ggml-alloc.c

#include "ggml-alloc.h"
#include "ggml.h"
#include <assert.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define UNUSED(x) (void)(x)
#define MAX(a, b) ((a) > (b) ? (a) : (b))

//#define GGML_ALLOCATOR_DEBUG

//#define AT_PRINTF printf
#define AT_PRINTF(...) ((void)0)

struct hash_node {
    struct ggml_tensor * t;
    int n_children;
    int n_views;
};

static size_t hash(void * p) {
    return (size_t)p % GGML_GRAPH_HASHTABLE_SIZE;
}

static struct hash_node * hash_get(struct hash_node hash_table[], struct ggml_tensor * t) {
    size_t h = hash(t);

    // linear probing
    size_t i = h;
    while (hash_table[i].t != NULL) {
        if (hash_table[i].t == t) {
            return &hash_table[i];
        }
        i = (i + 1) % GGML_GRAPH_HASHTABLE_SIZE;
        if (i == h) {
            // hash table is full
            GGML_ASSERT(false);
        }
    }

    hash_table[i].t = t;
    return &hash_table[i];
}

// TODO: GGML_PAD ?
static size_t aligned_offset(const void * buffer, size_t offset, size_t alignment) {
    assert(alignment && !(alignment & (alignment - 1))); // power of 2
    size_t align = (alignment - (((uintptr_t)buffer + offset) % alignment)) % alignment;
    return offset + align;
}

struct free_block {
    void * addr;
    size_t size;
};

#define MAX_FREE_BLOCKS 256

struct ggml_allocr {
    void * data;
    size_t size;
    size_t alignment;
    int n_free_blocks;
    struct free_block free_blocks[MAX_FREE_BLOCKS];
    struct hash_node hash_table[GGML_GRAPH_HASHTABLE_SIZE];
    size_t max_size;
    bool measure;

#ifdef GGML_ALLOCATOR_DEBUG
    struct ggml_tensor * allocated_tensors[1024];
#endif
};

#ifdef GGML_ALLOCATOR_DEBUG
static void add_allocated_tensor(struct ggml_allocator * alloc, struct ggml_tensor * tensor) {
    for (int i = 0; i < 1024; i++) {
        if (alloc->allocated_tensors[i] == NULL) {
            alloc->allocated_tensors[i] = tensor;
            return;
        }
    }
    GGML_ASSERT(!"out of allocated_tensors");
}
static void remove_allocated_tensor(struct ggml_allocator * alloc, struct ggml_tensor * tensor) {
    for (int i = 0; i < 1024; i++) {
        if (alloc->allocated_tensors[i] == tensor ||
            (alloc->allocated_tensors[i] != NULL && alloc->allocated_tensors[i]->data == tensor->data)) {
            alloc->allocated_tensors[i] = NULL;
            return;
        }
    }
    printf("tried to free tensor %s not found\n", tensor->name);
    GGML_ASSERT(!"tensor not found");
}
#endif


static size_t ggml_allocator_get_alloc_size(struct ggml_allocr * alloc, struct ggml_tensor * tensor) {
    return ggml_nbytes(tensor);

    UNUSED(alloc);
}

void ggml_allocr_alloc(struct ggml_allocr * alloc, struct ggml_tensor * tensor) {
    size_t size = ggml_allocator_get_alloc_size(alloc, tensor);
    size = aligned_offset(NULL, size, alloc->alignment);

    AT_PRINTF("%s: allocating %s (%zu bytes) - ", __func__, tensor->name, size);

    size_t max_avail = 0;

    // find the best fitting free block
    int best_fit_block = -1;
    size_t best_fit_size = SIZE_MAX;
    for (int i = 0; i < alloc->n_free_blocks; i++) {
        struct free_block * block = &alloc->free_blocks[i];
        max_avail = MAX(max_avail, block->size);
        if (block->size >= size && block->size <= best_fit_size) {
            best_fit_block = i;
            best_fit_size = block->size;
        }
    }

