前面分析了memblock算法、内核页表的建立、内存管理框架的构建，这些都是x86处理的setup_arch()函数里面初始化的，因地制宜，具有明显处理器的特征。而start_kernel()接下来的初始化则是linux通用的内存管理算法框架了。
build_all_zonelists()用来初始化内存分配器使用的存储节点中的管理区链表，是为内存管理算法（伙伴管理算法）做准备工作的。具体实现：
【file：/mm/page_alloc.c】
/*
* Called with zonelists_mutex held always
* unless system_state == SYSTEM_BOOTING.
*/
void __ref build_all_zonelists(pg_data_t *pgdat, struct zone *zone)
{
set_zonelist_order();
if (system_state == SYSTEM_BOOTING) {
__build_all_zonelists(NULL);
mminit_verify_zonelist();
cpuset_init_current_mems_allowed();
} else {
#ifdef CONFIG_MEMORY_HOTPLUG
if (zone)
setup_zone_pageset(zone);
#endif
/* we have to stop all cpus to guarantee there is no user
of zonelist */
stop_machine(__build_all_zonelists, pgdat, NULL);
/* cpuset refresh routine should be here */
}
vm_total_pages = nr_free_pagecache_pages();
/*
* Disable grouping by mobility if the number of pages in the
* system is too low to allow the mechanism to work. It would be
* more accurate, but expensive to check per-zone. This check is
* made on memory-hotadd so a system can start with mobility
* disabled and enable it later
*/
if (vm_total_pages < (pageblock_nr_pages * MIGRATE_TYPES))
page_group_by_mobility_disabled = 1;
else
page_group_by_mobility_disabled = 0;
printk("Built %i zonelists in %s order, mobility grouping %s. "
"Total pages: %ld\n",
nr_online_nodes,
zonelist_order_name[current_zonelist_order],
page_group_by_mobility_disabled ? "off" : "on",
vm_total_pages);
#ifdef CONFIG_NUMA
printk("Policy zone: %s\n", zone_names[policy_zone]);
#endif
}首先看到set_zonelist_order()：
【file：/mm/page_alloc.c】
static void set_zonelist_order(void)
{
current_zonelist_order = ZONELIST_ORDER_ZONE;
}此处用于设置zonelist的顺序，ZONELIST_ORDER_ZONE用于表示顺序(-zonetype, [node] distance)，另外还有ZONELIST_ORDER_NODE表示顺序([node] distance, -zonetype)。但其仅限于对NUMA环境存在区别，非NUMA环境则毫无差异。
如果系统状态system_state为SYSTEM_BOOTING，系统状态只有在start_kernel执行到最后一个函数rest_init后，才会进入SYSTEM_RUNNING，于是初始化时将会接着是__build_all_zonelists()函数:
【file：/mm/page_alloc.c】
/* return values int ....just for stop_machine() */
static int __build_all_zonelists(void *data)
{
int nid;
int cpu;
pg_data_t *self = data;
#ifdef CONFIG_NUMA
memset(node_load, 0, sizeof(node_load));
#endif
if (self && !node_online(self->node_id)) {
build_zonelists(self);
build_zonelist_cache(self);
}
for_each_online_node(nid) {
pg_data_t *pgdat = NODE_DATA(nid);
build_zonelists(pgdat);
build_zonelist_cache(pgdat);
}
/*
* Initialize the boot_pagesets that are going to be used
* for bootstrapping processors. The real pagesets for
* each zone will be allocated later when the per cpu
* allocator is available.
*
* boot_pagesets are used also for bootstrapping offline
* cpus if the system is already booted because the pagesets
* are needed to initialize allocators on a specific cpu too.
* F.e. the percpu allocator needs the page allocator which
* needs the percpu allocator in order to allocate its pagesets
* (a chicken-egg dilemma).
*/
for_each_possible_cpu(cpu) {
setup_pageset(&per_cpu(boot_pageset, cpu), 0);
#ifdef CONFIG_HAVE_MEMORYLESS_NODES
/*
* We now know the "local memory node" for each node--
* i.e., the node of the first zone in the generic zonelist.
* Set up numa_mem percpu variable for on-line cpus. During
* boot, only the boot cpu should be on-line; we'll init the
* secondary cpus' numa_mem as they come on-line. During
* node/memory hotplug, we'll fixup all on-line cpus.
