/*
*下面的alloc_pages(gfp_mask,order)函数用来请求2^order个连续的页框
*/172
#define alloc_pages(gfp_mask, order) \
173 alloc_pages_node(numa_node_id(), gfp_mask, order)
618 #define numa_node_id() (cpu_to_node(raw_smp_processor_id()))
47 /* Returns the number of the node containing CPU 'cpu' */
48 static inline int cpu_to_node(int cpu)
49 {
50 return cpu_2_node[cpu];
51 }
465 int cpu_2_node[NR_CPUS] __read_mostly = { [0 ... NR_CPUS-1] = 0};//每个CPU都有相互对应的节点，__read_mostly是gcc的一个
//属性
//分配页面函数，这个函数比较复杂，所牵涉到的内容也比较多，尤其是进程方面的内容
144 static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
145 unsigned int order)
146 {
147 if (unlikely(order >= MAX_ORDER)) /*如果要求分配的页数大于MAX_ORDER就以失败告终，这里的MAX_ORDER指的是最大页面号，这里要注意的是对于伙伴算法，所分配的 页面的最大值为2^10，即1024个页面，这一点在伙伴算法中经常会使用到，所以这里的MAX_ORDER的值为11，也就是说如果order的值大于了10，即超出了最大值，那么就会以失败告终，直接以失败返回。*/
148 return NULL; /*从这个判断可以了解到，所分配页的最大的值为 2^10次方，即1KB个页面，即最大不能超过4MB。*/
149
150 /* Unknown node is current node */
151 if (nid < 0)
152 nid = numa_node_id();/*具体实现： #define numa_node_id() (cpu_to_node(raw_smp_processor_id()))
//最后得到的值为0，因为假设现在只有一个CPU */
/*
47 /* Returns the number of the node containing CPU 'cpu'
48 static inline int cpu_to_node(int cpu)
49 {
50 return cpu_2_node[cpu];//int cpu_2_node[NR_CPUS] __read_mostly = { [0 ... NR_CPUS-1] = 0 };/* 这又是C语言中使用的一个新的数组初始化的方法。 //read_mostly是在最后执行的时候被组织到一起，这被认为是为了提高效率，因为在多CPU系统中它改善了访问的时间。*/
51 }
*/
153
154 return __alloc_pages(gfp_mask, order,
155 NODE_DATA(nid)->node_zonelists + gfp_zone(gfp_mask)); /*这是伙伴算法的核心实现，node_zonelists是zone_list类型，gfp_zone的返回值为ZONE_DMA或者是ZONE_NORMAL或ZONE_HIGH，这三个区分别对应着一个值，ZONE_DMA为0，ZONE_NORMAL为1，ZONE_HIGH为2，即__alloc_pages分配页面的管理区由的三个参数决定，如果gfp_zone的返回值为0，就是在ZONE_DMA管理区中分配，如果gfp_zone返回值为1，就是在ZONE_NORMAL中进行分配，如果gfp_zone的返回值为2，就是在ZONE_HIGH中进行分配。*/
//下面是NDOE_DATA的具体定义：
/*
struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;这里的MAX_NUMNODES的值为1，即就定义一个节点
*/
156 }
1232 /*
1233 * This is the 'heart' of the zoned buddy allocator.
* 这个算法是伙伴算法的核心操作
1234 */
1235 struct page * fastcall __alloc_pages(gfp_t gfp_mask, unsigned int order,
1237 struct zonelist *zonelist)
1238 {
1239 const gfp_t wait = gfp_mask & __GFP_WAIT; /*为了实现查看是否允许内核对等待空闲页框的当前进程进行阻塞*/
1240 struct zone **z; //这里为何要使用双重指针？？？
1241 struct page *page; //指向页描述符的指针
1242 struct reclaim_state reclaim_state; //可回收页面操作
81 /*
82 * current->reclaim_state points to one of these when a task is running
83 * memory reclaim
用于回收页面
84 */
1243 struct task_struct *p = current; //将p设置成指向当前进程
1244 int do_retry; //
1245 int alloc_flags; //分配标志
1246 int did_some_progress;
1247
1248 might_sleep_if(wait); //对可能睡眠的函数进行注释
1249
1250 if (should_fail_alloc_page(gfp_mask, order)) /*检查内存分配是否可行，如果不可行就直接返回，即以失败告终，否则就继续执行内存分配*/
1251 return NULL;
1252
1253 restart:
1254 z = zonelist->zones; /* the list of zones suitable for gfp_mask *///首先让z指向第一个管理区
1255
1256 if (unlikely(*z == NULL)) { /*unlikely()宏的功能很有意思的，可以自己去进行验证。这里要实现的如果*z==NULL,那么就返回NULL，否则就继续执行。*/
1257 /* Should this ever happen?? */
1258 return NULL;
1259 }
1261 page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
1262 zonelist, ALLOC_WMARK_LOW|ALLOC_CPUSET); //从空闲链表中获取2^order页内存
//这是get_page_from_freelist函数的原型
// get_page_from_freelist(gfp_t gfp_mask, unsigned int order,struct zonelist *zonelist, int alloc_flags)
1263 if (page)
1264 goto got_pg; //如果获得了相应的页就退出,否则继续执行
1265
1266 /*
1267 * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and
84 #define GFP_THISNODE (__GFP_THISNODE | __GFP_NOWARN | __GFP_NORETRY)
1268 * __GFP_NOWARN set) should not cause reclaim since the subsystem
1269 * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim
1270 * using a larger set of nodes after it has established that the
1271 * allowed per node queues are empty and that nodes are
1272 * over allocated.