    AT_PRINTF("block %d\n", best_fit_block);

    if (best_fit_block == -1) {
        fprintf(stderr, "%s: not enough space in the buffer (needed %zu, largest block available %zu)\n",
                __func__, size, max_avail);
        GGML_ASSERT(!"not enough space in the buffer");
        return;
    }
    struct free_block * block = &alloc->free_blocks[best_fit_block];
    void * addr = block->addr;
    block->addr = (char*)block->addr + size;
    block->size -= size;
    if (block->size == 0) {
        // remove block if empty
        alloc->n_free_blocks--;
        for (int j = best_fit_block; j < alloc->n_free_blocks; j++) {
            alloc->free_blocks[j] = alloc->free_blocks[j+1];
        }
    }

    tensor->data = addr;

#ifdef GGML_ALLOCATOR_DEBUG
    add_allocated_tensor(alloc, tensor);
    size_t cur_max = (char*)addr - (char*)alloc->data + size;
    if (cur_max > alloc->max_size) {
        printf("max_size = %.2f MB: tensors: ", cur_max / 1024.0 / 1024.0);
        for (int i = 0; i < 1024; i++) {
            if (alloc->allocated_tensors[i]) {
                printf("%s (%.2f MB) ", alloc->allocated_tensors[i]->name, ggml_nbytes(alloc->allocated_tensors[i]) / 1024.0 / 1024.0);
            }
        }
        printf("\n");
    }
#endif

    alloc->max_size = MAX(alloc->max_size, (char*)addr - (char*)alloc->data + size);
}

// this is a very naive implementation, but for our case the number of free blocks should be very small
static void ggml_allocator_free_tensor(struct ggml_allocr * alloc, struct ggml_tensor * tensor) {
    void * ptr = tensor->data;

    if (ptr < alloc->data || (char*)ptr >= (char*)alloc->data + alloc->max_size) {
        // the tensor was not allocated in this buffer
        // this can happen because the graph allocator will try to free weights and other tensors from different buffers
        // the easiest way to deal with this is just to ignore it
        return;
    }

    size_t size = ggml_allocator_get_alloc_size(alloc, tensor);
    size = aligned_offset(NULL, size, alloc->alignment);
    AT_PRINTF("%s: freeing %s (%zu bytes) - n_free_blocks = %d\n", __func__, tensor->name, size, alloc->n_free_blocks);

#ifdef GGML_ALLOCATOR_DEBUG
    remove_allocated_tensor(alloc, tensor);
#endif

    // see if we can merge with an existing block
    for (int i = 0; i < alloc->n_free_blocks; i++) {
        struct free_block * block = &alloc->free_blocks[i];
        // check if ptr is at the end of the block
        if ((char*)block->addr + block->size == ptr) {
            block->size += size;
            // check if we can merge with the next block
            if (i < alloc->n_free_blocks - 1 && (char*)block->addr + block->size == alloc->free_blocks[i+1].addr) {
                block->size += alloc->free_blocks[i+1].size;
                alloc->n_free_blocks--;
                for (int j = i+1; j < alloc->n_free_blocks; j++) {
                    alloc->free_blocks[j] = alloc->free_blocks[j+1];
                }
            }
            return;
        }
        // check if ptr is at the beginning of the block
        if ((char*)ptr + size == block->addr) {
            block->addr = ptr;
            block->size += size;
            // check if we can merge with the previous block
            if (i > 0 && (char*)alloc->free_blocks[i-1].addr + alloc->free_blocks[i-1].size == block->addr) {
                alloc->free_blocks[i-1].size += block->size;
                alloc->n_free_blocks--;
                for (int j = i; j < alloc->n_free_blocks; j++) {
                    alloc->free_blocks[j] = alloc->free_blocks[j+1];
                }
            }
            return;
        }
    }
    // otherwise, add a new block
    GGML_ASSERT(alloc->n_free_blocks < MAX_FREE_BLOCKS && "out of free blocks");
    // insert the new block in the correct position to keep the array sorted by address (to make merging blocks faster)
    int insert_pos = 0;
    while (insert_pos < alloc->n_free_blocks && alloc->free_blocks[insert_pos].addr < ptr) {
        insert_pos++;
    }
    // shift all blocks from insert_pos onward to make room for the new block
    for (int i = alloc->n_free_blocks; i > insert_pos; i--) {
        alloc->free_blocks[i] = alloc->free_blocks[i-1];
    }
    // insert the new block
    alloc->free_blocks[insert_pos].addr = ptr;
    alloc->free_blocks[insert_pos].size = size;
    alloc->n_free_blocks++;
}