*/
if (cpu_online(cpu))
set_cpu_numa_mem(cpu, local_memory_node(cpu_to_node(cpu)));
#endif
}
return 0;
}其中build_zonelists_node()函数实现：
【file：/mm/page_alloc.c】
/*
* Builds allocation fallback zone lists.
*
* Add all populated zones of a node to the zonelist.
*/
static int build_zonelists_node(pg_data_t *pgdat, struct zonelist *zonelist,
int nr_zones)
{
struct zone *zone;
enum zone_type zone_type = MAX_NR_ZONES;
do {
zone_type--;
zone = pgdat->node_zones + zone_type;
if (populated_zone(zone)) {
zoneref_set_zone(zone,
&zonelist->_zonerefs[nr_zones++]);
check_highest_zone(zone_type);
}
} while (zone_type);
return nr_zones;
}populated_zone()用于判断管理区zone的present_pages成员是否为0，如果不为0的话，表示该管理区存在页面，那么则通过zoneref_set_zone()将其设置到zonelist的_zonerefs里面，而check_highest_zone()在没有开启NUMA的情况下是个空函数。由此可以看出build_zonelists_node()实则上是按照ZONE_HIGHMEM—>ZONE_NORMAL—>ZONE_DMA的顺序去迭代排布到_zonerefs里面的，表示一个申请内存的代价由低廉到昂贵的顺序，这是一个分配内存时的备用次序。
回到build_zonelists()函数中，而它代码显示将本地的内存管理区进行分配备用次序排序，接着再是分配内存代价低于本地的，最后才是分配内存代价高于本地的。
分析完build_zonelists()，再回到__build_all_zonelists()看一下build_zonelist_cache()：
【file：/mm/page_alloc.c】
/* non-NUMA variant of zonelist performance cache - just NULL zlcache_ptr */
static void build_zonelist_cache(pg_data_t *pgdat)
{
pgdat->node_zonelists[0].zlcache_ptr = NULL;
}该函数与CONFIG_NUMA相关，用来设置zlcache相关的成员。由于没有开启该配置，故直接设置为NULL。
基于build_all_zonelists()调用__build_all_zonelists()入参为NULL，由此可知__build_all_zonelists()运行的代码是：
for_each_online_node(nid) {
pg_data_t *pgdat = NODE_DATA(nid);
build_zonelists(pgdat);
build_zonelist_cache(pgdat);
}主要是设置各个内存管理节点node里面各自的内存管理分区zone的内存分配次序。
__build_all_zonelists()接着的是：
for_each_possible_cpu(cpu) {
setup_pageset(&per_cpu(boot_pageset, cpu), 0);
#ifdef CONFIG_HAVE_MEMORYLESS_NODES
if (cpu_online(cpu))
set_cpu_numa_mem(cpu, local_memory_node(cpu_to_node(cpu)));
#endif
}其中CONFIG_HAVE_MEMORYLESS_NODES未配置，主要分析一下setup_pageset()：
【file：/mm/page_alloc.c】
static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
{
pageset_init(p);
pageset_set_batch(p, batch);
}setup_pageset()里面调用的两个函数较为简单，就直接过一下。先是：
【file：/mm/page_alloc.c】
static void pageset_init(struct per_cpu_pageset *p)
{
struct per_cpu_pages *pcp;
int migratetype;
memset(p, 0, sizeof(*p));
pcp = &p->pcp;
pcp->count = 0;
for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++)
INIT_LIST_HEAD(&pcp->lists[migratetype]);
}pageset_init()主要是将struct per_cpu_pages结构体进行初始化，而pageset_set_batch()则是对其进行设置。pageset_set_batch()实现：
【file：/mm/page_alloc.c】
/*
* pcp->high and pcp->batch values are related and dependent on one another:
* ->batch must never be higher then ->high.
* The following function updates them in a safe manner without read side
* locking.
*
* Any new users of pcp->batch and pcp->high should ensure they can cope with
* those fields changing asynchronously (acording the the above rule).
*
* mutex_is_locked(&pcp_batch_high_lock) required when calling this function
* outside of boot time (or some other assurance that no concurrent updaters
* exist).
