Linux Slab分配器(6)-创建slab和销毁slab

2012-06-20

Linux Slab分配器(六)--创建slab和销毁slab在满足以下两个条件时，slab分配器将为高速缓存创建新的slab1.请

Linux Slab分配器(六)--创建slab和销毁slab

在满足以下两个条件时，slab分配器将为高速缓存创建新的slab

1.请求分配对象，但本地高速缓存没有空闲对象可以分配，需要填充

2.kmem_list3维护的链表中没有slab或者所有的slab都处于FULL链表中

这时，调用cache_grow()创建slab增大缓存容量

下图给出了cache_grow()的代码流程

Linux Slab分配器(6)-创建slab和销毁slab

static int cache_grow(struct kmem_cache *cachep,gfp_t flags, int nodeid, void *objp){struct slab *slabp;size_t offset;gfp_t local_flags;struct kmem_list3 *l3;/* * Be lazy and only check for valid flags here,  keeping it out of the * critical path in kmem_cache_alloc(). */BUG_ON(flags & GFP_SLAB_BUG_MASK);local_flags = flags & (GFP_CONSTRAINT_MASK|GFP_RECLAIM_MASK);/* Take the l3 list lock to change the colour_next on this node */check_irq_off();l3 = cachep->nodelists[nodeid];spin_lock(&l3->list_lock);/* Get colour for the slab, and cal the next value. *//*确定待创建的slab的颜色编号*/offset = l3->colour_next;/*更新下一个slab的颜色编号*/l3->colour_next++;/*颜色编号必须小于颜色数*/if (l3->colour_next >= cachep->colour)l3->colour_next = 0;spin_unlock(&l3->list_lock);/*确定待创建的slab的颜色*/offset *= cachep->colour_off;if (local_flags & __GFP_WAIT)local_irq_enable();/* * The test for missing atomic flag is performed here, rather than * the more obvious place, simply to reduce the critical path length * in kmem_cache_alloc(). If a caller is seriously mis-behaving they * will eventually be caught here (where it matters). */kmem_flagcheck(cachep, flags);/* * Get mem for the objs.  Attempt to allocate a physical page from * 'nodeid'. */if (!objp)/*从伙伴系统分配页框，这是slab分配器与伙伴系统的接口*/objp = kmem_getpages(cachep, local_flags, nodeid);if (!objp)goto failed;/* Get slab management. *//*分配slab管理区*/slabp = alloc_slabmgmt(cachep, objp, offset,local_flags & ~GFP_CONSTRAINT_MASK, nodeid);if (!slabp)goto opps1;/*建立页面到slab和cache的映射，以便于根据obj迅速定位slab描述符和cache描述符*/slab_map_pages(cachep, slabp, objp);/*初始化对象*/cache_init_objs(cachep, slabp);if (local_flags & __GFP_WAIT)local_irq_disable();check_irq_off();spin_lock(&l3->list_lock);/* Make slab active. *//*将新创建的slab添加到free链表*/list_add_tail(&slabp->list, &(l3->slabs_free));STATS_INC_GROWN(cachep);l3->free_objects += cachep->num;spin_unlock(&l3->list_lock);return 1;opps1:kmem_freepages(cachep, objp);failed:if (local_flags & __GFP_WAIT)local_irq_disable();return 0;}

辅助函数：

为slab分配页框

static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid){struct page *page;int nr_pages;int i;#ifndef CONFIG_MMU/* * Nommu uses slab's for process anonymous memory allocations, and thus * requires __GFP_COMP to properly refcount higher order allocations */flags |= __GFP_COMP;#endifflags |= cachep->gfpflags;if (cachep->flags & SLAB_RECLAIM_ACCOUNT)flags |= __GFP_RECLAIMABLE;/*从特定的节点分配2^gfporder个连续页*/page = alloc_pages_exact_node(nodeid, flags | __GFP_NOTRACK, cachep->gfporder);if (!page)return NULL;nr_pages = (1 << cachep->gfporder);if (cachep->flags & SLAB_RECLAIM_ACCOUNT)add_zone_page_state(page_zone(page),NR_SLAB_RECLAIMABLE, nr_pages);elseadd_zone_page_state(page_zone(page),NR_SLAB_UNRECLAIMABLE, nr_pages);for (i = 0; i < nr_pages; i++)__SetPageSlab(page + i);if (kmemcheck_enabled && !(cachep->flags & SLAB_NOTRACK)) {kmemcheck_alloc_shadow(page, cachep->gfporder, flags, nodeid);if (cachep->ctor)kmemcheck_mark_uninitialized_pages(page, nr_pages);elsekmemcheck_mark_unallocated_pages(page, nr_pages);}/*返回首页的虚拟地址*/return page_address(page);}