void ggml_allocr_reset(struct ggml_allocr * alloc) {
    alloc->n_free_blocks = 1;
    size_t align_offset = aligned_offset(alloc->data, 0, alloc->alignment);
    alloc->free_blocks[0].addr = (char *)alloc->data + align_offset;
    alloc->free_blocks[0].size = alloc->size - align_offset;
}

struct ggml_allocr * ggml_allocr_new(void * data, size_t size, size_t alignment) {
    struct ggml_allocr * alloc = (struct ggml_allocr *)malloc(sizeof(struct ggml_allocr) /* + n_free_blocks * sizeof(struct free_block) */);

    *alloc = (struct ggml_allocr){
        /*.data          = */ data,
        /*.size          = */ size,
        /*.alignment     = */ alignment,
        /*.n_free_blocks = */ 0,
        /*.free_blocks   = */ {{0}},
        /*.hash_table    = */ {{0}},
        /*.max_size      = */ 0,
        /*.measure       = */ false,
#ifdef GGML_ALLOCATOR_DEBUG
        /*.allocated_tensors = */ = {0},
#endif
    };

    ggml_allocr_reset(alloc);

    return alloc;
}

// address and size of the buffer when measuring
// it needs to be large enough to fit all the tensors, but it cannot overlap with other existing buffers
static void * const MEASURE_BASE_ADDR = (void *) 0x1000;
static const size_t MEASURE_MAX_SIZE  = 1ULL<<40; // 1 TB

struct ggml_allocr * ggml_allocr_new_measure(size_t alignment) {
    struct ggml_allocr * alloc = (struct ggml_allocr *)malloc(sizeof(struct ggml_allocr) /* + n_free_blocks * sizeof(struct free_block) */);

    *alloc = (struct ggml_allocr){
        /*.data          = */ MEASURE_BASE_ADDR,
        /*.size          = */ MEASURE_MAX_SIZE,
        /*.alignment     = */ alignment,
        /*.n_free_blocks = */ 0,
        /*.free_blocks   = */ {{0}},
        /*.hash_table    = */ {{0}},
        /*.max_size      = */ 0,
        /*.measure       = */ true,
#ifdef GGML_ALLOCATOR_DEBUG
        /*.allocated_tensors = */ = {0},
#endif
    };

    ggml_allocr_reset(alloc);

    return alloc;
}

void ggml_allocr_free(struct ggml_allocr * alloc) {
    free(alloc);
}

bool ggml_allocr_is_measure(struct ggml_allocr * alloc) {
    return alloc->measure;
}

//////////// compute graph allocator

static bool ggml_is_view(struct ggml_tensor * t) {
    return t->op == GGML_OP_RESHAPE || t->op == GGML_OP_VIEW || t->op == GGML_OP_TRANSPOSE ||
           t->op == GGML_OP_PERMUTE || t->op == GGML_OP_CPY;
}

static bool ggml_are_same_layout(const struct ggml_tensor * a, const struct ggml_tensor * b) {
    if (a->type != b->type) {
        return false;
    }
    for (int i = 0; i < GGML_MAX_DIMS; i++) {
        if (a->ne[i] != b->ne[i]) {
            return false;
        }
        if (a->nb[i] != b->nb[i]) {
            return false;
        }
    }
    return true;
}

static struct ggml_tensor * get_view_parent(struct ggml_tensor * t) {
    switch (t->op) {
        case GGML_OP_PERMUTE:
        case GGML_OP_RESHAPE:
        case GGML_OP_TRANSPOSE:
        case GGML_OP_VIEW:
            return t->src[0];
        case GGML_OP_CPY:
            return t->src[1];
        default:
            return NULL;
    }
}

