一、內核啟動早期初始化
start_kernel()->mm_init()->kmem_cache_init()
執行流程:
1,初始化靜態initkmem_list3三鏈;
2,初始化cache_cache的nodelists字段為1中的三鏈;
3,根據內存情況初始化每個slab占用的頁面數變量slab_break_gfp_order;
4,將cache_cache加入cache_chain鏈表中,初始化cache_cache;
5,創建kmalloc所用的general cache:
1)cache的名稱和大小存放在兩個數據結構對應的數組中,對應大小的cache可以從size數組中找到;
2)先創建INDEX_AC和INDEX_L3下標的cache;
3)循環創建size數組中各個大小的cache;
6,替換靜態本地cache全局變量:
1) 替換cache_cache中的arry_cache,本來指向靜態變量initarray_cache.cache;
2) 替換malloc_sizes[INDEX_AC].cs_cachep的local cache,原本指向靜態變量initarray_generic.cache;
7,替換靜態三鏈
1)替換cache_cache三鏈,原本指向靜態變量initkmem_list3;
2)替換malloc_sizes[INDEX_AC].cs_cachep三鏈,原本指向靜態變量initkmem_list3;
8,更新初始化進度
- /*
- * Initialisation. Called after the page allocator have been initialised and
- * before smp_init().
- */
- void __init kmem_cache_init(void)
- {
- size_t left_over;
- struct cache_sizes *sizes;
- struct cache_names *names;
- int i;
- int order;
- int node;
- /* 在slab初始化好之前,無法通過kmalloc分配初始化過程中必要的一些對象
- ,只能使用靜態的全局變量
- ,待slab初始化後期,再使用kmalloc動態分配的對象替換全局變量 */
-
- /* 如前所述,先借用全局變量initkmem_list3表示的slab三鏈
- ,每個內存節點對應一組slab三鏈。initkmem_list3是個slab三鏈數組,對於每個內存節點,包含三組
- :struct kmem_cache的slab三鏈、struct arraycache_init的slab 三鏈、struct kmem_list3的slab三鏈
- 。這裡循環初始化所有內存節點的所有slab三鏈 */
- if (num_possible_nodes() == 1)
- use_alien_caches = 0;
- /*初始化所有node的所有slab中的三個鏈表*/
- for (i = 0; i < NUM_INIT_LISTS; i++) {
- kmem_list3_init(&initkmem_list3[i]);
- /* 全局變量cache_cache指向的slab cache包含所有struct kmem_cache對象,不包含cache_cache本身
- 。這裡初始化所有內存節點的struct kmem_cache的slab三鏈為空。*/
- if (i < MAX_NUMNODES)
- cache_cache.nodelists[i] = NULL;
- }
- /* 設置struct kmem_cache的slab三鏈指向initkmem_list3中的一組slab三鏈,
- CACHE_CACHE為cache在內核cache鏈表中的索引,
- struct kmem_cache對應的cache是內核中創建的第一個cache
- ,故CACHE_CACHE為0 */
- set_up_list3s(&cache_cache, CACHE_CACHE);
-
- /*
- * Fragmentation resistance on low memory - only use bigger
- * page orders on machines with more than 32MB of memory.
- */
- /* 全局變量slab_break_gfp_order為每個slab最多占用幾個頁面
- ,用來抑制碎片,比如大小為3360的對象
- ,如果其slab只占一個頁面,碎片為736
- ,slab占用兩個頁面,則碎片大小也翻倍
- 。只有當對象很大
- ,以至於slab中連一個對象都放不下時
- ,才可以超過這個值
- 。有兩個可能的取值
- :當可用內存大於32MB時
- ,BREAK_GFP_ORDER_HI為1
- ,即每個slab最多占用2個頁面
- ,只有當對象大小大於8192時
- ,才可以突破slab_break_gfp_order的限制
- 。小於等於32MB時BREAK_GFP_ORDER_LO為0。*/
- if (totalram_pages > (32 << 20) >> PAGE_SHIFT)
- slab_break_gfp_order = BREAK_GFP_ORDER_HI;
-
- /* Bootstrap is tricky, because several objects are allocated
- * from caches that do not exist yet:
- * 1) initialize the cache_cache cache: it contains the struct
- * kmem_cache structures of all caches, except cache_cache itself:
- * cache_cache is statically allocated.
- * Initially an __init data area is used for the head array and the
- * kmem_list3 structures, it's replaced with a kmalloc allocated
- * array at the end of the bootstrap.
- * 2) Create the first kmalloc cache.
- * The struct kmem_cache for the new cache is allocated normally.
- * An __init data area is used for the head array.
