内核代码阅读(10) - 内核缓冲区的管理slab下

static inline void kmem_cache_free_one(kmem_cache_t *cachep, void *objp)
    {
        slab_t* slabp;
        CHECK_PAGE(virt_to_page(objp));
        slabp = GET_PAGE_SLAB(virt_to_page(objp));
        {
                unsigned int objnr = (objp-slabp->s_mem)/cachep->objsize;
                slab_bufctl(slabp)[objnr] = slabp->free;
                slabp->free = objnr;
        }
        STATS_DEC_ACTIVE(cachep);
        if (slabp->inuse-- == cachep->num)
                goto moveslab_partial;
        if (!slabp->inuse)
                goto moveslab_free;
        return;
    moveslab_partial:
        {
                struct list_head *t = cachep->firstnotfull;
                cachep->firstnotfull = &slabp->list;
                if (slabp->list.next == t)
                        return;
                list_del(&slabp->list);
                list_add_tail(&slabp->list, t);
                return;
        }
    moveslab_free:
        {
                struct list_head *t = cachep->firstnotfull->prev;
                list_del(&slabp->list);
                list_add_tail(&slabp->list, &cachep->slabs);
                if (cachep->firstnotfull == &slabp->list)
                        cachep->firstnotfull = t->next;
                return;
        }
    }

1) slabp = GET_PAGE_SLAB(virt_to_page(objp));
   通过要释放的物理地址，可以获取到对应的 struct page结构, 通过page结构的list可以找到objp所属的slab。
2) unsigned int objnr = (objp-slabp->s_mem)/cachep->objsize;
   slab_bufctl(slabp)[objnr] = slabp->free;
   计算objp在slab中的下标。
   更新slab中的空闲链接数组。
3) if (slabp->inuse-- == cachep->num)
           goto moveslab_partial;
   更新inuse计数器。

void * kmalloc (size_t size, int flags)
    {
        cache_sizes_t *csizep = cache_sizes;
        for (; csizep->cs_size; csizep++) {
                if (size > csizep->cs_size)
                        continue;
                return __kmem_cache_alloc(flags & GFP_DMA ?
                         csizep->cs_dmacachep : csizep->cs_cachep, flags);
        }
        return NULL;
    }

1) cache_sizes 是一个cache_sizes_t的结构数组。
   typedef struct cache_sizes {
       size_t                 cs_size;
       kmem_cache_t        *cs_cachep;
       kmem_cache_t        *cs_dmacachep;
   } cache_sizes_t;
2) for 寻转在cache_sizes数组中找到第一个 csizep->cs_size大于size的kmem_cache_t类型的指针。
3) 然后通过 kmem_cache_alloc 分配。

void kmem_cache_reap(int gfp_mask)
    {
        searchp = clock_searchp;
        do {
                unsigned int pages;
                struct list_head* p;
                unsigned int full_free;
                if (searchp->flags & SLAB_NO_REAP)
                        goto next;
                spin_lock_irq(&searchp->spinlock);
                if (searchp->growing)
                        goto next_unlock;
                if (searchp->dflags & DFLGS_GROWN) {
                        searchp->dflags &= ~DFLGS_GROWN;
                        goto next_unlock;
                }
                full_free = 0;
                p = searchp->slabs.prev;
                while (p != &searchp->slabs) {
                        slabp = list_entry(p, slab_t, list);
                        if (slabp->inuse)
                                break;
                        full_free++;
                        p = p->prev;
                }
                pages = full_free * (1<<searchp->gfporder);
                if (searchp->ctor)
                        pages = (pages*4+1)/5;
                if (searchp->gfporder)
                        pages = (pages*4+1)/5;
                if (pages > best_pages) {
                        best_cachep = searchp;
                        best_len = full_free;
                        best_pages = pages;
                        if (full_free >= REAP_PERFECT) {
                                clock_searchp = list_entry(searchp->next.next,
                                                        kmem_cache_t,next);
                                goto perfect;
                        }
                }
                searchp = list_entry(searchp->next.next,kmem_cache_t,next);
        } while (--scan && searchp != clock_searchp);
        clock_searchp = searchp;
        if (!best_cachep)
                goto out;
        spin_lock_irq(&best_cachep->spinlock);
    perfect:
        best_len = (best_len*4 + 1)/5;
        for (scan = 0; scan < best_len; scan++) {
                struct list_head *p;
                if (best_cachep->growing)
                        break;
                p = best_cachep->slabs.prev;
                if (p == &best_cachep->slabs)
                        break;
                slabp = list_entry(p,slab_t,list);
                if (slabp->inuse)
                        break;
                list_del(&slabp->list);
                if (best_cachep->firstnotfull == &slabp->list)
                        best_cachep->firstnotfull = &best_cachep->slabs;
                STATS_INC_REAPED(best_cachep);
                spin_unlock_irq(&best_cachep->spinlock);
                kmem_slab_destroy(best_cachep, slabp);
                spin_lock_irq(&best_cachep->spinlock);
        }
        spin_unlock_irq(&best_cachep->spinlock);
    out:
        up(&cache_chain_sem);
        return;
    }

1) searchp = clock_searchp;
   并不是每次扫描所有的slab队列。clock_searchp 会记住上一次扫描的位置。
2) kmem_slab_destroy(best_cachep, slabp);