Linux内存管理之slab机制（初始化）
来源：岁月联盟
时间：2012-01-10
start_kernel()->mm_init()->kmem_cache_init()
执行流程：
1，初始化静态initkmem_list3三链；
2，初始化cache_cache的nodelists字段为1中的三链；
3，根据内存情况初始化每个slab占用的页面数变量slab_break_gfp_order；
4，将cache_cache加入cache_chain链表中，初始化cache_cache；
5，创建kmalloc所用的general cache：
1）cache的名称和大小存放在两个数据结构对应的数组中，对应大小的cache可以从size数组中找到；
2）先创建INDEX_AC和INDEX_L3下标的cache；
3）循环创建size数组中各个大小的cache；
6，替换静态本地cache全局变量：
1) 替换cache_cache中的arry_cache,本来指向静态变量initarray_cache.cache；
2) 替换malloc_sizes[INDEX_AC].cs_cachep的local cache，原本指向静态变量initarray_generic.cache；
7，替换静态三链
1）替换cache_cache三链，原本指向静态变量initkmem_list3；
2）替换malloc_sizes[INDEX_AC].cs_cachep三链，原本指向静态变量initkmem_list3；
8，更新初始化进度
www.2cto.com
/*
* 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，无法通过kmalloc分配初始化过程中必要的一些对象
，只能使用静态的全局变量
，待slab初始化后期，再使用kmalloc动态分配的对象替换全局变量*/
/* 如前所述，先借用全局变量initkmem_list3表示的slab三链
，每个内存节点对应一组slab三链。initkmem_list3是个slab三链数组，对于每个内存节点，包含三组
：struct kmem_cache的slab三链、struct arraycache_init的slab 三链、struct kmem_list3的slab三链
。这里循环初始化所有内存节点的所有slab三链*/
if (num_possible_nodes() == 1)
use_alien_caches = 0;
/*初始化所有node的所有slab中的三个链表*/
for (i = 0; i < NUM_INIT_LISTS; i++) {
kmem_list3_init(&initkmem_list3[i]);
/* 全局变量cache_cache指向的slab cache包含所有struct kmem_cache对象，不包含cache_cache本身
。这里初始化所有内存节点的struct kmem_cache的slab三链为空。*/
if (i < MAX_NUMNODES)
cache_cache.nodelists[i] = NULL;
}
/* 设置struct kmem_cache的slab三链指向initkmem_list3中的一组slab三链，
CACHE_CACHE为cache在内核cache链表中的索引，
struct kmem_cache对应的cache是内核中创建的第一个cache
，故CACHE_CACHE为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.
*/
/* 全局变量slab_break_gfp_order为每个slab最多占用几个页面
，用来抑制碎片，比如大小为3360的对象
，如果其slab只占一个页面，碎片为736
，slab占用两个页面，则碎片大小也翻倍
。只有当对象很大
，以至于slab中连一个对象都放不下时
，才可以超过这个值
。有两个可能的取值
：当可用内存大于32MB时
，BREAK_GFP_ORDER_HI为1
，即每个slab最多占用2个页面
，只有当对象大小大于8192时
，才可以突破slab_break_gfp_order的限制
。小于等于32MB时BREAK_GFP_ORDER_LO为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，创建struct kmem_cache所在的cache，由全局变量cache_cache指向
，这里只是初始化数据结构
，并未真正创建这些对象，要待分配时才创建。*/
/* 全局变量cache_chain是内核slab cache链表的表头*/
INIT_LIST_HEAD(&cache_chain);
/* 将cache_cache加入到slab cache链表*/
list_add(&cache_cache.next, &cache_chain);
/* 设置cache着色基本单位为cache line的大小：32字节*/
cache_cache.colour_off = cache_line_size();
/* 初始化cache_cache的local cache，同样这里也不能使用kmalloc
，需要使用静态分配的全局变量initarray_cache */
cache_cache.array[smp_processor_id()] = &initarray_cache.cache;
/* 初始化slab链表,用全局变量*/
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中对象的大小，这里是计算struct kmem_cache的大小
，nodelists是最后一个成员
，nr_node_ids保存内存节点个数，UMA为1
，所以nodelists偏移加上1个struct kmem_list3 的大小即为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
/* 将对象大小与cache line大小对齐*/