static struct ggml_tensor * get_view_source(struct ggml_tensor * t) {
    struct ggml_tensor * parent = t;
    do {
        parent = get_view_parent(parent);
    } while (ggml_is_view(parent));
    return parent;
}

static bool ggml_op_can_inplace(enum ggml_op op) {
    switch (op) {
        case GGML_OP_SCALE:
        case GGML_OP_DIAG_MASK_ZERO:
        case GGML_OP_DIAG_MASK_INF:
        case GGML_OP_ADD:
        case GGML_OP_ADD1:
        case GGML_OP_ACC:
        case GGML_OP_SUB:
        case GGML_OP_MUL:
        case GGML_OP_DIV:
        case GGML_OP_SQR:
        case GGML_OP_SQRT:
        case GGML_OP_LOG:
        case GGML_OP_UNARY:
        case GGML_OP_ROPE:
        case GGML_OP_RMS_NORM:
        case GGML_OP_SET:
        case GGML_OP_SOFT_MAX:
        case GGML_OP_CONT:
            return true;

        default:
            return false;
    }
}

static void allocate_node(struct ggml_allocr * alloc, struct ggml_tensor * node) {
    struct hash_node * ht = alloc->hash_table;
    if (node->data == NULL) {
        if (ggml_is_view(node)) {
            size_t offset;
            switch(node->op) {
                case GGML_OP_VIEW:
                    memcpy(&offset, node->op_params, sizeof(size_t));
                    node->data = (char *) node->src[0]->data + offset;
                    break;
                case GGML_OP_PERMUTE:
                case GGML_OP_RESHAPE:
                case GGML_OP_TRANSPOSE:
                    node->data = node->src[0]->data;
                    break;
                case GGML_OP_CPY:
                    node->data = node->src[1]->data;
                    break;
                default:
                    GGML_ASSERT(!"unknown view op");
                    break;
            }
        } else {
            // see if we can reuse a parent's buffer (inplace)
            if (ggml_op_can_inplace(node->op)) {
                for (int i = 0; i < GGML_MAX_SRC; i++) {
                    struct ggml_tensor * parent = node->src[i];
                    if (parent == NULL) {
                        break;
                    }
                    struct hash_node * p_hn = hash_get(ht, parent);
                    if (parent->data != NULL && p_hn->n_children == 1 && p_hn->n_views == 0 && ggml_are_same_layout(node, parent)) {
                        if (ggml_is_view(parent)) {
                            struct ggml_tensor * view_src = get_view_source(parent);
                            struct hash_node * view_src_hn = hash_get(ht, view_src);
                            if (view_src_hn->n_views == 1 && view_src_hn->n_children == 0 && view_src->data == parent->data) {
                                // TODO: the offset of the view parent must be kept to ensure that the op doesn't overwrite
                                // the parent's data that it will need later (same layout requirement). the problem is that then
                                // we cannot free the tensor because the original address of the allocation is lost.
                                // adding a view_src pointer to the tensor would solve this and simplify the code dealing with views
                                // for now, we only reuse the parent's data if the offset is zero (view_src->data == parent->data)
                                AT_PRINTF("reusing view parent %s (%s) for %s\n", parent->name, view_src->name, node->name);
                                node->data = parent->data;
                                return;
                            }
                        }
                        else {
                            AT_PRINTF("reusing parent %s for %s\n", parent->name, node->name);
                            node->data = parent->data;
                        }
                        return;
                    }
                }
            }
            ggml_allocr_alloc(alloc, node);
        }
    }
}

static size_t ggml_allocator_alloc_graph_tensors_n(
    struct ggml_allocr * alloc,
    struct ggml_cgraph ** graphs, int n_graphs,
    struct ggml_tensor *** inputs, struct ggml_tensor *** outputs) {

    // reset hash table
    struct hash_node * ht = alloc->hash_table;
    memset(ht, 0, sizeof(struct hash_node) * GGML_GRAPH_HASHTABLE_SIZE);