1273 */
1274 if (NUMA_BUILD && (gfp_mask & GFP_THISNODE) == GFP_THISNODE) //在不支持NUMA的情况下跳转到nopage处
1275 goto nopage;
1276
1277 for (z = zonelist->zones; *z; z++)
1278 wakeup_kswapd(*z, order);//回收页面操作，待解
/*
1510 *
1511 * A zone is low on free memory, so wake its kswapd task to service it.
1512 *
1513 void wakeup_kswapd(struct zone *zone, int order)
1514 {
1515 pg_data_t *pgdat;
1516
1517 if (!populated_zone(zone)) /*return !!(zone->present_pages) zone->present_pages是以页为单位的管理区的总大小，如果以页为单位的管理区的总大小为0，那么就直接结束退出*/
1518 return;
1519
1520 pgdat = zone->zone_pgdat;
1521 if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1522 return;
1523 if (pgdat->kswapd_max_order < order)
1524 pgdat->kswapd_max_order = order;
1525 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1526 return;
1527 if (!waitqueue_active(&pgdat->kswapd_wait))
1528 return;
1529 wake_up_interruptible(&pgdat->kswapd_wait);
1530 }
*/
1279
1280 /*
1281 * OK, we're below the kswapd watermark and have kicked background
1282 * reclaim. Now things get more complex, so set up alloc_flags according
1283 * to how we want to proceed.
1284 *
1285 * The caller may dip into page reserves a bit more if the caller
1286 * cannot run direct reclaim, or if the caller has realtime scheduling
1287 * policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will
1288 * set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH).
1289 */
1290 alloc_flags = ALLOC_WMARK_MIN; //
/*
890 #define ALLOC_NO_WATERMARKS 0x01 /* don't check watermarks at all *
891 #define ALLOC_WMARK_MIN 0x02 /* use pages_min watermark *
892 #define ALLOC_WMARK_LOW 0x04 /* use pages_low watermark *
893 #define ALLOC_WMARK_HIGH 0x08 /* use pages_high watermark *
894 #define ALLOC_HARDER 0x10 /* try to alloc harder *
895 #define ALLOC_HIGH 0x20 /* __GFP_HIGH set *
896 #define ALLOC_CPUSET 0x40 /* check for correct cpuset *
*/
1291 if ((unlikely(rt_task(p)) && !in_interrupt()) || !wait)
1292 alloc_flags |= ALLOC_HARDER;
1293 if (gfp_mask & __GFP_HIGH)
1294 alloc_flags |= ALLOC_HIGH;
1295 if (wait)
1296 alloc_flags |= ALLOC_CPUSET;
1297
1298 /*
1299 * Go through the zonelist again. Let __GFP_HIGH and allocations
1300 * coming from realtime tasks go deeper into reserves.
1301 *
1302 * This is the last chance, in general, before the goto nopage.
1303 * Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc.