cache_cache.buffer_size = ALIGN(cache_cache.buffer_size,
cache_line_size());
/* 计算对象大小的倒数，用于计算对象在slab中的索引*/
cache_cache.reciprocal_buffer_size =
reciprocal_value(cache_cache.buffer_size);
for (order = 0; order < MAX_ORDER; order++) {
/* 计算cache_cache中的对象数目*/
cache_estimate(order, cache_cache.buffer_size,
cache_line_size(), 0, &left_over, &cache_cache.num);
/* num不为0意味着创建struct kmem_cache对象成功，退出*/
if (cache_cache.num)
break;
}
BUG_ON(!cache_cache.num);
/* gfporder表示本slab包含2^gfporder个页面*/
cache_cache.gfporder = order;
/* 着色区的大小，以colour_off为单位*/
cache_cache.colour = left_over / cache_cache.colour_off;
/* slab管理对象的大小*/
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，创建kmalloc所用的general cache
，kmalloc所用的对象按大小分级
，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.
*/
/* 首先创建struct array_cache和struct kmem_list3所用的general cache
，它们是后续初始化动作的基础*/
/* INDEX_AC是计算local cache所用的struct arraycache_init对象在kmalloc size中的索引
，即属于哪一级别大小的general cache
，创建此大小级别的cache为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对应的kmalloc size索引不同
，即大小属于不同的级别
，则创建struct kmem_list3所用的cache，否则共用一个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);
}
/* 创建完上述两个general cache后，slab early init阶段结束，在此之前
，不允许创建外置式slab */
slab_early_init = 0;
/* 循环创建kmalloc各级别的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.
*/
/* 某级别的kmalloc cache还未创建，创建之，struct kmem_list3和
struct arraycache_init对应的cache已经创建过了*/
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已经创建完毕，可以拿来使用了*/
/* 4) Replace the bootstrap head arrays */
/* 第四步，用kmalloc对象替换静态分配的全局变量
。到目前为止一共使用了两个全局local cache
，一个是cache_cache的local cache指向initarray_cache.cache
，另一个是malloc_sizes[INDEX_AC].cs_cachep的local cache指向initarray_generic.cache
，参见setup_cpu_cache函数。这里替换它们。*/
{
struct array_cache *ptr;
/* 申请cache_cache所用local cache的空间*/
ptr = kmalloc(sizeof(struct arraycache_init), GFP_NOWAIT);
BUG_ON(cpu_cache_get(&cache_cache) != &initarray_cache.cache);
/* 复制原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;
/* 申请malloc_sizes[INDEX_AC].cs_cachep所用local cache的空间*/
ptr = kmalloc(sizeof(struct arraycache_init), GFP_NOWAIT);
BUG_ON(cpu_cache_get(malloc_sizes[INDEX_AC].cs_cachep)
!= &initarray_generic.cache);
/* 复制原local cache到新分配的位置，注意此时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，与第四步类似，用kmalloc的空间替换静态分配的slab三链*/
{
int nid;
/* UMA只有一个节点*/
for_each_online_node(nid) {
/* 复制struct kmem_cache的slab三链*/
init_list(&cache_cache, &initkmem_list3[CACHE_CACHE + nid], nid);
/* 复制struct arraycache_init的slab三链*/
init_list(malloc_sizes[INDEX_AC].cs_cachep,
&initkmem_list3[SIZE_AC + nid], nid);
/* 复制struct kmem_list3的slab三链*/
if (INDEX_AC != INDEX_L3) {
init_list(malloc_sizes[INDEX_L3].cs_cachep,
