Chinaunix首页 | 论坛 | 博客
  • 博客访问: 1030598
  • 博文数量: 123
  • 博客积分: 5051
  • 博客等级: 大校
  • 技术积分: 1356
  • 用 户 组: 普通用户
  • 注册时间: 2008-07-14 10:56
文章分类
文章存档

2012年(1)

2011年(21)

2010年(13)

2009年(55)

2008年(33)

分类: LINUX

2009-06-11 14:58:29

/*
 *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);

阅读(8216) | 评论(0) | 转发(0) |
给主人留下些什么吧!~~