为slab管理区分配空间:

static struct slab *alloc_slabmgmt(struct kmem_cache *cachep, void *objp,   int colour_off, gfp_t local_flags,   int nodeid){struct slab *slabp;/*如果slab管理区位于slab外，则在指定的slabp_cache中分配空间*/if (OFF_SLAB(cachep)) {/* Slab management obj is off-slab. */slabp = kmem_cache_alloc_node(cachep->slabp_cache,      local_flags, nodeid);/* * If the first object in the slab is leaked (it's allocated * but no one has a reference to it), we want to make sure * kmemleak does not treat the ->s_mem pointer as a reference * to the object. Otherwise we will not report the leak. */kmemleak_scan_area(slabp, offsetof(struct slab, list),   sizeof(struct list_head), local_flags);if (!slabp)return NULL;} else {/*slab管理区处于slab中*//*slab管理区从slab首部偏移颜色值的地方开始*/slabp = objp + colour_off;colour_off += cachep->slab_size;}slabp->inuse = 0;/*对象全为空闲*/slabp->colouroff = colour_off;   /*刷新第一个对象的偏移*/slabp->s_mem = objp + colour_off;/*确定第一个对象的位置*/slabp->nodeid = nodeid;/*标识节点*/slabp->free = 0; /*下一个空闲对象位于s_mem起始处*/return slabp;}

利用页描述结构的lru域建立页框到slab描述符和cache描述符的映射，实际就是使lru.next指向cache描述符，lru.prev指向slab描述符

static void slab_map_pages(struct kmem_cache *cache, struct slab *slab,   void *addr){int nr_pages;struct page *page;page = virt_to_page(addr);nr_pages = 1;if (likely(!PageCompound(page)))nr_pages <<= cache->gfporder;/*分配给slab的页框数*/do {page_set_cache(page, cache);/*建立到cache的映射*/page_set_slab(page, slab);  /*建立到slab的映射*/page++;} while (--nr_pages);}

static inline void page_set_cache(struct page *page, struct kmem_cache *cache){page->lru.next = (struct list_head *)cache;}

static inline void page_set_slab(struct page *page, struct slab *slab){page->lru.prev = (struct list_head *)slab;}

初始化对象

static void cache_init_objs(struct kmem_cache *cachep,    struct slab *slabp){int i;for (i = 0; i < cachep->num; i++) {/*得到第i个对象*/void *objp = index_to_obj(cachep, slabp, i);#if DEBUG /*Debug相关操作*//* need to poison the objs? */if (cachep->flags & SLAB_POISON)poison_obj(cachep, objp, POISON_FREE);if (cachep->flags & SLAB_STORE_USER)*dbg_userword(cachep, objp) = NULL;if (cachep->flags & SLAB_RED_ZONE) {*dbg_redzone1(cachep, objp) = RED_INACTIVE;*dbg_redzone2(cachep, objp) = RED_INACTIVE;}/* * Constructors are not allowed to allocate memory from the same * cache which they are a constructor for.  Otherwise, deadlock. * They must also be threaded. */if (cachep->ctor && !(cachep->flags & SLAB_POISON))cachep->ctor(objp + obj_offset(cachep));if (cachep->flags & SLAB_RED_ZONE) {if (*dbg_redzone2(cachep, objp) != RED_INACTIVE)slab_error(cachep, "constructor overwrote the"   " end of an object");if (*dbg_redzone1(cachep, objp) != RED_INACTIVE)slab_error(cachep, "constructor overwrote the"   " start of an object");}if ((cachep->buffer_size % PAGE_SIZE) == 0 &&    OFF_SLAB(cachep) && cachep->flags & SLAB_POISON)kernel_map_pages(virt_to_page(objp), cachep->buffer_size / PAGE_SIZE, 0);#elseif (cachep->ctor)/*根据构造函数初始化对象*/cachep->ctor(objp);#endifslab_bufctl(slabp)[i] = i + 1;/*确定下一个空闲对象为后面相邻的对象*/}slab_bufctl(slabp)[i - 1] = BUFCTL_END;}

销毁slab就是释放slab管理区和对象占用的空间

static void slab_destroy(struct kmem_cache *cachep, struct slab *slabp){   /*用第一个对象的地址减去着色偏移量得到slab的起始地址*/void *addr = slabp->s_mem - slabp->colouroff;slab_destroy_debugcheck(cachep, slabp);/*如果选择了RCU方式来销毁slab,则通过RCU进行销毁，这个表示还不太明白*/if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU)) {struct slab_rcu *slab_rcu;slab_rcu = (struct slab_rcu *)slabp;slab_rcu->cachep = cachep;slab_rcu->addr = addr;call_rcu(&slab_rcu->head, kmem_rcu_free);} else {/*将slab占用的页框释放回伙伴系统*/kmem_freepages(cachep, addr);/*如果slab的管理区位于外部，则需要从对应的缓存中释放管理区对象*/if (OFF_SLAB(cachep))kmem_cache_free(cachep->slabp_cache, slabp);}}

1楼zi77642475昨天 15:46: 各位看官，看博主的博客这么久了，觉得他的水平应该是个什么身份呢？呵呵！沙发依然在哦！

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Linux Slab分配器(6)-创建slab和销毁slab