&initkmem_list3[SIZE_L3 + nid], nid);
}
}
}
/* 更新slab系统初始化进度*/
g_cpucache_up = EARLY;
}
辅助操作
1，slab三链初始化
www.2cto.com
static void kmem_list3_init(struct kmem_list3 *parent)
{
INIT_LIST_HEAD(&parent->slabs_full);
INIT_LIST_HEAD(&parent->slabs_partial);
INIT_LIST_HEAD(&parent->slabs_free);
parent->shared = NULL;
parent->alien = NULL;
parent->colour_next = 0;
spin_lock_init(&parent->list_lock);
parent->free_objects = 0;
parent->free_touched = 0;
}
2，slab三链静态数据初始化
www.2cto.com
/*设置cache的slab三链指向静态分配的全局变量*/
static void __init set_up_list3s(struct kmem_cache *cachep, int index)
{
int node;
/* UMA只有一个节点*/
for_each_online_node(node) {
/* 全局变量initkmem_list3是初始化阶段使用的slab三链*/
cachep->nodelists[node] = &initkmem_list3[index + node];
/* 设置回收时间*/
cachep->nodelists[node]->next_reap = jiffies +
REAPTIMEOUT_LIST3 +
((unsigned long)cachep) % REAPTIMEOUT_LIST3;
}
}
3，计算每个slab中对象的数目
www.2cto.com
/*
* Calculate the number of objects and left-over bytes for a given buffer size.
*/
/*计算每个slab中对象的数目。*/
/*
1) gfporder：slab由2gfporder个页面组成。
2) buffer_size：对象的大小。
3) align：对象的对齐方式。
4) flags：内置式slab还是外置式slab。
5) left_over：slab中浪费空间的大小。
6) num：slab中的对象数目。
*/
static void cache_estimate(unsigned long gfporder, size_t buffer_size,
size_t align, int flags, size_t *left_over,
unsigned int *num)
{
int nr_objs;
size_t mgmt_size;
/* slab大小为1<<order个页面*/
size_t slab_size = PAGE_SIZE << gfporder;
/*
* The slab management structure can be either off the slab or
* on it. For the latter case, the memory allocated for a
* slab is used for:
*
* - The struct slab
* - One kmem_bufctl_t for each object
* - Padding to respect alignment of @align
* - @buffer_size bytes for each object
*
* If the slab management structure is off the slab, then the
* alignment will already be calculated into the size. Because
* the slabs are all pages aligned, the objects will be at the
* correct alignment when allocated.
*/
if (flags & CFLGS_OFF_SLAB) {
/* 外置式slab */
mgmt_size = 0;
/* slab页面不含slab管理对象，全部用来存储slab对象*/
nr_objs = slab_size / buffer_size;
/* 对象数不能超过上限*/
if (nr_objs > SLAB_LIMIT)
nr_objs = SLAB_LIMIT;
} else {
/*
* Ignore padding for the initial guess. The padding
* is at most @align-1 bytes, and @buffer_size is at
* least @align. In the worst case, this result will
* be one greater than the number of objects that fit
* into the memory allocation when taking the padding
* into account.
*//* 内置式slab，slab管理对象与slab对象在一起
，此时slab页面中包含：一个struct slab对象，一个kmem_bufctl_t数组，slab对象。
kmem_bufctl_t数组大小与slab对象数目相同*/
nr_objs = (slab_size - sizeof(struct slab)) /
(buffer_size + sizeof(kmem_bufctl_t));
/*
* This calculated number will be either the right
* amount, or one greater than what we want.
