linux内存管理--实际分配函数 buffered_rmqueue

不管是快速分配还是慢速分配，实际分配内存的都是 buffered_rmqueue()函数，其他的都是在选择从哪个地方来分配比较合适；

还是先来说说各个参数：

struct zone *preferred_zone 表示分配所能接受的最大zone类型

struct zone *zone  表示就在该zone上分配内存；

int  order  表示分配页的阶数

gfp_t gfp_flags  分配的标识

page = buffered_rmqueue(preferred_zone, zone, order,
                        gfp_mask, migratetype);



/*
 * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
 * we cheat by calling it from here, in the order > 0 path.  Saves a branch
 * or two.
 */
static inline
struct page *buffered_rmqueue(struct zone *preferred_zone,
            struct zone *zone, int order, gfp_t gfp_flags,
            int migratetype)
{
    unsigned long flags;
    struct page *page;
    int cold = !!(gfp_flags & __GFP_COLD);//是否指定冷热页

again:
    if (likely(order == 0)) {//分配单页
        struct per_cpu_pages *pcp;
        struct list_head *list;

        local_irq_save(flags);//禁止本地CPU中断，禁止前先保存中断状态
        pcp = &this_cpu_ptr(zone->pageset)->pcp;//获取到cpu高速缓存页
        list = &pcp->lists[migratetype];//根据迁移类型，得到高速缓存区的freelist
        if (list_empty(list)) {//空的，高速缓存没有数据；这可能是上次获取的cpu高速缓存迁移类型和这次不一样
            pcp->count += rmqueue_bulk(zone, 0,
                    pcp->batch, list,
                    migratetype, cold);//该函数向高速缓存中添加内存页，具体分析见文章后面
            if (unlikely(list_empty(list)))
                goto failed;
        }

        if (cold)
            page = list_entry(list->prev, struct page, lru);
        else
            page = list_entry(list->next, struct page, lru);

        list_del(&page->lru);
        pcp->count--;
    } else {
        if (unlikely(gfp_flags & __GFP_NOFAIL)) {
            /*
             * __GFP_NOFAIL is not to be used in new code.
             *
             * All __GFP_NOFAIL callers should be fixed so that they
             * properly detect and handle allocation failures.
             *
             * We most definitely don't want callers attempting to
             * allocate greater than order-1 page units with
             * __GFP_NOFAIL.
             */
            WARN_ON_ONCE(order > 1);
        }
        spin_lock_irqsave(&zone->lock, flags);
        page = __rmqueue(zone, order, migratetype);
        spin_unlock(&zone->lock);
        if (!page)
            goto failed;
        __mod_zone_freepage_state(zone, -(1 << order),
                      get_pageblock_migratetype(page));
    }

    __count_zone_vm_events(PGALLOC, zone, 1 << order);
    zone_statistics(preferred_zone, zone, gfp_flags);
    local_irq_restore(flags);

    VM_BUG_ON(bad_range(zone, page));
    if (prep_new_page(page, order, gfp_flags))
        goto again;
    return page;

failed:
    local_irq_restore(flags);
    return NULL;
}

struct zone结构体中有个  struct per_cpu_pageset __percpu *pageset; 成员，该成员用于冷热分配器，热页表示已经在cpu的高速缓存中了；

struct per_cpu_pageset {
    struct per_cpu_pages pcp;
#ifdef CONFIG_NUMA
    s8 expire;
#endif
#ifdef CONFIG_SMP
    s8 stat_threshold;
    s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];
#endif
};

cpu缓存页数组

struct per_cpu_pages {
    int count;      /* number of pages in the list */列表中页数
    int high;       /* high watermark, emptying needed */列表页数的上限
    int batch;      /* chunk size for buddy add/remove */添加和删除页时，一次操作多少页。不是单页删除和填充的，而是以该单位页来操作的

    /* Lists of pages, one per migrate type stored on the pcp-lists */
    struct list_head lists[MIGRATE_PCPTYPES];//迁移类型的链表
};