Linux Slub分配器(6)-slab的分配与释放

2012-07-18

Linux Slub分配器(六)--slab的分配与释放创建新的slab主要有两个工作，一个是从伙伴系统分配2^order个连续

Linux Slub分配器(六)--slab的分配与释放

创建新的slab主要有两个工作，一个是从伙伴系统分配2^order个连续页框给该slab,然后就是划分slab中的对象。

函数new_slab()用来创建一个新的slab.

static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node){struct page *page;void *start;void *last;void *p;BUG_ON(flags & GFP_SLAB_BUG_MASK);/*为待创建的slab分配页框*/page = allocate_slab(s,flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node);if (!page)goto out;    /*增加slab计数*/inc_slabs_node(s, page_to_nid(page), page->objects);page->slab = s;//设置页描述符的slab指针page->flags |= 1 << PG_slab;//为页框增加一个slab属性if (s->flags & (SLAB_DEBUG_FREE | SLAB_RED_ZONE | SLAB_POISON |SLAB_STORE_USER | SLAB_TRACE))__SetPageSlubDebug(page);/*获取页框的虚拟地址*/start = page_address(page);if (unlikely(s->flags & SLAB_POISON))memset(start, POISON_INUSE, PAGE_SIZE << compound_order(page));last = start;for_each_object(p, s, start, page->objects) {setup_object(s, page, last);//调用构造函数set_freepointer(s, last, p); //设置空闲指针，即last后面的空闲对象为plast = p;}setup_object(s, page, last);set_freepointer(s, last, NULL);  //最后一个对象的空闲指针设为NULL/*设置page的freelist和inuse*/page->freelist = start;page->inuse = 0;out:return page;}

static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node){struct page *page;struct kmem_cache_order_objects oo = s->oo;gfp_t alloc_gfp;flags |= s->allocflags;/* * Let the initial higher-order allocation fail under memory pressure * so we fall-back to the minimum order allocation. */ /*确定gfp标识*/alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;/*分配页框*/page = alloc_slab_page(alloc_gfp, node, oo);/*如果分配失败，则按min的标准进行分配*/if (unlikely(!page)) {oo = s->min;/* * Allocation may have failed due to fragmentation. * Try a lower order alloc if possible */page = alloc_slab_page(flags, node, oo);if (!page)return NULL;stat(get_cpu_slab(s, raw_smp_processor_id()), ORDER_FALLBACK);}if (kmemcheck_enabled&& !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {int pages = 1 << oo_order(oo);kmemcheck_alloc_shadow(page, oo_order(oo), flags, node);/* * Objects from caches that have a constructor don't get * cleared when they're allocated, so we need to do it here. */if (s->ctor)kmemcheck_mark_uninitialized_pages(page, pages);elsekmemcheck_mark_unallocated_pages(page, pages);}page->objects = oo_objects(oo);//从oo中提取出slab中的对象数放到保存到page的objects中mod_zone_page_state(page_zone(page),(s->flags & SLAB_RECLAIM_ACCOUNT) ?NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,1 << oo_order(oo));return page;}

函数alloc_slab_page()便是Slub分配器与伙伴系统的接口！

static inline struct page *alloc_slab_page(gfp_t flags, int node,struct kmem_cache_order_objects oo){int order = oo_order(oo);//从oo中提取出分配阶数flags |= __GFP_NOTRACK;/*从伙伴系统中分配2^order个连续页框*/if (node == -1)return alloc_pages(flags, order);elsereturn alloc_pages_node(node, flags, order);}

获得了所需的页框后，接下来就是在这些页框中划分对象，将他们全部组织起来

for_each_object(p, s, start, page->objects) {setup_object(s, page, last);//调用构造函数set_freepointer(s, last, p); //设置空闲指针，即last后面的空闲对象为plast = p;}

#define for_each_object(__p, __s, __addr, __objects) \for (__p = (__addr); __p < (__addr) + (__objects) * (__s)->size;\__p += (__s)->size)

static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp){/*注意kmem_cache中的offset是以字节为单位的*/*(void **)(object + s->offset) = fp;}

初始化后的对象如下图所示

Linux Slub分配器(6)-slab的分配与释放

销毁slab通过函数discard_slab()来完成

static void discard_slab(struct kmem_cache *s, struct page *page){/*减少节点的slab计数和对象计数*/dec_slabs_node(s, page_to_nid(page), page->objects);free_slab(s, page);//释放slab}

static void free_slab(struct kmem_cache *s, struct page *page){if (unlikely(s->flags & SLAB_DESTROY_BY_RCU)) {/* * RCU free overloads the RCU head over the LRU */struct rcu_head *head = (void *)&page->lru;call_rcu(head, rcu_free_slab);//通过RCU方式来释放} else__free_slab(s, page);//将slab所占页框释放回伙伴系统}

1楼zi77642475昨天 18:26: 沙发！

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Linux Slub分配器(6)-slab的分配与释放