*//* 计算cache line对齐后的大小，如果超出了slab总的大小，则对象数减一*/
if (slab_mgmt_size(nr_objs, align) + nr_objs*buffer_size
> slab_size)
nr_objs--;
if (nr_objs > SLAB_LIMIT)
nr_objs = SLAB_LIMIT;
/* 计算cache line对齐后slab管理对象的大小*/
mgmt_size = slab_mgmt_size(nr_objs, align);
}
*num = nr_objs;/* 保存slab对象数目*/
/* 计算浪费空间的大小*/
*left_over = slab_size - nr_objs*buffer_size - mgmt_size;
}
辅助数据结构与变量
Linux内核中将所有的通用cache以不同的大小存放在数组中，以方便查找。其中malloc_sizes[]数组为cache_sizes类型的数组，存放各个cache的大小；cache_names[]数组为cache_names结构类型数组，存放各个cache大小的名称；malloc_sizes[]数组和cache_names[]数组下标对应，也就是说cache_names[i]名称的cache对应的大小为malloc_sizes[i]。
www.2cto.com
/* Size description struct for general caches. */
struct cache_sizes {
size_t cs_size;
struct kmem_cache *cs_cachep;
#ifdef CONFIG_ZONE_DMA
struct kmem_cache *cs_dmacachep;
#endif
};
/*
* These are the default caches for kmalloc. Custom caches can have other sizes.
*/
struct cache_sizes malloc_sizes[] = {
#define CACHE(x) { .cs_size = (x) },
#include <linux/kmalloc_sizes.h>
CACHE(ULONG_MAX)
#undef CACHE
};
www.2cto.com
/* Must match cache_sizes above. Out of line to keep cache footprint low. */
struct cache_names {
char *name;
char *name_dma;
};
static struct cache_names __initdata cache_names[] = {
#define CACHE(x) { .name = "size-" #x, .name_dma = "size-" #x "(DMA)" },
#include <linux/kmalloc_sizes.h>
{NULL,}
#undef CACHE
};
二、内核启动末期初始化
1，根据对象大小计算local cache中对象数目上限；
2，借助数据结构ccupdate_struct操作cpu本地cache。为每个在线cpu分配cpu本地cache；
3，用新分配的cpu本地cache替换原有的cache；
4，更新slab三链以及cpu本地共享cache。
第二阶段代码分析
Start_kernel()->kmem_cache_init_late()
www.2cto.com
/*Slab系统初始化分两个部分，先初始化一些基本的，待系统初始化工作进行的差不多时，再配置一些特殊功能。*/
void __init kmem_cache_init_late(void)
{
struct kmem_cache *cachep;
/* 初始化阶段local cache的大小是固定的，要根据对象大小重新计算*/
/* 6) resize the head arrays to their final sizes */
mutex_lock(&cache_chain_mutex);
list_for_each_entry(cachep, &cache_chain, next)
if (enable_cpucache(cachep, GFP_NOWAIT))
BUG();
mutex_unlock(&cache_chain_mutex);
/* Done! */
/* 大功告成，general cache终于全部建立起来了*/
g_cpucache_up = FULL;
/* Annotate slab for lockdep -- annotate the malloc caches */
init_lock_keys();
/*
* Register a cpu startup notifier callback that initializes
* cpu_cache_get for all new cpus
*/
/* 注册cpu up回调函数，cpu up时配置local cache */
register_cpu_notifier(&cpucache_notifier);
/*
* The reap timers are started later, with a module init call: That part
* of the kernel is not yet operational.
*/
}
www.2cto.com
/* Called with cache_chain_mutex held always */
/*local cache 初始化*/
static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp)
{
int err;
int limit, shared;
/*
* The head array serves three purposes:
* - create a LIFO ordering, i.e. return objects that are cache-warm
* - reduce the number of spinlock operations.
* - reduce the number of linked list operations on the slab and
* bufctl chains: array operations are cheaper.
* The numbers are guessed, we should auto-tune as described by
* Bonwick.
*/ /* 根据对象大小计算local cache中对象数目上限*/
if (cachep->buffer_size > 131072)
limit = 1;
else if (cachep->buffer_size > PAGE_SIZE)
limit = 8;
else if (cachep->buffer_size > 1024)
limit = 24;
else if (cachep->buffer_size > 256)
limit = 54;
else
limit = 120;
/*
* CPU bound tasks (e.g. network routing) can exhibit cpu bound
* allocation behaviour: Most allocs on one cpu, most free operations
* on another cpu. For these cases, an efficient object passing between
* cpus is necessary. This is provided by a shared array. The array
* replaces Bonwick's magazine layer.
