mem-pool: add life cycle management functions

Add initialization and discard functions to mem_pool type. As the memory allocated by mem_pool can now be freed, we also track the large allocations. If the there are existing mp_blocks in the mem_poo's linked list of mp_blocksl, then the mp_block for a large allocation is inserted behind the head block. This is because only the head mp_block is considered when searching for availble space. This results in the following desirable properties: 1) The mp_block allocated for the large request will not be included not included in the search for available in future requests, the large mp_block is sized for the specific request and does not contain any spare space. 2) The head mp_block will not bumped from considation for future memory requests just because a request for a large chunk of memory came in. These changes are in preparation for a future commit that will utilize creating and discarding memory pool. Signed-off-by: Jameson Miller <jamill@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Jameson Miller committed Jul 2, 2018 at 19:49 UTC 158dfeff3dc1d155b84e68b265a9b6c265717e1e
2 files changed +61 -8
mem-pool.c
+51 -8
@@ -5,20 +5,65 @@
5 #include "cache.h"
6 #include "mem-pool.h"
7
8 -static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
8 +#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);
9 +
10 +/*
11 + * Allocate a new mp_block and insert it after the block specified in
12 + * `insert_after`. If `insert_after` is NULL, then insert block at the
13 + * head of the linked list.
14 + */
15 +static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc, struct mp_block *insert_after)
16 {
17 struct mp_block *p;
18
19 mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
20 p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
14 - p->next_block = mem_pool->mp_block;
21 +
22 p->next_free = (char *)p->space;
23 p->end = p->next_free + block_alloc;
17 - mem_pool->mp_block = p;
24 +
25 + if (insert_after) {
26 + p->next_block = insert_after->next_block;
27 + insert_after->next_block = p;
28 + } else {
29 + p->next_block = mem_pool->mp_block;
30 + mem_pool->mp_block = p;
31 + }
32
33 return p;
34 }
35
36 +void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
37 +{
38 + struct mem_pool *pool;
39 +
40 + if (*mem_pool)
41 + return;
42 +
43 + pool = xcalloc(1, sizeof(*pool));
44 +
45 + pool->block_alloc = BLOCK_GROWTH_SIZE;
46 +
47 + if (initial_size > 0)
48 + mem_pool_alloc_block(pool, initial_size, NULL);
49 +
50 + *mem_pool = pool;
51 +}
52 +
53 +void mem_pool_discard(struct mem_pool *mem_pool)
54 +{
55 + struct mp_block *block, *block_to_free;
56 +
57 + while ((block = mem_pool->mp_block))
58 + {
59 + block_to_free = block;
60 + block = block->next_block;
61 + free(block_to_free);
62 + }
63 +
64 + free(mem_pool);
65 +}
66 +
67 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
68 {
69 struct mp_block *p = NULL;
@@ -33,12 +78,10 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
78 p = mem_pool->mp_block;
79
80 if (!p) {
36 - if (len >= (mem_pool->block_alloc / 2)) {
37 - mem_pool->pool_alloc += len;
38 - return xmalloc(len);
39 - }
81 + if (len >= (mem_pool->block_alloc / 2))
82 + return mem_pool_alloc_block(mem_pool, len, mem_pool->mp_block);
83
41 - p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
84 + p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc, NULL);
85 }
86
87 r = p->next_free;
mem-pool.h
+10
@@ -21,6 +21,16 @@ struct mem_pool {
21 size_t pool_alloc;
22 };
23
24 +/*
25 + * Initialize mem_pool with specified initial size.
26 + */
27 +void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
28 +
29 +/*
30 + * Discard a memory pool and free all the memory it is responsible for.
31 + */
32 +void mem_pool_discard(struct mem_pool *mem_pool);
33 +
34 /*
35 * Alloc memory from the mem_pool.
36 */