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ggml-alloc : make gallocr prefer chunks that allow memory reuse #16788

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Merged
merged 1 commit into from
Oct 26, 2025
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ggml-alloc : make gallocr prefer chunks that allow memory reuse #16788

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15 changes: 11 additions & 4 deletions ggml/src/ggml-alloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -226,16 +226,23 @@ static struct buffer_address ggml_dyn_tallocr_alloc(struct ggml_dyn_tallocr * al
}

if (best_fit_block == -1) {
// no suitable block found, try the last block (this will grow a chunks size)
// no suitable block found, try the last block (this may grow a chunks size)
int64_t best_reuse = INT64_MIN;
for (int c = 0; c < alloc->n_chunks; ++c) {
struct tallocr_chunk * chunk = alloc->chunks[c];
if (chunk->n_free_blocks > 0) {
struct free_block * block = &chunk->free_blocks[chunk->n_free_blocks - 1];
max_avail = MAX(max_avail, block->size);
if (block->size >= size) {
int64_t reuse_factor = chunk->max_size - block->offset - size;
// reuse_factor < 0 : amount of extra memory that needs to be allocated
// reuse_factor = 0 : allocated free space exactly matches tensor size
// reuse_factor > 0 : superfluous memory that will remain unused
bool better_reuse = best_reuse < 0 && reuse_factor > best_reuse;
bool better_fit = reuse_factor >= 0 && reuse_factor < best_reuse;
if (block->size >= size && (better_reuse || better_fit)) {
best_fit_chunk = c;
best_fit_block = chunk->n_free_blocks - 1;
break;
best_reuse = reuse_factor;
}
}
}
Expand Down Expand Up @@ -268,7 +275,7 @@ static struct buffer_address ggml_dyn_tallocr_alloc(struct ggml_dyn_tallocr * al
#ifdef GGML_ALLOCATOR_DEBUG
add_allocated_tensor(alloc, addr, tensor);
size_t cur_max = addr.offset + size;
if (cur_max > alloc->max_size[addr.chunk]) {
if (cur_max > chunk->max_size) {
// sort allocated_tensors by chunk/offset
for (int i = 0; i < 1024; i++) {
for (int j = i + 1; j < 1024; j++) {
Expand Down
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