* On uniprocessor, it's functionally equivalent (but less efficient)
* to a larger limit. Thus disabled by default.
*/
shared = 0;
/* 多核系统，设置shared local cache中对象数目*/
if (cachep->buffer_size <= PAGE_SIZE && num_possible_cpus() > 1)
shared = 8;
#if DEBUG
/*
* With debugging enabled, large batchcount lead to excessively long
* periods with disabled local interrupts. Limit the batchcount
*/
if (limit > 32)
limit = 32;
#endif
/* 配置local cache */
err = do_tune_cpucache(cachep, limit, (limit + 1) / 2, shared, gfp);
if (err)
printk(KERN_ERR "enable_cpucache failed for %s, error %d./n",
cachep->name, -err);
return err;
}
www.2cto.com
/* Always called with the cache_chain_mutex held */
/*配置local cache、shared local cache和slab三链*/
static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
int batchcount, int shared, gfp_t gfp)
{
struct ccupdate_struct *new;
int i;
new = kzalloc(sizeof(*new), gfp);
if (!new)
return -ENOMEM;
/* 为每个cpu分配新的struct array_cache对象*/
for_each_online_cpu(i) {
new->new[i] = alloc_arraycache(cpu_to_node(i), limit,
batchcount, gfp);
if (!new->new[i]) {
for (i--; i >= 0; i--)
kfree(new->new[i]);
kfree(new);
return -ENOMEM;
}
}
new->cachep = cachep;
/* 用新的struct array_cache对象替换旧的struct array_cache对象
，在支持cpu热插拔的系统上，离线cpu可能没有释放local cache
，使用的仍是旧local cache，参见__kmem_cache_destroy函数
。虽然cpu up时要重新配置local cache，也无济于事。考虑下面的情景
：共有Cpu A和Cpu B，Cpu B down后，destroy Cache X，由于此时Cpu B是down状态
，所以Cache X中Cpu B的local cache未释放，过一段时间Cpu B又up了
，更新cache_chain 链中所有cache的local cache，但此时Cache X对象已经释放回
cache_cache中了，其Cpu B local cache并未被更新。又过了一段时间
，系统需要创建新的cache，将Cache X对象分配出去，其Cpu B仍然是旧的
local cache，需要进行更新。
*/
on_each_cpu(do_ccupdate_local, (void *)new, 1);
check_irq_on();
cachep->batchcount = batchcount;
cachep->limit = limit;
cachep->shared = shared;
/* 释放旧的local cache */
for_each_online_cpu(i) {
struct array_cache *ccold = new->new[i];
if (!ccold)
continue;
spin_lock_irq(&cachep->nodelists[cpu_to_node(i)]->list_lock);
/* 释放旧local cache中的对象*/
free_block(cachep, ccold->entry, ccold->avail, cpu_to_node(i));
spin_unlock_irq(&cachep->nodelists[cpu_to_node(i)]->list_lock);
/* 释放旧的struct array_cache对象*/
kfree(ccold);
}
kfree(new);
/* 初始化shared local cache 和slab三链*/
return alloc_kmemlist(cachep, gfp);
}
更新本地cache
www.2cto.com
/*更新每个cpu的struct array_cache对象*/
static void do_ccupdate_local(void *info)
{
struct ccupdate_struct *new = info;
struct array_cache *old;
check_irq_off();
old = cpu_cache_get(new->cachep);
/* 指向新的struct array_cache对象*/
new->cachep->array[smp_processor_id()] = new->new[smp_processor_id()];
/* 保存旧的struct array_cache对象*/
new->new[smp_processor_id()] = old;
}
www.2cto.com
/*初始化shared local cache和slab三链，初始化完成后，slab三链中没有任何slab*/
static int alloc_kmemlist(struct kmem_cache *cachep, gfp_t gfp)
{
int node;
struct kmem_list3 *l3;