1304 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
1305 */
1306 page = get_page_from_freelist(gfp_mask, order, zonelist, alloc_flags);//在进行了页面回收后再次进行页面的分配操作
1307 if (page)
1308 goto got_pg; //如果分配成功，就成功返回
1309
1310 /* This allocation should allow future memory freeing. */
1311
1312 rebalance:
1313 if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE)))//#define PF_MEMALLOC 0x00000800 /* Allocating memory */ TIF_MEMDIE=16
/*
63 #define test_thread_flag(flag) \
64 test_ti_thread_flag(current_thread_info(), flag)
50 static inline int test_ti_thread_flag(struct thread_info *ti, int flag)
51 {
52 return test_bit(flag,&ti->flags);
53 }
*/
1314 && !in_interrupt()) {
1315 if (!(gfp_mask & __GFP_NOMEMALLOC)) {
1316 nofail_alloc:
1317 /* go through the zonelist yet again, ignoring mins */
1318 page = get_page_from_freelist(gfp_mask, order,
1319 zonelist, ALLOC_NO_WATERMARKS);
1320 if (page)
1321 goto got_pg;
1322 if (gfp_mask & __GFP_NOFAIL) {
1323 congestion_wait(WRITE, HZ/50);
1324 goto nofail_alloc;
1325 }
1326 }
1327 goto nopage;
1328 }
1329
1330 /* Atomic allocations - we can't balance anything */
1331 if (!wait) //原子分配，就跳转到nopage，即没有空闲页
1332 goto nopage;
1333
1334 cond_resched();
1335
1336 /* We now go into synchronous reclaim 现在进入异步回收*/
1337 cpuset_memory_pressure_bump();
1338 p->flags |= PF_MEMALLOC;
1339 reclaim_state.reclaimed_slab = 0;
1340 p->reclaim_state = &reclaim_state;
1341
1342 did_some_progress = try_to_free_pages(zonelist->zones, order, gfp_mask);
1343
1344 p->reclaim_state = NULL;
1345 p->flags &= ~PF_MEMALLOC;
1346
1347 cond_resched();
1348
1349 if (likely(did_some_progress)) {
1350 page = get_page_from_freelist(gfp_mask, order,
1351 zonelist, alloc_flags);
1352 if (page)
1353 goto got_pg;
1354 } else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {//If set the mark of the __GFP_FS zero,Then it doesn't allow the kernel execute the operation depending the filesystem .The mark of __Gfp_NORETRY means that you can allocate the page only once.Here allows allocate many times
1355 /*
1356 * Go through the zonelist yet one more time, keep
1357 * very high watermark here, this is only to catch
1358 * a parallel oom killing, we must fail if we're still
1359 * under heavy pressure.
1360 */
1361 page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
1362 zonelist, ALLOC_WMARK_HIGH|ALLOC_CPUSET);
1363 if (page)
1364 goto got_pg;
1365
1366 /* The OOM killer will not help higher order allocs so fail */
1367 if (order > PAGE_ALLOC_COSTLY_ORDER)
1368 goto nopage;
1369 /*
27 *PAGE_ALLOC_COSTLY_ORDER是那些分配行为被认为是一项花费较大的服务所对应的定值，
28 * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed
29 * costly to service. That is between allocation orders which should
30 * coelesce naturally under reasonable reclaim pressure and those which
31 * will not.
32 *
33 #define PAGE_ALLOC_COSTLY_ORDER 3
*/
1370 out_of_memory(zonelist, gfp_mask, order);
1371 goto restart;
1372 }
1373
1374 /*
1375 * Don't let big-order allocations loop unless the caller explicitly
1376 * requests that. Wait for some write requests to complete then retry.
1377 *
1378 * In this implementation, __GFP_REPEAT means __GFP_NOFAIL for order
1379 * <= 3, but that may not be true in other implementations.
1380 */
1381 do_retry = 0;
1382 if (!(gfp_mask & __GFP_NORETRY)) {
1383 if ((order <= PAGE_ALLOC_COSTLY_ORDER) ||
1384 (gfp_mask & __GFP_REPEAT))
1385 do_retry = 1;
1386 if (gfp_mask & __GFP_NOFAIL)
1387 do_retry = 1;
1388 }
1389 if (do_retry) {
1390 congestion_wait(WRITE, HZ/50);
1391 goto rebalance;
1392 }
1393
1394 nopage:
1395 if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit()) {
1396 printk(KERN_WARNING "%s: page allocation failure."
1397 " order:%d, mode:0x%x\n",
1398 p->comm, order, gfp_mask);
1399 dump_stack();
/*
278 *
279 * The architecture-independent dump_stack generator
280 *
281 void dump_stack(void)
282 {
283 unsigned long stack;
285 show_trace(current, NULL, &stack);
286 }
241 void show_trace(struct task_struct *task, struct pt_regs *regs,
242 unsigned long * stack)
243 {
244 show_trace_log_lvl(task, regs, stack, "");
245 }
*/
1400 show_mem();//如果没有空闲的页就显示内存具体分布，即罗列出相应的信息
1401 }
1402 got_pg:
1403 return page;
1404 }
1405
1406 EXPORT_SYMBOL(__alloc_pages);
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