- * 3) Create the remaining kmalloc caches, with minimally sized
- * head arrays.
- * 4) Replace the __init data head arrays for cache_cache and the first
- * kmalloc cache with kmalloc allocated arrays.
- * 5) Replace the __init data for kmem_list3 for cache_cache and
- * the other cache's with kmalloc allocated memory.
- * 6) Resize the head arrays of the kmalloc caches to their final sizes.
- */
-
- node = numa_node_id();
-
- /* 1) create the cache_cache */
- /* 第一步,創建struct kmem_cache所在的cache,由全局變量cache_cache指向
- ,這裡只是初始化數據結構
- ,並未真正創建這些對象,要待分配時才創建。*/
- /* 全局變量cache_chain是內核slab cache鏈表的表頭 */
- INIT_LIST_HEAD(&cache_chain);
-
- /* 將cache_cache加入到slab cache鏈表 */
- list_add(&cache_cache.next, &cache_chain);
-
- /* 設置cache著色基本單位為cache line的大小:32字節 */
- cache_cache.colour_off = cache_line_size();
- /* 初始化cache_cache的local cache,同樣這裡也不能使用kmalloc
- ,需要使用靜態分配的全局變量initarray_cache */
- cache_cache.array[smp_processor_id()] = &initarray_cache.cache;
- /* 初始化slab鏈表 ,用全局變量*/
- cache_cache.nodelists[node] = &initkmem_list3[CACHE_CACHE + node];
-
- /*
- * struct kmem_cache size depends on nr_node_ids, which
- * can be less than MAX_NUMNODES.
- */
- /* buffer_size保存slab中對象的大小,這裡是計算struct kmem_cache的大小
- , nodelists是最後一個成員
- ,nr_node_ids保存內存節點個數,UMA為1
- ,所以nodelists偏移加上1個struct kmem_list3 的大小即為struct kmem_cache的大小 */
- cache_cache.buffer_size = offsetof(struct kmem_cache, nodelists) +
- nr_node_ids * sizeof(struct kmem_list3 *);
- #if DEBUG
- cache_cache.obj_size = cache_cache.buffer_size;
- #endif
- /* 將對象大小與cache line大小對齊 */
- cache_cache.buffer_size = ALIGN(cache_cache.buffer_size,
- cache_line_size());
- /* 計算對象大小的倒數,用於計算對象在slab中的索引 */
- cache_cache.reciprocal_buffer_size =
- reciprocal_value(cache_cache.buffer_size);
-
- for (order = 0; order < MAX_ORDER; order++) {
- /* 計算cache_cache中的對象數目 */
- cache_estimate(order, cache_cache.buffer_size,
- cache_line_size(), 0, &left_over, &cache_cache.num);
- /* num不為0意味著創建struct kmem_cache對象成功,退出 */
- if (cache_cache.num)
- break;
- }
- BUG_ON(!cache_cache.num);
- /* gfporder表示本slab包含2^gfporder個頁面 */
- cache_cache.gfporder = order;
- /* 著色區的大小,以colour_off為單位 */
- cache_cache.colour = left_over / cache_cache.colour_off;
- /* slab管理對象的大小 */
- cache_cache.slab_size = ALIGN(cache_cache.num * sizeof(kmem_bufctl_t) +
- sizeof(struct slab), cache_line_size());
-
- /* 2+3) create the kmalloc caches */
- /* 第二步,創建kmalloc所用的general cache
- ,kmalloc所用的對象按大小分級
- ,malloc_sizes保存大小,cache_names保存cache名 */
- sizes = malloc_sizes;
- names = cache_names;
-
- /*
- * Initialize the caches that provide memory for the array cache and the
- * kmem_list3 structures first. Without this, further allocations will
- * bug.
- */
- /* 首先創建struct array_cache和struct kmem_list3所用的general cache
- ,它們是後續初始化動作的基礎 */
- /* INDEX_AC是計算local cache所用的struct arraycache_init對象在kmalloc size中的索引
- ,即屬於哪一級別大小的general cache
- ,創建此大小級別的cache為local cache所用 */
- sizes[INDEX_AC].cs_cachep = kmem_cache_create(names[INDEX_AC].name,
- sizes[INDEX_AC].cs_size,
- ARCH_KMALLOC_MINALIGN,
- ARCH_KMALLOC_FLAGS|SLAB_PANIC,
- NULL);
- /* 如果struct kmem_list3和struct arraycache_init對應的kmalloc size索引不同
- ,即大小屬於不同的級別
- ,則創建struct kmem_list3所用的cache,否則共用一個cache */
- if (INDEX_AC != INDEX_L3) {
- sizes[INDEX_L3].cs_cachep =
- kmem_cache_create(names[INDEX_L3].name,
- sizes[INDEX_L3].cs_size,
- ARCH_KMALLOC_MINALIGN,
- ARCH_KMALLOC_FLAGS|SLAB_PANIC,
- NULL);
- }
- /* 創建完上述兩個general cache後,slab early init階段結束,在此之前
- ,不允許創建外置式slab */
- slab_early_init = 0;
-
- /* 循環創建kmalloc各級別的general cache */
- while (sizes->cs_size != ULONG_MAX) {
- /*
- * For performance, all the general caches are L1 aligned.