*/
static void pageset_update(struct per_cpu_pages *pcp, unsigned long high,
unsigned long batch)
{
/* start with a fail safe value for batch */
pcp->batch = 1;
smp_wmb();
/* Update high, then batch, in order */
pcp->high = high;
smp_wmb();
pcp->batch = batch;
}
/* a companion to pageset_set_high() */
static void pageset_set_batch(struct per_cpu_pageset *p, unsigned long batch)
{
pageset_update(&p->pcp, 6 * batch, max(1UL, 1 * batch));
}setup_pageset()函数入参p是一个struct per_cpu_pageset结构体的指针，per_cpu_pageset结构是内核的各个zone用于每CPU的页面高速缓存管理结构。该高速缓存包含一些预先分配的页面，以用于满足本地CPU发出的单一内存请求。而struct per_cpu_pages定义的pcp是该管理结构的成员，用于具体页面管理。原本是每个管理结构有两个pcp数组成员，里面的两条队列分别用于冷页面和热页面管理，而当前分析的3.14.12版本已经将两者合并起来，统一管理冷热页，热页面在队列前面，而冷页面则在队列后面。暂且先记着这么多，后续在Buddy算法的时候再详细分析了。
**至此，可以知道__build_all_zonelists()是内存管理框架向后续的内存页面管理算法做准备，排布了内存管理区zone的分配次序，同时初始化了冷热页管理。**
最后回到build_all_zonelists()函数。由于没有开启内存初始化调试功能CONFIG_DEBUG_MEMORY_INIT，mminit_verify_zonelist()是一个空函数。
基于CONFIG_CPUSETS配置项开启的情况下，而cpuset_init_current_mems_allowed()实现如下：
【file：/kernel/cpuset.c】
void cpuset_init_current_mems_allowed(void)
{
nodes_setall(current->mems_allowed);
}这里面的current 是一个cpuset的数据结构，用来管理cgroup中的任务能够使用的cpu和内存节点。而成员mems_allowed，该成员是nodemask_t类型的结构体
【file：/include/linux/nodemask.h】
typedef struct { DECLARE_BITMAP(bits, MAX_NUMNODES); } nodemask_t;该结构其实就是定义了一个位域，每个位对应一个内存结点，如果置1表示该节点内存可用。而nodes_setall则是将这个位域中每个位都置1。
末了看一下build_all_zonelists()里面nr_free_pagecache_pages()的实现：
【file：/mm/page_alloc.c】
/**
* nr_free_pagecache_pages - count number of pages beyond high watermark
*
* nr_free_pagecache_pages() counts the number of pages which are beyond the
* high watermark within all zones.
*/
unsigned long nr_free_pagecache_pages(void)
{
return nr_free_zone_pages(gfp_zone(GFP_HIGHUSER_MOVABLE));
}而里面调用的nr_free_zone_pages()实现为：
【file：/mm/page_alloc.c】
/**
* nr_free_zone_pages - count number of pages beyond high watermark
* @offset: The zone index of the highest zone
*
* nr_free_zone_pages() counts the number of counts pages which are beyond the
* high watermark within all zones at or below a given zone index. For each
* zone, the number of pages is calculated as:
* managed_pages - high_pages
*/
static unsigned long nr_free_zone_pages(int offset)
{
struct zoneref *z;
struct zone *zone;
/* Just pick one node, since fallback list is circular */
unsigned long sum = 0;
struct zonelist *zonelist = node_zonelist(numa_node_id(), GFP_KERNEL);
for_each_zone_zonelist(zone, z, zonelist, offset) {
unsigned long size = zone->managed_pages;
unsigned long high = high_wmark_pages(zone);
if (size > high)
sum += size - high;
}
return sum;
}可以看到nr_free_zone_pages()遍历所有内存管理区并将各管理区的内存空间求和，其实质是用于统计所有的管理区可以用于分配的内存页面数。
接着在build_all_zonelists()后面则是判断当前系统中的内存页框数目，以决定是否启用流动分组机制(Mobility Grouping)，该机制可以在分配大内存块时减少内存碎片。通常只有内存足够大时才会启用该功能，否则将会提升消耗降低性能。其中pageblock_nr_pages表示伙伴系统中的最高阶页块所能包含的页面数。
至此，内存管理框架算法基本准备完毕。