struct array_cache *new_shared;
struct array_cache **new_alien = NULL;
for_each_online_node(node) {
/* NUMA相关*/
if (use_alien_caches) {
new_alien = alloc_alien_cache(node, cachep->limit, gfp);
if (!new_alien)
goto fail;
}
new_shared = NULL;
if (cachep->shared) {
/* 分配shared local cache */
new_shared = alloc_arraycache(node,
cachep->shared*cachep->batchcount,
0xbaadf00d, gfp);
if (!new_shared) {
free_alien_cache(new_alien);
goto fail;
}
}
/* 获得旧的slab三链*/
l3 = cachep->nodelists[node];
if (l3) {
/* 就slab三链指针不为空，需要先释放旧的资源*/
struct array_cache *shared = l3->shared;
spin_lock_irq(&l3->list_lock);
/* 释放旧的shared local cache中的对象*/
if (shared)
free_block(cachep, shared->entry,
shared->avail, node);
/* 指向新的shared local cache */
l3->shared = new_shared;
if (!l3->alien) {
l3->alien = new_alien;
new_alien = NULL;
}/* 计算cache中空闲对象的上限*/
l3->free_limit = (1 + nr_cpus_node(node)) *
cachep->batchcount + cachep->num;
spin_unlock_irq(&l3->list_lock);
/* 释放旧shared local cache的struct array_cache对象*/
kfree(shared);
free_alien_cache(new_alien);
continue;/*访问下一个节点*/
}
/* 如果没有旧的l3，分配新的slab三链*/
l3 = kmalloc_node(sizeof(struct kmem_list3), gfp, node);
if (!l3) {
free_alien_cache(new_alien);
kfree(new_shared);
goto fail;
}
/* 初始化slab三链*/
kmem_list3_init(l3);
l3->next_reap = jiffies + REAPTIMEOUT_LIST3 +
((unsigned long)cachep) % REAPTIMEOUT_LIST3;
l3->shared = new_shared;
l3->alien = new_alien;
l3->free_limit = (1 + nr_cpus_node(node)) *
cachep->batchcount + cachep->num;
cachep->nodelists[node] = l3;
}
return 0;
fail:
if (!cachep->next.next) {
/* Cache is not active yet. Roll back what we did */
node--;
while (node >= 0) {
if (cachep->nodelists[node]) {
l3 = cachep->nodelists[node];
kfree(l3->shared);
free_alien_cache(l3->alien);
kfree(l3);
cachep->nodelists[node] = NULL;
}
node--;
}
}
return -ENOMEM;
}
看一个辅助函数
/*分配struct array_cache对象。*/
static struct array_cache *alloc_arraycache(int node, int entries,
int batchcount, gfp_t gfp)
{
/* struct array_cache后面紧接着的是entry数组，合在一起申请内存*/
int memsize = sizeof(void *) * entries + sizeof(struct array_cache);
struct array_cache *nc = NULL;
/* 分配一个local cache对象，kmalloc从general cache中分配*/
nc = kmalloc_node(memsize, gfp, node);
/*
* The array_cache structures contain pointers to free object.
* However, when such objects are allocated or transfered to another
* cache the pointers are not cleared and they could be counted as
* valid references during a kmemleak scan. Therefore, kmemleak must
* not scan such objects.
*/
kmemleak_no_scan(nc);
/* 初始化local cache */
if (nc) {
nc->avail = 0;
nc->limit = entries;
nc->batchcount = batchcount;
nc->touched = 0;
spin_lock_init(&nc->lock);
}
return nc;
}
源代码中涉及了slab的分配、释放等操作在后面分析中陆续总结。slab相关数据结构、工作机制以及整体框架在分析完了slab的创建、释放工作后再做总结，这样可能会对slab机制有更好的了解。当然，从代码中看运行机制会更有说服了，也是一种习惯
摘自 bullbat的专栏
