {
n_blocks++;
continue;
}
byte block_type = ATB_GET_KIND(block + n_blocks + n_free);
switch (block_type) {
case AT_FREE: n_free++; continue;
case AT_TAIL: n_blocks++; continue;
case AT_MARK: assert(0);
if (block_type == AT_FREE) {
n_free++;
if (n_blocks + n_free >= new_blocks) {
// stop as soon as we find enough blocks for n_bytes
break;
}
continue;
}
break;
}
@ -595,7 +601,7 @@ void *gc_realloc(void *ptr_in, mp_uint_t n_bytes) {
// check if we can shrink the allocated area
if (new_blocks < n_blocks) {
// free unneeded tail blocks
for (mp_uint_t bl = block + new_blocks; ATB_GET_KIND(bl) == AT_TAIL; bl++) {
for (mp_uint_t bl = block + new_blocks, count = n_blocks - new_blocks; count > 0; bl++, count--) {
ATB_ANY_TO_FREE(bl);
}