- * This should be particularly beneficial on SMP boxes, as it
- * eliminates "false sharing".
- * Note for systems short on memory removing the alignment will
- * allow tighter packing of the smaller caches.
- */
- /* 某級別的kmalloc cache還未創建,創建之,struct kmem_list3和
- struct arraycache_init對應的cache已經創建過了 */
- if (!sizes->cs_cachep) {
- sizes->cs_cachep = kmem_cache_create(names->name,
- sizes->cs_size,
- ARCH_KMALLOC_MINALIGN,
- ARCH_KMALLOC_FLAGS|SLAB_PANIC,
- NULL);
- }
- #ifdef CONFIG_ZONE_DMA
- sizes->cs_dmacachep = kmem_cache_create(
- names->name_dma,
- sizes->cs_size,
- ARCH_KMALLOC_MINALIGN,
- ARCH_KMALLOC_FLAGS|SLAB_CACHE_DMA|
- SLAB_PANIC,
- NULL);
- #endif
- sizes++;
- names++;
- }
- /* 至此,kmalloc general cache已經創建完畢,可以拿來使用了 */
- /* 4) Replace the bootstrap head arrays */
- /* 第四步,用kmalloc對象替換靜態分配的全局變量
- 。到目前為止一共使用了兩個全局local cache
- ,一個是cache_cache的local cache指向initarray_cache.cache
- ,另一個是malloc_sizes[INDEX_AC].cs_cachep的local cache指向initarray_generic.cache
- ,參見setup_cpu_cache函數。這裡替換它們。*/
- {
- struct array_cache *ptr;
- /* 申請cache_cache所用local cache的空間 */
- ptr = kmalloc(sizeof(struct arraycache_init), GFP_NOWAIT);
-
- BUG_ON(cpu_cache_get(&cache_cache) != &initarray_cache.cache);
- /* 復制原cache_cache的local cache,即initarray_cache,到新的位置 */
- memcpy(ptr, cpu_cache_get(&cache_cache),
- sizeof(struct arraycache_init));
- /*
- * Do not assume that spinlocks can be initialized via memcpy:
- */
- spin_lock_init(&ptr->lock);
- /* cache_cache的local cache指向新的位置 */
- cache_cache.array[smp_processor_id()] = ptr;
- /* 申請malloc_sizes[INDEX_AC].cs_cachep所用local cache的空間 */
- ptr = kmalloc(sizeof(struct arraycache_init), GFP_NOWAIT);
-
- BUG_ON(cpu_cache_get(malloc_sizes[INDEX_AC].cs_cachep)
- != &initarray_generic.cache);
- /* 復制原local cache到新分配的位置,注意此時local cache的大小是固定的 */
- memcpy(ptr, cpu_cache_get(malloc_sizes[INDEX_AC].cs_cachep),
- sizeof(struct arraycache_init));
- /*
- * Do not assume that spinlocks can be initialized via memcpy:
- */
- spin_lock_init(&ptr->lock);
-
- malloc_sizes[INDEX_AC].cs_cachep->array[smp_processor_id()] =
- ptr;
- }
- /* 5) Replace the bootstrap kmem_list3's */
- /* 第五步,與第四步類似,用kmalloc的空間替換靜態分配的slab三鏈 */
- {
- int nid;
- /* UMA只有一個節點 */
- for_each_online_node(nid) {
- /* 復制struct kmem_cache的slab三鏈 */
- init_list(&cache_cache, &initkmem_list3[CACHE_CACHE + nid], nid);
- /* 復制struct arraycache_init的slab三鏈 */
- init_list(malloc_sizes[INDEX_AC].cs_cachep,
- &initkmem_list3[SIZE_AC + nid], nid);
- /* 復制struct kmem_list3的slab三鏈 */
- if (INDEX_AC != INDEX_L3) {
- init_list(malloc_sizes[INDEX_L3].cs_cachep,
- &initkmem_list3[SIZE_L3 + nid], nid);
- }
- }
- }
- /* 更新slab系統初始化進度 */
- g_cpucache_up = EARLY;
- }