    // count number of children and views
    for (int g = 0; g < n_graphs; g++) {
        struct ggml_cgraph * gf = graphs[g];
        for (int i = 0; i < gf->n_nodes; i++) {
            struct ggml_tensor * node = gf->nodes[i];

            if (ggml_is_view(node)) {
                struct ggml_tensor * view_src = get_view_source(node);
                hash_get(ht, view_src)->n_views += 1;
            }

            for (int j = 0; j < GGML_MAX_SRC; j++) {
                struct ggml_tensor * parent = node->src[j];
                if (parent == NULL) {
                    break;
                }
                hash_get(ht, parent)->n_children += 1;
            }
        }
    }

    // allocate tensors
    for (int g = 0; g < n_graphs; g++) {
        struct ggml_cgraph * gf = graphs[g];
        AT_PRINTF("####### graph %d/%d\n", g, n_graphs);
        // graph inputs are allocated first to ensure that they are not overwritten by each other
        if (inputs != NULL && inputs[g] != NULL) {
            for (int i = 0; inputs[g][i] != NULL; i++) {
                struct ggml_tensor * input = inputs[g][i];
                AT_PRINTF("input: %s\n", input->name);
                allocate_node(alloc, input);
            }
        }
        for (int i = 0; i < gf->n_nodes; i++) {
            struct ggml_tensor * node = gf->nodes[i];

            // allocate parents (leafs)
            for (int j = 0; j < GGML_MAX_SRC; j++) {
                struct ggml_tensor * parent = node->src[j];
                if (parent == NULL) {
                    break;
                }
                allocate_node(alloc, parent);
            }

            // allocate node
            allocate_node(alloc, node);

            AT_PRINTF("exec: %s (%s) <= ", ggml_op_name(node->op), node->name);
            for (int j = 0; j < GGML_MAX_SRC; j++) {
                struct ggml_tensor * parent = node->src[j];
                if (parent == NULL) {
                    break;
                }
                AT_PRINTF("%s", parent->name);
                if (j < GGML_MAX_SRC - 1 && node->src[j + 1] != NULL) {
                    AT_PRINTF(", ");
                }
            }
            AT_PRINTF("\n");

            // update parents
            for (int j = 0; j < GGML_MAX_SRC; j++) {
                struct ggml_tensor * parent = node->src[j];
                if (parent == NULL) {
                    break;
                }
                struct hash_node * p_hn = hash_get(ht, parent);
                p_hn->n_children -= 1;

                //AT_PRINTF("parent %s: %d children, %d views\n", parent->name, parent->n_children, parent->n_views);

                if (p_hn->n_children == 0 && p_hn->n_views == 0) {
                    if (ggml_is_view(parent)) {
                        struct ggml_tensor * view_src = get_view_source(parent);
                        struct hash_node * view_src_hn = hash_get(ht, view_src);
                        view_src_hn->n_views -= 1;
                        AT_PRINTF("view_src %s: %d children, %d views\n", view_src->name, view_src->n_children, view_src->n_views);
                        if (view_src_hn->n_views == 0 && view_src_hn->n_children == 0 && view_src->data != node->data) {
                            ggml_allocator_free_tensor(alloc, view_src);
                        }
                    }
                    else {
                        if (parent->data != node->data) {
                            ggml_allocator_free_tensor(alloc, parent);
                        }
                    }
                }
            }
            AT_PRINTF("\n");
        }
        // free graph outputs here that wouldn't be freed otherwise because they have no children
        if (outputs != NULL && outputs[g] != NULL) {
            for (int i = 0; outputs[g][i] != NULL; i++) {
                struct ggml_tensor * output = outputs[g][i];
                AT_PRINTF("output: %s\n", output->name);
                ggml_allocator_free_tensor(alloc, output);
            }
        }
    }

    return alloc->max_size;
}

size_t ggml_allocr_alloc_graph(struct ggml_allocr * alloc, struct ggml_cgraph * graph) {
    return ggml_allocator_alloc_graph_tensors_n(alloc, &graph, 1, NULL, NULL);
}